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AAA COLLEGE OF ENGINEERING & TECHNOLOGY
Accredited by NBA (CSE, ECE, EEE & MECHANICAL), (Accredited by NAAC with “A” grade)
(Approved by AICTE, New Delhi & Affiliated to Anna University, Chennai)
(An ISO 21001: 2018 Certified Institution)
Amathur, Sivakasi - 626 005.
Department of Mechanical Engineering
CME397 Surface Engineering
(Professional Elective)
Name of the Student :
Register Number :
Class / Semester : III YEAR / VI SEMESTER
Academic Year : 2023– 2024
Regulation : 2021
Name of the Course Instructor : M.Karthikeyan AP/MECH
Syllabus
UNIT – I SURFACES AND FRICTION
Basics of surfaces features – Roughness parameters – surface measurement -
Cause of friction- Laws of friction – Static friction – Rolling Friction – Stick-slip
Phenomenon - Friction properties of metal and nonmetals – Friction in extreme
conditions – Thermal considerations in sliding contact.
UNIT – II WEAR
Laws of Wear - Types of Wear mechanism – wear debris analysis - Theoretical
wear models - Wear of metals and nonmetals – International standards in friction
and wear measurements
UNIT – III CORROSION
Introduction – Types of corrosion – Factors influencing corrosion – Testing of
corrosion – In-service monitoring, Simulated service, Laboratory testing –
Prevention of Corrosion – Material selection, Alteration of environment, Design,
Cathodic and Anodic Protection, Corrosion inhibitors
UNIT – IV SURFACE TREATMENTS
Surface properties – Hydrophobic – Super hydrophobic – Hydrophilic - surface
metallurgy –Surface coating Techniques – PVD – CVD – Physical CVD – Ion
implantation – Surface welding – Thermal spraying – Laser surface hardening and
alloying - New trends in coating technology – DLC – CNC – Thick coatings –
Nanoengineered coatings – Other coatings, Corrosion resistant coatings
UNIT – V ENGINEERING MATERIALS
Introduction – High and low friction materials - Advanced alloys – Super alloys,
Titanium alloys, Magnesium alloys, Aluminium alloys, and Nickel based alloys –
Ceramics – Polymers – Biomaterials – Bio Tribology -Nano Tribology
TOTAL:45 PERIODS
UNIT – I SURFACES AND FRICTION
Basics of surfaces features – Roughness parameters – surface measurement -
Cause of friction- Laws of friction – Static friction – Rolling Friction – Stick-slip
Phenomenon - Friction properties of metal and nonmetals – Friction in extreme
conditions – Thermal considerations in sliding contact.
Basics of surfaces features
 Surface features refer to the characteristics, irregularities, and patterns
present on the outermost layer of a material or object.
 Understanding and characterizing surface features are essential for optimizing
material performance, enhancing product functionality, improving
manufacturing processes, and ensuring quality control in various industries
and applications.
 Techniques such as scanning electron microscopy (SEM), atomic force
microscopy (AFM), profilometry, and optical microscopy are commonly used
to analyze and quantify surface features at different length scales.
 Some fundamental aspects of surface features are
1. Topography:
 Surface topography refers to the three-dimensional structure or landscape of
a surface, including its height variations, roughness, and texture.
 Topographic features can range from microscale to macroscale, and they play a
crucial role in determining the functional properties of a surface, such as friction,
adhesion, wear resistance, and optical properties.
2. Roughness:
 Surface roughness refers to the irregularities or deviations from an ideal flat
surface on a microscopic scale.
 Roughness can be quantified using parameters such as Ra (Arithmetic Average
Roughness), Rz (Average Maximum Height), Rq (Root Mean Square Roughness),
and others.
 It influences the appearance, feel, and performance of surfaces, impacting factors
such as friction, lubrication, and contact mechanics.
3. Texture:
 Surface texture encompasses the arrangement and distribution of microscale
features on a surface, including patterns, grains, grooves, and ridges.
 Texture affects the visual appearance, tactile feel, and functionality of
surfaces.
 It is often characterized by parameters such as spatial frequency, orientation,
and amplitude of surface features.
4. Waviness:
 Surface waviness refers to the broader, low-frequency undulations or periodic
variations in surface roughness.
 Waviness typically occurs on a larger scale than roughness features and can be
caused by factors such as machining processes, tool vibrations, or material
properties.
 It is important to distinguish waviness from roughness when analyzing surface
profiles.
5. Defects:
 Surface defects are irregularities or imperfections on a surface that deviate
from the desired or intended structure.
 Common surface defects include scratches, pits, cracks, porosity, and
contamination.
 Defects can affect the structural integrity, functionality, and aesthetic quality of
surfaces, making them a crucial consideration in quality control and inspection
processes.
6. Anisotropy:
 Surface anisotropy refers to the directional dependence of surface properties
or features.
 Anisotropic surfaces exhibit different characteristics or behaviors depending on
the direction of measurement or observation.
 Anisotropy can arise from factors such as material processing methods,
crystallographic orientation, or surface treatments.
7. Tribological Properties:
 Surface features play a significant role in determining the tribological properties
of materials, including friction, wear, and lubrication behavior.
 The interaction between surface asperities, roughness, and lubricants influences
the performance and durability of mechanical components, coatings, and
interfaces.
Roughness parameters
1. Traversing Length:
 It is denoted by LT.
 The traversing length refers to the distance over which the stylus travels along
the surface.
2. Assessment Length:
 It is denoted by LM.
 In roughness measurement, the assessment length refers to the segment of the
surface profile over which roughness parameters are calculated and
evaluated.
3. Sampling Length:
 It is the length of a section inside the assessment length.
 It is equivalent to the wavelength of the filter.
 It is denoted by LV.
4. Ra (Arithmetic Average Roughness):
 Ra represents the arithmetic average of the absolute values of the profile
heights over the evaluation length.
 It provides a general indication of the height deviations of the surface.
5. Rz (Average Maximum Height):
 Rz measures the average of the heights of the five highest peaks and the five
deepest valleys in the sampling length.
 It provides information about the extremes of the surface roughness profile.
6. Rp (Maximum Peak Height) and Rv (Maximum Valley Depth):
 Rp and Rv represent the maximum peak height and the maximum valley
depth, respectively, within the evaluation length.
7. Rq (Root Mean Square Roughness):
 Rq is the square root of the arithmetic mean of the squares of the profile
heights within the evaluation length.
 It provides a measure of the root-mean-square deviation of the surface roughness
profile.
8. Rt (Total Roughness):
 Rt represents the difference between the highest peak and the deepest
valley within the evaluation length.
 It provides information about the overall height variation of the surface.
9. Rmax (Maximum Height):
 Rmax is the height of the highest peak within the evaluation length.
 It represents the maximum height deviation of the surface.
10. Rmr (Material Ratio):
 Rmr is the ratio of the material volume above the mean line to the total
evaluation length.
 It characterizes the predominant material ratio of the surface.
11. S (Lay):
 S is a parameter that describes the predominant direction of the surface texture.
 It can be measured as the average spacing between the surface features.
All these parameters are typically determined using profilometers or other
specialized instruments capable of measuring surface profiles. Different
applications may require different parameters depending on the specific surface
characteristics that are of interest.
Surface measurement
 Surface measurement refers to the process of quantitatively assessing various
characteristics of a surface, such as roughness, topography, texture, and
morphology.
 These measurements are crucial for evaluating the quality, functionality, and
performance of surfaces in diverse fields including manufacturing, engineering,
materials science, and biology.
 Surface measurement techniques are selected based on factors such as the
desired resolution, measurement speed, sample properties, and the specific
features of interest.
 Here are some common methods used for surface measurement:
1. Contact Profilometry:
 Contact profilometry involves using a stylus or probe to physically trace the
surface profile.
 As the probe moves across the surface, it records the vertical displacement,
allowing for the calculation of surface roughness parameters such as Ra, Rz, and
Rq.
 Contact profilometers are versatile instruments suitable for a wide range of
surfaces and materials.
2. Non-contact Profilometry:
 Non-contact profilometry methods, such as optical profilometry and confocal
microscopy, use optical principles to measure surface topography without
physically touching the surface.
 These techniques offer high resolution, fast data acquisition, and non-
destructive measurement capabilities, making them suitable for delicate or soft
materials.
3. Atomic Force Microscopy (AFM):
 AFM is a high-resolution imaging technique that uses a sharp tip mounted on a
cantilever to scan the surface in a raster pattern.
 By measuring the deflection of the cantilever as it interacts with the surface, AFM
can generate three-dimensional images with nanometer-scale resolution.
 AFM is particularly useful for studying nanoscale features and surface properties
of materials.
4. Scanning Electron Microscopy (SEM):
 SEM provides detailed images of surface morphology and topography by
scanning the surface with a focused beam of electrons.
 SEM offers high magnification capabilities and can reveal fine surface structures
and features with sub-micron resolution.
 It is widely used for characterizing materials in materials science, geology, and
biology.
5. Optical Microscopy:
 Optical microscopy is a versatile and widely used technique for visualizing
surface features and structures.
 Depending on the configuration and magnification of the microscope, optical
microscopy can provide detailed images of surface morphology, texture, and
defects.
 Advanced techniques such as polarized light microscopy offer enhanced contrast
and visualization capabilities.
6. Surface Roughness Testers:
 Surface roughness testers, also known as surface roughness meters or
profilometers, are portable instruments designed specifically for measuring
surface roughness parameters.
 These devices typically use a skid-mounted stylus or a non-contact sensor to
scan the surface and provide real-time roughness measurements on-site.
7. White Light Interferometry (WLI):
 WLI is an optical technique that utilizes the interference pattern generated by
white light reflected from the surface to measure surface height variations with
sub-nanometer resolution.
 WLI is capable of producing high-resolution, three-dimensional surface maps and
is widely used in metrology and semiconductor industry applications.
Cause of friction
 Friction is the force that opposes the relative motion or tendency of motion
between two surfaces in contact.
 It is caused by various microscopic and macroscopic interactions between the
contacting surfaces.
 Understanding the causes of friction is essential for designing materials,
components, and systems with optimized tribological properties.
 By mitigating frictional losses and wear, engineers can improve the efficiency,
reliability, and longevity of mechanical systems in various applications.
 The primary causes of friction include:
1. Adhesion:
 Adhesion is the phenomenon where molecules from the surfaces in contact
attract each other, leading to the formation of molecular bonds across the
interface.
 These adhesive forces create resistance to sliding or motion between the
surfaces.
 Adhesion is particularly significant in materials with high surface energy or when
the surfaces are in close contact.
2. Surface Roughness:
 Surface roughness refers to the irregularities or asperities present on the
surfaces in contact.
 When two surfaces slide against each other, the asperities interlock, causing
resistance to motion.
 The degree of surface roughness influences the magnitude of friction, with
rougher surfaces typically exhibiting higher friction coefficients.
3. Deformation:
 When two surfaces are pressed together, they deform at the contact points due to
the applied load.
 Deformation increases the real contact area between the surfaces, leading
to higher frictional forces.
 The extent of deformation depends on the mechanical properties of the materials,
such as hardness, elasticity, and plasticity.
4. Surface Properties:
 The chemical composition, surface energy, and surface treatments of
materials influence their frictional behavior.
 For example, materials with higher surface energy tend to exhibit stronger
adhesive forces and higher friction coefficients.
 Additionally, surface treatments such as lubrication or surface coatings can
modify the frictional characteristics of materials.
5. Temperature:
 Frictional forces can generate heat at the interface between two sliding surfaces.
 Increased temperature can affect the properties of the materials and the
nature of surface interactions, leading to changes in friction behavior.
 In some cases, elevated temperatures may reduce friction by promoting
lubrication or by altering material properties.
6. Lubrication:
 Lubrication involves the introduction of a lubricant between two sliding surfaces
to reduce friction and wear.
 Lubricants can act as a barrier between the surfaces, minimizing direct contact
and reducing adhesive forces.
 Different types of lubricants, such as oils, greases, and solid lubricants, are used
depending on the application requirements and operating conditions.
7. Velocity:
 The relative velocity between two surfaces affects the magnitude and nature of
frictional forces.
 The friction may decrease with increasing velocity, particularly in regimes
where fluid lubrication becomes more effective.
Laws of friction
 The laws of friction describe the fundamental principles governing the interaction
between two solid surfaces in contact.
 These laws were first formulated by Leonardo da Vinci and later refined by
Amontons and Coulomb.
 The laws of friction can be summarized as follows:
1. Coulomb's Law of Friction:
 Coulomb's law states that the force of friction between two surfaces is
proportional to the normal force pressing the surfaces together.
 Mathematically, Coulomb's law can be expressed as Ff=μN, where:
 Ff is the force of friction.
 μ is the coefficient of friction, which is a dimensionless constant representing the
frictional characteristics of the surfaces.
 N is the normal force exerted perpendicular to the surfaces.
2. Direction of Friction:
 The force of friction Ff always acts parallel to the surfaces in contact and
opposes the relative motion or tendency of motion between the surfaces.
 The direction of friction is determined by the direction of the applied force or
motion.
3. Static Friction:
 Static friction refers to the resistance to motion experienced by stationary
objects in contact.
 The force of static friction (Ffs) can vary and is generally equal to or less than the
maximum possible static friction force, which is given by Ffs=μsN, where μs is the
coefficient of static friction.
 Static friction prevents the motion of an object until an external force overcomes
it.
4. Kinetic Friction:
 Kinetic friction, also known as sliding friction or dynamic friction, refers to the
resistance to motion experienced by objects in motion relative to each other.
 The force of kinetic friction (Ffk) is generally less than the maximum possible static
friction force and is given by Ffk=μkN, where μk is the coefficient of kinetic friction.
 Kinetic friction opposes the relative motion between surfaces and acts to slow
down moving objects.
5. Dependence on Surface Roughness and Material Properties:
 The coefficients of friction (μ) depend on the nature of the surfaces in contact,
including their roughness, surface texture, and material properties.
 Smooth surfaces typically exhibit lower coefficients of friction compared to
rough surfaces.
 The coefficients of friction can vary depending on factors such as surface
lubrication, temperature, and contact pressure.
These laws of friction provide a foundation for understanding and predicting the
behavior of frictional forces in various mechanical systems, influencing the design,
operation, and maintenance of machinery and structures.
Static friction
Static friction is the resistance force that prevents two stationary objects from
moving relative to each other when an external force is applied.
It acts parallel to the surfaces in contact and opposes the impending motion or
tendency of motion between the objects.
Here are some key points about static friction:
1. Prevents Motion: Static friction arises when there is an external force
acting on an object but the object remains stationary. The force of static
friction precisely balances the applied force, preventing motion.
2. Maximum Limit: The force of static friction can vary and is generally equal
to or less than the maximum possible static friction force. This maximum
static friction force is determined by the coefficient of static friction (μs)
multiplied by the normal force (N) pressing the surfaces together: Ffs=μsN.
3. Dependent on Applied Force: The force of static friction increases
proportionally with the magnitude of the applied force until it reaches its
maximum value. If the applied force exceeds the maximum static friction
force, the object will start moving, and kinetic friction will take over.
4. Dependent on Surface Characteristics: The coefficient of static friction (μs)
depends on the nature of the surfaces in contact, including their roughness,
surface texture, and material properties. Smooth surfaces typically have
lower coefficients of static friction compared to rough surfaces.
5. No Motion, No Wear: Since static friction prevents motion, it does not
result in wear or surface damage between stationary objects. However, it
contributes to the wear when the objects transition from static to kinetic
friction.
6. Applications: Static friction is crucial in various applications, such as
keeping objects in place on surfaces (e.g., preventing a book from sliding off
a table), maintaining traction between tires and roads, and allowing
machinery to start and stop smoothly without slipping.
Understanding static friction is essential in engineering and everyday life, as it
influences the design of structures, machinery, and transportation systems,
ensuring stability, safety, and efficiency.
Rolling Friction
 Rolling friction, also known as rolling resistance, is the resistance force that
occurs when one object rolls over another.
 Unlike sliding friction, which occurs when two surfaces slide past each other,
rolling friction involves the interaction between a rolling object and the surface
over which it rolls.
 Understanding rolling friction is essential in the design and operation of vehicles,
machinery, and other systems where rolling motion is involved. Minimizing rolling
friction can improve efficiency, reduce energy consumption, and enhance
performance.
 Here are some key points about rolling friction:
1. Mechanism:
 Rolling friction arises due to deformation and interaction between the rolling
object and the surface it rolls on.
 As the object rolls, there is a region of contact between the object and the surface,
where deformation and adhesion occur.
2. Direction:
 Rolling friction acts parallel to the surface and opposes the motion of the rolling
object.
 It acts in the direction opposite to the direction of rolling motion.
3. Dependence on Surface Properties:
 Rolling friction depends on various factors, including the roughness, texture, and
material properties of the rolling object and the surface it rolls on.
 Smoother surfaces generally experience lower rolling friction.
4. Dependence on Load:
 Rolling friction is influenced by the weight or load pressing the rolling object
against the surface.
 Heavier objects typically experience higher rolling friction.
5. Reduced Energy Loss:
 Compared to sliding friction, rolling friction results in less energy loss because the
object deforms and rebounds during each rotation, rather than continuously
sliding and dissipating energy as heat.
6. Applications:
 Rolling friction is encountered in various everyday situations, such as when a
vehicle rolls on a road, a ball rolls on the ground, or a wheel rolls on a surface.
 It is also a significant factor in the efficiency of machinery, transportation
systems, and mechanical systems involving rotating components.
7. Coefficient of Rolling Friction:
 Similar to sliding friction, rolling friction can be quantified by a coefficient of
rolling friction (μr), which represents the ratio of the rolling friction force to the
normal force pressing the rolling object against the surface.
Stick-slip Phenomenon
 https://www.tribonet.org/news/general-topics/stick-slip-phenomenon/
In tribology, the stick-slip phenomenon refers to the irregular motion that occurs
when two surfaces slide against each other, alternating between periods of
sticking and slipping.
 This phenomenon is of significant interest in tribology because it directly impacts
friction, wear, and the overall performance of mechanical systems.
 Here's how the stick-slip phenomenon manifests in tribological contexts:
1. Interfacial Friction:
 At the interface between two surfaces, there's a force resisting their relative
motion, known as friction.
 When the applied force exceeds a certain threshold, the surfaces overcome
static friction and begin to move.
 However, due to irregularities in surface topography, the surfaces don't
move smoothly; they momentarily stick together before slipping.
 This sticking and slipping cycle repeats, causing the jerky motion
characteristic of stick-slip behavior.
2. Energy Dissipation:
 During the sticking phase, energy accumulates in the form of elastic
deformation and interfacial adhesion.
 When the applied force exceeds the threshold, this stored energy is
suddenly released during slipping, leading to rapid motion and often
generating vibrations and noise.
 This energy dissipation contributes to wear and can affect the efficiency and
performance of tribological systems.
3. Influence of Lubrication:
 Lubricants play a crucial role in tribology by reducing friction and wear
between sliding surfaces.
 In the context of stick-slip, lubrication can help mitigate the phenomenon
by providing a fluid film that separates the surfaces and reduces the
likelihood of them sticking together.
 Proper lubrication selection and maintenance are essential for minimizing
stick-slip and ensuring smooth operation in mechanical systems.
4. Surface Roughness and Contact Mechanics:
 Surface roughness and the nature of surface interactions significantly
influence stick-slip behavior.
 Rough surfaces tend to have more frequent and pronounced stick-slip
motion compared to smoother surfaces.
 Additionally, the contact mechanics at the interface, including adhesion and
plowing effects, affect the magnitude and duration of stick and slip events.
5. Control and Mitigation:
 Engineers employ various techniques to control and mitigate stick-slip in
tribological systems.
 This may involve surface treatments to reduce roughness and enhance
lubrication effectiveness, optimization of operating conditions (e.g., load,
speed), and the design of damping mechanisms to suppress vibrations
associated with stick-slip motion.
Understanding and effectively managing stick-slip phenomena are crucial for
improving the reliability, durability, and efficiency of mechanical systems across
diverse industrial applications, ranging from automotive components to
manufacturing machinery and precision equipment. Tribologists continuously
research and develop strategies to better understand, predict, and control stick-
slip behavior to address the challenges posed by friction and wear in real-world
applications.
Friction properties of metals
Metals exhibit different friction properties depending on factors like surface
roughness, lubrication, temperature, and load. Here are some key points:
• Static Friction: The friction between stationary surfaces. Metals can have high
static friction due to interlocking irregularities on their surfaces
• Kinetic Friction: The friction between moving surfaces. Metals generally have
lower kinetic friction compared to static friction but can still vary based on
factors like surface finish and lubrication.
• Surface Roughness: Rough surfaces create more friction due to increased
contact points. Polishing or smoothing metal surfaces reduces friction by
minimizing contact points.
• Lubrication: Adding lubricants like oils or greases can significantly reduce friction
between metal surfaces by creating a barrier between them.
• Temperature: Friction between metals typically decreases with increasing
temperature due to reduced intermolecular forces at higher temperatures.
• Load: Heavier loads can increase friction between metal surfaces due to
higher contact pressures, especially in the case of rough surfaces.
• Metal Type: Different metals have varying friction properties. For example, softer
metals like lead or aluminum generally have lower friction coefficients
compared to harder metals like steel.
• Understanding these factors helps engineers optimize friction properties for
specific applications, such as machinery, automotive components, or
manufacturing processes.
Friction properties of nonmetals
• Friction properties of non-metals, such as plastics, ceramics, and polymers, differ
from those of metals due to their distinct material characteristics. Here's an
overview:
• Coefficient of Friction: Non-metals often have lower coefficients of friction
compared to metals, meaning they typically require less force to initiate motion
between surfaces
• Surface Roughness: Similar to metals, surface roughness influences friction in
non-metals. Rough surfaces create more friction, while smoother surfaces reduce
friction.
• Lubrication: Non-metals can benefit from lubrication to further reduce friction.
Lubricants like silicone-based oils or greases are commonly used with non-metal
surfaces to minimize friction and wear.
• Temperature Sensitivity: Some non-metals, like plastics, may experience
changes in friction properties with temperature variations. For example,
certain polymers can become softer and exhibit lower friction at higher
temperatures.
• Wear Resistance: Non-metals generally have lower wear resistance compared
to metals, which can affect their friction properties over time. Surface treatments
or coatings may be applied to enhance wear resistance and maintain consistent
friction levels.
• Chemical Compatibility: Non-metals may exhibit specific friction behaviors in
different chemical environments. For example, exposure to certain chemicals can
alter the surface properties of polymers, affecting their friction characteristics.
• Deformation: Non-metals can deform more easily under load compared to metals.
This deformation can influence friction by changing the contact area and surface
roughness between mating surfaces.
• Understanding these properties is crucial for designing components and systems
where non-metallic materials are used, such as in automotive components,
consumer electronics, biomedical devices, and various industrial applications.
Friction in extreme conditions
Friction in extreme conditions happens when things rub together under intense
pressure, speed, or temperature. This can occur in machinery, engines, or even in
space where conditions are harsh. In extreme situations, friction generates a lot of
heat, which can damage parts or cause them to wear out faster. Engineers tackle
this by using special materials that can handle high temperatures and pressures,
and they often apply lubricants to reduce friction and heat. Additionally, cooling
systems may be installed to prevent overheating. Managing friction in extreme
conditions is crucial to ensure machines and systems operate smoothly and
safely.
Friction and wear under vacuum
Friction and wear under vacuum conditions pose unique challenges compared to
normal atmospheric conditions. In vacuum environments, such as those found in
space or in certain industrial processes, there's typically a lack of air or other
gases that can act as lubricants or provide cooling. This absence of lubrication
and cooling mechanisms can lead to increased friction and wear between surfaces
in contact.
One of the main issues is that without a lubricant, surfaces can stick together
more readily, leading to higher friction forces. This can cause parts to wear out
faster or even seize up altogether.
Furthermore, without air to dissipate heat, the heat generated by friction can't
easily escape, potentially leading to overheating and thermal damage to
components.
To address these challenges, engineers often use specialized materials that have
low friction coefficients and high resistance to wear, even in vacuum
environments. They may also design components with surface coatings or
treatments to reduce friction and wear.
In some cases, alternative lubrication methods, such as solid lubricants or dry
lubricants, may be used that don't rely on the presence of air. These lubricants
can provide a protective layer between surfaces even in the absence of
atmospheric gases.
Overall, managing friction and wear under vacuum conditions requires careful
consideration of materials, lubrication methods, and design strategies to ensure
the reliable operation of components and systems in these challenging
environments.
Friction and wear under low temperatures
Friction and wear under low temperatures can present unique challenges due to
changes in material properties and lubricant behavior. Here are some key points
to consider:
1. Material Properties: At low temperatures, materials may become more brittle and
less ductile. This can lead to increased susceptibility to cracking and fracture
under mechanical stress. Additionally, some materials may experience changes in
their coefficient of friction at low temperatures.
2. Lubricant Viscosity: Many lubricants experience an increase in viscosity as
temperature decreases. This can affect their ability to flow and provide adequate
lubrication between moving parts. In extreme cases, lubricants may solidify or
form gel-like structures, reducing their effectiveness.
3. Boundary Lubrication: Under low temperatures, the formation of an effective
lubricating film between contacting surfaces may be hindered. This can result in
higher levels of boundary lubrication, where direct metal-to-metal contact occurs,
leading to increased friction and wear.
4. Surface Roughness: Cold temperatures can exacerbate the effects of surface
roughness on friction and wear. Microscopic asperities on surfaces may become
more pronounced, increasing the likelihood of abrasive wear and surface damage.
5. Material Compatibility: Some materials may undergo phase changes or
dimensional changes at low temperatures, affecting their compatibility with other
materials in contact. Differential thermal contraction between materials can also
lead to increased stress at their interfaces, promoting wear.
6. Cryogenic Conditions: In extremely low temperatures, such as those
encountered in cryogenic applications, conventional lubricants may not be
suitable. Specialized lubricants designed for use in cryogenic environments are
often required to maintain adequate lubrication and prevent excessive wear.
To mitigate friction and wear under low temperatures, it's essential to select
materials and lubricants that are suitable for the operating conditions. This may
involve using materials with improved low-temperature toughness, selecting
lubricants with low pour points and good flow properties at low temperatures, and
employing surface treatments or coatings to reduce friction and wear.
Additionally, proper equipment design and maintenance practices can help
minimize the effects of low temperatures on friction and wear.
Friction and wear under high temperatures
Friction and wear under high temperatures can also present significant
challenges, often requiring specialized materials, lubricants, and operating
conditions. Here are some key considerations:
1. Thermal Expansion: At high temperatures, materials tend to expand, which can
affect the clearances and tolerances between moving parts. Differential thermal
expansion between mating surfaces can lead to increased contact pressures and
accelerated wear.
2. Softening and Melting: High temperatures can cause materials to soften or even
melt, reducing their strength and increasing their susceptibility to deformation
and surface damage. This can result in increased rates of wear, particularly in
applications involving high contact pressures or sliding velocities.
3. Oxidation and Degradation: Many materials undergo oxidative degradation at
high temperatures, leading to changes in their surface properties and increased
friction and wear. Oxidation can result in the formation of oxides, which may act
as abrasive particles or promote adhesive wear between sliding surfaces.
4. Lubricant Degradation: Lubricants can degrade at high temperatures, losing
their viscosity, thermal stability, and lubricating properties. Oxidation, thermal
breakdown, and evaporation can all contribute to lubricant degradation, leading to
increased friction and wear.
5. Surface Hardening: In some cases, high temperatures can induce surface
hardening of materials through processes such as diffusion, precipitation, or
transformation hardening. While surface hardening can improve wear resistance,
it may also increase friction and promote abrasive wear if not properly controlled.
6. Thermal Runaway: In extreme cases, such as in high-speed or heavy-load
applications, high temperatures can lead to thermal runaway, where frictional
heat generation exceeds the heat dissipation capacity of the system. This can
result in localized melting, welding, or catastrophic failure of components.
To address friction and wear under high temperatures, several strategies can be
employed:
 High-Temperature Materials: Selecting materials with high-temperature stability,
such as heat-resistant alloys or ceramics, can help mitigate wear at elevated
temperatures.
 Specialized Lubricants: Using lubricants specifically formulated for high-
temperature applications, such as synthetic oils or solid lubricants, can help
maintain lubrication effectiveness and reduce friction and wear.
 Surface Treatments: Applying coatings or surface treatments, such as nitriding,
ceramic coatings, or diamond-like carbon (DLC) coatings, can improve surface
hardness and wear resistance at high temperatures.
 Cooling and Heat Management: Implementing effective cooling systems or heat
management strategies can help dissipate excess heat and maintain operating
temperatures within acceptable limits.
 Proper Maintenance: Regular inspection, lubrication, and maintenance of
equipment are essential for preventing excessive friction and wear under high-
temperature conditions.
By considering these factors and implementing appropriate mitigation measures,
it is possible to minimize the detrimental effects of friction and wear in high-
temperature environments.
Friction and wear at high speeds
Friction and wear at high speeds present unique challenges due to increased
contact forces, temperature rise, and material deformation rates. Here's how
friction and wear are influenced by high speeds:
1. Contact Pressure and Temperature: At high speeds, the contact pressure
between mating surfaces increases due to the dynamic loading. This elevated
pressure can lead to higher localized temperatures at the contact interface due to
frictional heating. The combination of high pressure and temperature can
accelerate material deformation and wear processes.
2. Thermal Effects: Frictional heat generated at high speeds can cause thermal
expansion and softening of materials, potentially altering their mechanical
properties and surface characteristics. Thermal effects can exacerbate wear
mechanisms such as adhesive wear, abrasive wear, and surface fatigue.
3. Lubrication Challenges: Lubrication becomes crucial at high speeds to reduce
friction and dissipate heat generated at the contact interface. However, achieving
effective lubrication can be challenging due to the reduced time available for the
lubricant to flow into the contact zone and form a protective film. Boundary
lubrication regimes, where direct metal-to-metal contact occurs, become more
prevalent at high speeds, increasing the risk of wear.
4. Surface Fatigue: High-speed operation can induce surface fatigue mechanisms
such as rolling contact fatigue, micro-pitting, and spalling. These fatigue
processes are often influenced by the repetitive loading cycles experienced by
contacting surfaces at high speeds, leading to crack initiation and propagation.
5. Material Selection: The choice of materials becomes critical at high speeds to
withstand the mechanical and thermal stresses experienced during operation.
High-speed applications may require materials with high strength, good fatigue
resistance, and thermal stability to minimize wear and ensure reliable
performance.
6. Dynamic Effects: Dynamic factors such as vibration, resonance, and instabilities
can influence friction and wear behavior at high speeds. These dynamic effects
can lead to changes in contact conditions, altering wear mechanisms and surface
damage patterns.
To address friction and wear at high speeds, several strategies can be employed:
 Advanced Lubrication Systems: Implementing high-performance lubrication
systems, such as circulating oil systems or air/oil mist lubrication, can provide
effective lubrication and cooling at high speeds.
 Surface Treatments: Applying surface treatments such as coatings, platings, or
surface modifications can improve wear resistance and reduce friction under high-
speed conditions.
 Precision Design and Manufacturing: Designing components with precision
tolerances and surface finishes can help minimize dynamic instabilities and
reduce wear at high speeds.
 Monitoring and Maintenance: Regular monitoring of equipment condition and
performance, along with proactive maintenance practices, can help identify and
address wear-related issues before they escalate.
By understanding the unique challenges associated with friction and wear at high
speeds and implementing appropriate mitigation measures, it is possible to
achieve reliable and efficient operation in high-speed applications.
Friction and wear at high loads
Friction and wear at high loads can be significant, often leading to accelerated
material degradation and reduced component lifespan. Here are some key factors
to consider:
1. Increased Contact Pressure: High loads result in higher contact pressures
between mating surfaces. This elevated pressure can cause plastic deformation,
surface roughening, and increased frictional forces at the contact interface.
2. Material Deformation and Flow: Under high loads, materials may undergo
plastic deformation, particularly at asperity contact points. This deformation can
lead to the transfer of material between surfaces, promoting adhesive wear and
surface damage.
3. Abrasive Wear: High loads can cause abrasive particles or contaminants present
in the environment to become trapped between mating surfaces. This abrasive
action can accelerate material removal and wear, particularly in sliding or rolling
contact applications.
4. Fatigue Wear: High loads can induce fatigue wear mechanisms, such as spalling,
cracking, and fretting, particularly in cyclic loading conditions. These fatigue
processes can lead to surface damage and component failure over time.
5. Lubrication Challenges: Effective lubrication becomes crucial at high loads to
reduce friction and minimize wear. However, achieving sufficient lubrication can
be challenging due to the high contact pressures and the potential for lubricant
film breakdown or squeeze-out under load.
6. Material Selection: Choosing materials with high strength, hardness, and wear
resistance is essential for withstanding high loads. Materials such as hardened
steels, ceramics, and certain polymers are commonly used in high-load
applications to minimize wear and deformation.
7. Surface Treatments: Surface treatments such as nitriding, carburizing, and
coatings can improve wear resistance and reduce friction under high-load
conditions. These treatments can enhance surface hardness, reduce adhesion,
and provide a protective barrier against wear.
To address friction and wear at high loads, several strategies can be employed:
 Load Distribution: Designing components with optimized load distribution can
help reduce localized contact pressures and minimize wear. This can be achieved
through proper bearing design, surface profiling, and the use of load-bearing
elements such as rollers or balls.
 Lubrication Optimization: Selecting lubricants with high load-carrying capacity
and film strength is crucial for effective lubrication under high loads. Extreme
pressure (EP) additives or solid lubricants can help provide additional protection
against wear.
 Maintenance and Monitoring: Regular inspection and maintenance of equipment
are essential for identifying wear-related issues early and implementing corrective
measures. Monitoring techniques such as vibration analysis, thermography, and
oil analysis can help detect abnormal wear patterns and potential failure modes.
 Material and Design Optimization: Continuously improving material properties
and optimizing component design can help mitigate wear and prolong component
life under high-load conditions. This may involve material selection, heat
treatment, surface engineering, and fatigue analysis.
By addressing these factors and implementing appropriate mitigation measures, it
is possible to minimize friction and wear at high loads, thereby improving
component reliability and longevity in demanding applications.
Thermal considerations in sliding contact.
Thermal considerations in sliding contact play a crucial role in various
engineering applications, especially in mechanical systems involving sliding or
rubbing components like bearings, seals, brakes, and gears.
When two surfaces slide against each other, frictional forces generate heat due
to the conversion of mechanical energy into thermal energy. Managing this
heat buildup is essential to prevent excessive wear, material degradation, and
potential system failure. Several factors influence thermal considerations in
sliding contact:
1. Material Properties: The choice of materials greatly impacts the thermal behavior
of sliding contacts. Thermal conductivity, specific heat capacity, and coefficient of
friction are essential properties to consider. Materials with high thermal
conductivity dissipate heat more efficiently, while those with low coefficients of
friction experience less heat generation.
2. Contact Pressure: Higher contact pressures between sliding surfaces can lead to
increased frictional heating. Proper design considerations, such as optimizing
surface geometry and lubrication, can help mitigate this effect.
3. Sliding Speed: Faster sliding speeds typically result in greater heat generation
due to increased frictional forces. Managing sliding speeds through design
modifications or lubrication techniques can help control heat buildup.
4. Lubrication: Lubricants reduce friction between sliding surfaces, thereby
reducing heat generation. Proper lubrication selection based on operating
conditions is critical for maintaining optimal thermal performance and preventing
excessive wear.
5. Surface Roughness: Surface roughness affects the contact area and the
magnitude of frictional forces, thereby influencing heat generation. Smoother
surfaces generally experience lower friction and heat generation compared to
rough surfaces.
6. Cooling Mechanisms: Incorporating cooling mechanisms such as air or liquid
circulation can help dissipate heat from sliding contacts. Heat sinks or fins may
also be utilized to enhance heat dissipation.
7. Thermal Management Systems: In some applications, dedicated thermal
management systems like heat exchangers or coolant circulation systems may be
necessary to regulate temperatures within acceptable limits.
8. Operating Environment: External factors such as ambient temperature and
humidity can influence thermal behavior in sliding contacts. Extreme
environmental conditions may necessitate additional thermal protection
measures.
9. Material Wear and Degradation: Elevated temperatures can accelerate material
wear and degradation in sliding contacts. Understanding the thermal effects on
material properties is essential for predicting component lifespan and reliability.
10. Simulation and Analysis: Computational tools like finite element analysis
(FEA) or computational fluid dynamics (CFD) can be employed to model and
analyze thermal behavior in sliding contacts, aiding in the optimization of design
parameters for improved performance and reliability.
In summary, thermal considerations in sliding contact are multifaceted and
require careful attention to material selection, design optimization, lubrication,
and cooling strategies to ensure efficient operation and longevity of mechanical
systems.
Part-A
1. Enumerate the purpose of surface engineering in industries [RE, CO1]
Surface engineering in industries aims to improve the
performance of materials by enhancing their surface
properties such as hardness, wear resistance, corrosion
resistance, and surface finish.
2. What are the various thermal considerations in sliding
contact.
[RE, CO1]
In sliding contact, friction between surfaces generates heat
due to mechanical energy conversion. The amount of heat
produced depends on factors like sliding speed, contact
pressure, surface roughness, and lubrication.
3. Discuss the role of friction in extreme conditions [RE, CO1]
Friction in extreme conditions happens when things rub
together under intense pressure, speed, or temperature.
In extreme situations, friction generates a lot of heat, which
can damage parts or cause them to wear out faster
4. Enumerate the various roughness parameters [RE, CO1]
1. Ra (Arithmetic Average Roughness):
2. Rz (Average Maximum Height):
3. Rp (Maximum Peak Height) and Rv (Maximum Valley
Depth):
4. Rq (Root Mean Square Roughness):
5. Rt (Total Roughness):
5. Define surface feature [RE, CO1]
A surface feature refers to any distinctive characteristic,
irregularity, or pattern present on the surface of an object.
6. List the types of surface features [RE, CO1]
These features can include grooves, ridges, textures,
scratches, pits, or any other physical attributes that are
observable or measurable on the surface.
7. What is meant by surface topography? [RE, CO1]
Surface topography refers to the three-dimensional
structure or landscape of a surface, including its
height variations, roughness, and texture.
8. Compare SEM and AFM [UN, CO1]
SEM (Scanning Electron Microscopy) uses a focused beam
of electrons to generate high-resolution images of sample
surfaces, providing detailed topographical and
compositional information.
AFM (Atomic Force Microscopy), on the other hand, employs
a sharp probe to scan the surface of a sample, measuring
forces between the probe and sample to create topographic
maps with atomic-scale resolution.
9. Enumerate the causes of friction [RE, CO1]
Adhesion
Surface Roughness
Deformation
Surface Properties
Temperature
Lubrication:
10. Define friction [RE, CO1]
Friction is the force that opposes the relative motion or
tendency of motion between two surfaces in contact
11. Construct a block diagram showing scope of surface
engineering
[RE, CO1]
12. Define surface energy [RE, CO1]
Surface energy refers to the excess energy per unit area
present at the surface of a material compared to its interior.
It arises due to unbalanced intermolecular forces at the
surface, leading to surface tension.
13. Enumerate the common factors leading to the deterioration [RE, CO1]
of surfaces
Wear: Wear is the gradual loss of material from a surface
due to mechanical action, such as rubbing, abrasion, or
erosion.
Corrosion: Corrosion is the degradation of a material's
surface due to chemical reactions with the environment.
14. Define Stick-slip Phenomenon [RE, CO1]
The stick-slip phenomenon refers to the jerky or
intermittent motion observed when two surfaces in contact
alternate between sticking and slipping during relative
motion.
15. List out the friction properties of metals [RE, CO1]
Metals typically exhibit relatively high coefficients of friction
when in contact with other materials.
This property can lead to significant resistance to motion,
affecting performance in sliding or rolling applications.
16. List out the friction properties of nonmetals [RE, CO1]
Nonmetals can exhibit a wide range of coefficients of friction
depending on factors such as surface roughness,
temperature, and environmental conditions.
Nonmetals often have a higher sensitivity to lubrication
compared to metals. Proper lubrication can significantly
reduce friction and wear in nonmetallic materials.
17. Define Static friction [RE, CO1]
Static friction is the force that prevents two stationary
surfaces from moving relative to each other when an
external force is applied to one of the surfaces.
18. Define Rolling Friction [RE, CO1]
Rolling friction is the resistance encountered when an object
rolls over a surface.
Rolling friction is typically lower than sliding friction.
19. What are the various causes of friction? [RE, CO1]
Adhesion
Surface Roughness
Deformation
Surface Properties
Temperature
Lubrication:
20. Define the Laws of friction [RE, CO1]
The force of friction is directly proportional to the normal
force pressing the surfaces together.
The force of friction is independent of the apparent area of
contact between the surfaces.

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CME 397 - SURFACE ENGINEERING - UNIT 1 FULL NOTES

  • 1. AAA COLLEGE OF ENGINEERING & TECHNOLOGY Accredited by NBA (CSE, ECE, EEE & MECHANICAL), (Accredited by NAAC with “A” grade) (Approved by AICTE, New Delhi & Affiliated to Anna University, Chennai) (An ISO 21001: 2018 Certified Institution) Amathur, Sivakasi - 626 005. Department of Mechanical Engineering CME397 Surface Engineering (Professional Elective) Name of the Student : Register Number : Class / Semester : III YEAR / VI SEMESTER Academic Year : 2023– 2024 Regulation : 2021 Name of the Course Instructor : M.Karthikeyan AP/MECH
  • 2. Syllabus UNIT – I SURFACES AND FRICTION Basics of surfaces features – Roughness parameters – surface measurement - Cause of friction- Laws of friction – Static friction – Rolling Friction – Stick-slip Phenomenon - Friction properties of metal and nonmetals – Friction in extreme conditions – Thermal considerations in sliding contact. UNIT – II WEAR Laws of Wear - Types of Wear mechanism – wear debris analysis - Theoretical wear models - Wear of metals and nonmetals – International standards in friction and wear measurements UNIT – III CORROSION Introduction – Types of corrosion – Factors influencing corrosion – Testing of corrosion – In-service monitoring, Simulated service, Laboratory testing – Prevention of Corrosion – Material selection, Alteration of environment, Design, Cathodic and Anodic Protection, Corrosion inhibitors UNIT – IV SURFACE TREATMENTS Surface properties – Hydrophobic – Super hydrophobic – Hydrophilic - surface metallurgy –Surface coating Techniques – PVD – CVD – Physical CVD – Ion implantation – Surface welding – Thermal spraying – Laser surface hardening and alloying - New trends in coating technology – DLC – CNC – Thick coatings – Nanoengineered coatings – Other coatings, Corrosion resistant coatings UNIT – V ENGINEERING MATERIALS Introduction – High and low friction materials - Advanced alloys – Super alloys, Titanium alloys, Magnesium alloys, Aluminium alloys, and Nickel based alloys – Ceramics – Polymers – Biomaterials – Bio Tribology -Nano Tribology TOTAL:45 PERIODS
  • 3. UNIT – I SURFACES AND FRICTION Basics of surfaces features – Roughness parameters – surface measurement - Cause of friction- Laws of friction – Static friction – Rolling Friction – Stick-slip Phenomenon - Friction properties of metal and nonmetals – Friction in extreme conditions – Thermal considerations in sliding contact. Basics of surfaces features  Surface features refer to the characteristics, irregularities, and patterns present on the outermost layer of a material or object.  Understanding and characterizing surface features are essential for optimizing material performance, enhancing product functionality, improving manufacturing processes, and ensuring quality control in various industries and applications.  Techniques such as scanning electron microscopy (SEM), atomic force microscopy (AFM), profilometry, and optical microscopy are commonly used to analyze and quantify surface features at different length scales.  Some fundamental aspects of surface features are 1. Topography:  Surface topography refers to the three-dimensional structure or landscape of a surface, including its height variations, roughness, and texture.  Topographic features can range from microscale to macroscale, and they play a crucial role in determining the functional properties of a surface, such as friction, adhesion, wear resistance, and optical properties. 2. Roughness:
  • 4.  Surface roughness refers to the irregularities or deviations from an ideal flat surface on a microscopic scale.  Roughness can be quantified using parameters such as Ra (Arithmetic Average Roughness), Rz (Average Maximum Height), Rq (Root Mean Square Roughness), and others.  It influences the appearance, feel, and performance of surfaces, impacting factors such as friction, lubrication, and contact mechanics. 3. Texture:  Surface texture encompasses the arrangement and distribution of microscale features on a surface, including patterns, grains, grooves, and ridges.  Texture affects the visual appearance, tactile feel, and functionality of surfaces.  It is often characterized by parameters such as spatial frequency, orientation, and amplitude of surface features. 4. Waviness:  Surface waviness refers to the broader, low-frequency undulations or periodic variations in surface roughness.  Waviness typically occurs on a larger scale than roughness features and can be caused by factors such as machining processes, tool vibrations, or material properties.  It is important to distinguish waviness from roughness when analyzing surface profiles. 5. Defects:
  • 5.  Surface defects are irregularities or imperfections on a surface that deviate from the desired or intended structure.  Common surface defects include scratches, pits, cracks, porosity, and contamination.  Defects can affect the structural integrity, functionality, and aesthetic quality of surfaces, making them a crucial consideration in quality control and inspection processes. 6. Anisotropy:  Surface anisotropy refers to the directional dependence of surface properties or features.  Anisotropic surfaces exhibit different characteristics or behaviors depending on the direction of measurement or observation.  Anisotropy can arise from factors such as material processing methods, crystallographic orientation, or surface treatments. 7. Tribological Properties:  Surface features play a significant role in determining the tribological properties of materials, including friction, wear, and lubrication behavior.  The interaction between surface asperities, roughness, and lubricants influences the performance and durability of mechanical components, coatings, and interfaces.
  • 6. Roughness parameters 1. Traversing Length:  It is denoted by LT.  The traversing length refers to the distance over which the stylus travels along the surface. 2. Assessment Length:  It is denoted by LM.  In roughness measurement, the assessment length refers to the segment of the surface profile over which roughness parameters are calculated and evaluated. 3. Sampling Length:  It is the length of a section inside the assessment length.  It is equivalent to the wavelength of the filter.  It is denoted by LV. 4. Ra (Arithmetic Average Roughness):
  • 7.  Ra represents the arithmetic average of the absolute values of the profile heights over the evaluation length.  It provides a general indication of the height deviations of the surface. 5. Rz (Average Maximum Height):  Rz measures the average of the heights of the five highest peaks and the five deepest valleys in the sampling length.  It provides information about the extremes of the surface roughness profile. 6. Rp (Maximum Peak Height) and Rv (Maximum Valley Depth):  Rp and Rv represent the maximum peak height and the maximum valley depth, respectively, within the evaluation length. 7. Rq (Root Mean Square Roughness):  Rq is the square root of the arithmetic mean of the squares of the profile heights within the evaluation length.  It provides a measure of the root-mean-square deviation of the surface roughness profile. 8. Rt (Total Roughness):
  • 8.  Rt represents the difference between the highest peak and the deepest valley within the evaluation length.  It provides information about the overall height variation of the surface. 9. Rmax (Maximum Height):  Rmax is the height of the highest peak within the evaluation length.  It represents the maximum height deviation of the surface. 10. Rmr (Material Ratio):  Rmr is the ratio of the material volume above the mean line to the total evaluation length.  It characterizes the predominant material ratio of the surface. 11. S (Lay):  S is a parameter that describes the predominant direction of the surface texture.  It can be measured as the average spacing between the surface features. All these parameters are typically determined using profilometers or other specialized instruments capable of measuring surface profiles. Different applications may require different parameters depending on the specific surface characteristics that are of interest.
  • 9. Surface measurement  Surface measurement refers to the process of quantitatively assessing various characteristics of a surface, such as roughness, topography, texture, and morphology.  These measurements are crucial for evaluating the quality, functionality, and performance of surfaces in diverse fields including manufacturing, engineering, materials science, and biology.  Surface measurement techniques are selected based on factors such as the desired resolution, measurement speed, sample properties, and the specific features of interest.  Here are some common methods used for surface measurement: 1. Contact Profilometry:  Contact profilometry involves using a stylus or probe to physically trace the surface profile.  As the probe moves across the surface, it records the vertical displacement, allowing for the calculation of surface roughness parameters such as Ra, Rz, and Rq.  Contact profilometers are versatile instruments suitable for a wide range of surfaces and materials. 2. Non-contact Profilometry:
  • 10.  Non-contact profilometry methods, such as optical profilometry and confocal microscopy, use optical principles to measure surface topography without physically touching the surface.  These techniques offer high resolution, fast data acquisition, and non- destructive measurement capabilities, making them suitable for delicate or soft materials. 3. Atomic Force Microscopy (AFM):  AFM is a high-resolution imaging technique that uses a sharp tip mounted on a cantilever to scan the surface in a raster pattern.  By measuring the deflection of the cantilever as it interacts with the surface, AFM can generate three-dimensional images with nanometer-scale resolution.  AFM is particularly useful for studying nanoscale features and surface properties of materials. 4. Scanning Electron Microscopy (SEM):  SEM provides detailed images of surface morphology and topography by scanning the surface with a focused beam of electrons.  SEM offers high magnification capabilities and can reveal fine surface structures and features with sub-micron resolution.  It is widely used for characterizing materials in materials science, geology, and biology. 5. Optical Microscopy:
  • 11.  Optical microscopy is a versatile and widely used technique for visualizing surface features and structures.  Depending on the configuration and magnification of the microscope, optical microscopy can provide detailed images of surface morphology, texture, and defects.  Advanced techniques such as polarized light microscopy offer enhanced contrast and visualization capabilities. 6. Surface Roughness Testers:  Surface roughness testers, also known as surface roughness meters or profilometers, are portable instruments designed specifically for measuring surface roughness parameters.  These devices typically use a skid-mounted stylus or a non-contact sensor to scan the surface and provide real-time roughness measurements on-site. 7. White Light Interferometry (WLI):  WLI is an optical technique that utilizes the interference pattern generated by white light reflected from the surface to measure surface height variations with sub-nanometer resolution.  WLI is capable of producing high-resolution, three-dimensional surface maps and is widely used in metrology and semiconductor industry applications.
  • 12. Cause of friction  Friction is the force that opposes the relative motion or tendency of motion between two surfaces in contact.  It is caused by various microscopic and macroscopic interactions between the contacting surfaces.  Understanding the causes of friction is essential for designing materials, components, and systems with optimized tribological properties.  By mitigating frictional losses and wear, engineers can improve the efficiency, reliability, and longevity of mechanical systems in various applications.  The primary causes of friction include: 1. Adhesion:  Adhesion is the phenomenon where molecules from the surfaces in contact attract each other, leading to the formation of molecular bonds across the interface.  These adhesive forces create resistance to sliding or motion between the surfaces.  Adhesion is particularly significant in materials with high surface energy or when the surfaces are in close contact. 2. Surface Roughness:  Surface roughness refers to the irregularities or asperities present on the surfaces in contact.
  • 13.  When two surfaces slide against each other, the asperities interlock, causing resistance to motion.  The degree of surface roughness influences the magnitude of friction, with rougher surfaces typically exhibiting higher friction coefficients. 3. Deformation:  When two surfaces are pressed together, they deform at the contact points due to the applied load.  Deformation increases the real contact area between the surfaces, leading to higher frictional forces.  The extent of deformation depends on the mechanical properties of the materials, such as hardness, elasticity, and plasticity. 4. Surface Properties:  The chemical composition, surface energy, and surface treatments of materials influence their frictional behavior.  For example, materials with higher surface energy tend to exhibit stronger adhesive forces and higher friction coefficients.  Additionally, surface treatments such as lubrication or surface coatings can modify the frictional characteristics of materials. 5. Temperature:  Frictional forces can generate heat at the interface between two sliding surfaces.  Increased temperature can affect the properties of the materials and the nature of surface interactions, leading to changes in friction behavior.
  • 14.  In some cases, elevated temperatures may reduce friction by promoting lubrication or by altering material properties. 6. Lubrication:  Lubrication involves the introduction of a lubricant between two sliding surfaces to reduce friction and wear.  Lubricants can act as a barrier between the surfaces, minimizing direct contact and reducing adhesive forces.  Different types of lubricants, such as oils, greases, and solid lubricants, are used depending on the application requirements and operating conditions. 7. Velocity:  The relative velocity between two surfaces affects the magnitude and nature of frictional forces.  The friction may decrease with increasing velocity, particularly in regimes where fluid lubrication becomes more effective.
  • 15. Laws of friction  The laws of friction describe the fundamental principles governing the interaction between two solid surfaces in contact.  These laws were first formulated by Leonardo da Vinci and later refined by Amontons and Coulomb.  The laws of friction can be summarized as follows: 1. Coulomb's Law of Friction:  Coulomb's law states that the force of friction between two surfaces is proportional to the normal force pressing the surfaces together.  Mathematically, Coulomb's law can be expressed as Ff=μN, where:  Ff is the force of friction.  μ is the coefficient of friction, which is a dimensionless constant representing the frictional characteristics of the surfaces.  N is the normal force exerted perpendicular to the surfaces. 2. Direction of Friction:  The force of friction Ff always acts parallel to the surfaces in contact and opposes the relative motion or tendency of motion between the surfaces.  The direction of friction is determined by the direction of the applied force or motion. 3. Static Friction:  Static friction refers to the resistance to motion experienced by stationary objects in contact.
  • 16.  The force of static friction (Ffs) can vary and is generally equal to or less than the maximum possible static friction force, which is given by Ffs=μsN, where μs is the coefficient of static friction.  Static friction prevents the motion of an object until an external force overcomes it. 4. Kinetic Friction:  Kinetic friction, also known as sliding friction or dynamic friction, refers to the resistance to motion experienced by objects in motion relative to each other.  The force of kinetic friction (Ffk) is generally less than the maximum possible static friction force and is given by Ffk=μkN, where μk is the coefficient of kinetic friction.  Kinetic friction opposes the relative motion between surfaces and acts to slow down moving objects. 5. Dependence on Surface Roughness and Material Properties:  The coefficients of friction (μ) depend on the nature of the surfaces in contact, including their roughness, surface texture, and material properties.  Smooth surfaces typically exhibit lower coefficients of friction compared to rough surfaces.  The coefficients of friction can vary depending on factors such as surface lubrication, temperature, and contact pressure. These laws of friction provide a foundation for understanding and predicting the behavior of frictional forces in various mechanical systems, influencing the design, operation, and maintenance of machinery and structures.
  • 17. Static friction Static friction is the resistance force that prevents two stationary objects from moving relative to each other when an external force is applied. It acts parallel to the surfaces in contact and opposes the impending motion or tendency of motion between the objects. Here are some key points about static friction: 1. Prevents Motion: Static friction arises when there is an external force acting on an object but the object remains stationary. The force of static friction precisely balances the applied force, preventing motion. 2. Maximum Limit: The force of static friction can vary and is generally equal to or less than the maximum possible static friction force. This maximum static friction force is determined by the coefficient of static friction (μs) multiplied by the normal force (N) pressing the surfaces together: Ffs=μsN. 3. Dependent on Applied Force: The force of static friction increases proportionally with the magnitude of the applied force until it reaches its maximum value. If the applied force exceeds the maximum static friction force, the object will start moving, and kinetic friction will take over. 4. Dependent on Surface Characteristics: The coefficient of static friction (μs) depends on the nature of the surfaces in contact, including their roughness, surface texture, and material properties. Smooth surfaces typically have lower coefficients of static friction compared to rough surfaces. 5. No Motion, No Wear: Since static friction prevents motion, it does not result in wear or surface damage between stationary objects. However, it contributes to the wear when the objects transition from static to kinetic friction.
  • 18. 6. Applications: Static friction is crucial in various applications, such as keeping objects in place on surfaces (e.g., preventing a book from sliding off a table), maintaining traction between tires and roads, and allowing machinery to start and stop smoothly without slipping. Understanding static friction is essential in engineering and everyday life, as it influences the design of structures, machinery, and transportation systems, ensuring stability, safety, and efficiency.
  • 19. Rolling Friction  Rolling friction, also known as rolling resistance, is the resistance force that occurs when one object rolls over another.  Unlike sliding friction, which occurs when two surfaces slide past each other, rolling friction involves the interaction between a rolling object and the surface over which it rolls.  Understanding rolling friction is essential in the design and operation of vehicles, machinery, and other systems where rolling motion is involved. Minimizing rolling friction can improve efficiency, reduce energy consumption, and enhance performance.  Here are some key points about rolling friction: 1. Mechanism:  Rolling friction arises due to deformation and interaction between the rolling object and the surface it rolls on.  As the object rolls, there is a region of contact between the object and the surface, where deformation and adhesion occur. 2. Direction:  Rolling friction acts parallel to the surface and opposes the motion of the rolling object.  It acts in the direction opposite to the direction of rolling motion. 3. Dependence on Surface Properties:
  • 20.  Rolling friction depends on various factors, including the roughness, texture, and material properties of the rolling object and the surface it rolls on.  Smoother surfaces generally experience lower rolling friction. 4. Dependence on Load:  Rolling friction is influenced by the weight or load pressing the rolling object against the surface.  Heavier objects typically experience higher rolling friction. 5. Reduced Energy Loss:  Compared to sliding friction, rolling friction results in less energy loss because the object deforms and rebounds during each rotation, rather than continuously sliding and dissipating energy as heat. 6. Applications:  Rolling friction is encountered in various everyday situations, such as when a vehicle rolls on a road, a ball rolls on the ground, or a wheel rolls on a surface.  It is also a significant factor in the efficiency of machinery, transportation systems, and mechanical systems involving rotating components. 7. Coefficient of Rolling Friction:  Similar to sliding friction, rolling friction can be quantified by a coefficient of rolling friction (μr), which represents the ratio of the rolling friction force to the normal force pressing the rolling object against the surface.
  • 21. Stick-slip Phenomenon  https://www.tribonet.org/news/general-topics/stick-slip-phenomenon/ In tribology, the stick-slip phenomenon refers to the irregular motion that occurs when two surfaces slide against each other, alternating between periods of sticking and slipping.  This phenomenon is of significant interest in tribology because it directly impacts friction, wear, and the overall performance of mechanical systems.  Here's how the stick-slip phenomenon manifests in tribological contexts: 1. Interfacial Friction:  At the interface between two surfaces, there's a force resisting their relative motion, known as friction.  When the applied force exceeds a certain threshold, the surfaces overcome static friction and begin to move.  However, due to irregularities in surface topography, the surfaces don't move smoothly; they momentarily stick together before slipping.  This sticking and slipping cycle repeats, causing the jerky motion characteristic of stick-slip behavior.
  • 22. 2. Energy Dissipation:  During the sticking phase, energy accumulates in the form of elastic deformation and interfacial adhesion.  When the applied force exceeds the threshold, this stored energy is suddenly released during slipping, leading to rapid motion and often generating vibrations and noise.  This energy dissipation contributes to wear and can affect the efficiency and performance of tribological systems. 3. Influence of Lubrication:  Lubricants play a crucial role in tribology by reducing friction and wear between sliding surfaces.  In the context of stick-slip, lubrication can help mitigate the phenomenon by providing a fluid film that separates the surfaces and reduces the likelihood of them sticking together.  Proper lubrication selection and maintenance are essential for minimizing stick-slip and ensuring smooth operation in mechanical systems. 4. Surface Roughness and Contact Mechanics:  Surface roughness and the nature of surface interactions significantly influence stick-slip behavior.  Rough surfaces tend to have more frequent and pronounced stick-slip motion compared to smoother surfaces.  Additionally, the contact mechanics at the interface, including adhesion and plowing effects, affect the magnitude and duration of stick and slip events.
  • 23. 5. Control and Mitigation:  Engineers employ various techniques to control and mitigate stick-slip in tribological systems.  This may involve surface treatments to reduce roughness and enhance lubrication effectiveness, optimization of operating conditions (e.g., load, speed), and the design of damping mechanisms to suppress vibrations associated with stick-slip motion. Understanding and effectively managing stick-slip phenomena are crucial for improving the reliability, durability, and efficiency of mechanical systems across diverse industrial applications, ranging from automotive components to manufacturing machinery and precision equipment. Tribologists continuously research and develop strategies to better understand, predict, and control stick- slip behavior to address the challenges posed by friction and wear in real-world applications.
  • 24. Friction properties of metals Metals exhibit different friction properties depending on factors like surface roughness, lubrication, temperature, and load. Here are some key points: • Static Friction: The friction between stationary surfaces. Metals can have high static friction due to interlocking irregularities on their surfaces • Kinetic Friction: The friction between moving surfaces. Metals generally have lower kinetic friction compared to static friction but can still vary based on factors like surface finish and lubrication. • Surface Roughness: Rough surfaces create more friction due to increased contact points. Polishing or smoothing metal surfaces reduces friction by minimizing contact points. • Lubrication: Adding lubricants like oils or greases can significantly reduce friction between metal surfaces by creating a barrier between them. • Temperature: Friction between metals typically decreases with increasing temperature due to reduced intermolecular forces at higher temperatures. • Load: Heavier loads can increase friction between metal surfaces due to higher contact pressures, especially in the case of rough surfaces. • Metal Type: Different metals have varying friction properties. For example, softer metals like lead or aluminum generally have lower friction coefficients compared to harder metals like steel. • Understanding these factors helps engineers optimize friction properties for specific applications, such as machinery, automotive components, or manufacturing processes.
  • 25. Friction properties of nonmetals • Friction properties of non-metals, such as plastics, ceramics, and polymers, differ from those of metals due to their distinct material characteristics. Here's an overview: • Coefficient of Friction: Non-metals often have lower coefficients of friction compared to metals, meaning they typically require less force to initiate motion between surfaces • Surface Roughness: Similar to metals, surface roughness influences friction in non-metals. Rough surfaces create more friction, while smoother surfaces reduce friction. • Lubrication: Non-metals can benefit from lubrication to further reduce friction. Lubricants like silicone-based oils or greases are commonly used with non-metal surfaces to minimize friction and wear. • Temperature Sensitivity: Some non-metals, like plastics, may experience changes in friction properties with temperature variations. For example, certain polymers can become softer and exhibit lower friction at higher temperatures. • Wear Resistance: Non-metals generally have lower wear resistance compared to metals, which can affect their friction properties over time. Surface treatments or coatings may be applied to enhance wear resistance and maintain consistent friction levels. • Chemical Compatibility: Non-metals may exhibit specific friction behaviors in different chemical environments. For example, exposure to certain chemicals can alter the surface properties of polymers, affecting their friction characteristics. • Deformation: Non-metals can deform more easily under load compared to metals. This deformation can influence friction by changing the contact area and surface roughness between mating surfaces. • Understanding these properties is crucial for designing components and systems where non-metallic materials are used, such as in automotive components, consumer electronics, biomedical devices, and various industrial applications.
  • 26. Friction in extreme conditions Friction in extreme conditions happens when things rub together under intense pressure, speed, or temperature. This can occur in machinery, engines, or even in space where conditions are harsh. In extreme situations, friction generates a lot of heat, which can damage parts or cause them to wear out faster. Engineers tackle this by using special materials that can handle high temperatures and pressures, and they often apply lubricants to reduce friction and heat. Additionally, cooling systems may be installed to prevent overheating. Managing friction in extreme conditions is crucial to ensure machines and systems operate smoothly and safely. Friction and wear under vacuum Friction and wear under vacuum conditions pose unique challenges compared to normal atmospheric conditions. In vacuum environments, such as those found in space or in certain industrial processes, there's typically a lack of air or other gases that can act as lubricants or provide cooling. This absence of lubrication and cooling mechanisms can lead to increased friction and wear between surfaces in contact. One of the main issues is that without a lubricant, surfaces can stick together more readily, leading to higher friction forces. This can cause parts to wear out faster or even seize up altogether. Furthermore, without air to dissipate heat, the heat generated by friction can't easily escape, potentially leading to overheating and thermal damage to components. To address these challenges, engineers often use specialized materials that have low friction coefficients and high resistance to wear, even in vacuum environments. They may also design components with surface coatings or treatments to reduce friction and wear. In some cases, alternative lubrication methods, such as solid lubricants or dry lubricants, may be used that don't rely on the presence of air. These lubricants
  • 27. can provide a protective layer between surfaces even in the absence of atmospheric gases. Overall, managing friction and wear under vacuum conditions requires careful consideration of materials, lubrication methods, and design strategies to ensure the reliable operation of components and systems in these challenging environments. Friction and wear under low temperatures Friction and wear under low temperatures can present unique challenges due to changes in material properties and lubricant behavior. Here are some key points to consider: 1. Material Properties: At low temperatures, materials may become more brittle and less ductile. This can lead to increased susceptibility to cracking and fracture under mechanical stress. Additionally, some materials may experience changes in their coefficient of friction at low temperatures. 2. Lubricant Viscosity: Many lubricants experience an increase in viscosity as temperature decreases. This can affect their ability to flow and provide adequate lubrication between moving parts. In extreme cases, lubricants may solidify or form gel-like structures, reducing their effectiveness. 3. Boundary Lubrication: Under low temperatures, the formation of an effective lubricating film between contacting surfaces may be hindered. This can result in higher levels of boundary lubrication, where direct metal-to-metal contact occurs, leading to increased friction and wear. 4. Surface Roughness: Cold temperatures can exacerbate the effects of surface roughness on friction and wear. Microscopic asperities on surfaces may become more pronounced, increasing the likelihood of abrasive wear and surface damage. 5. Material Compatibility: Some materials may undergo phase changes or dimensional changes at low temperatures, affecting their compatibility with other materials in contact. Differential thermal contraction between materials can also lead to increased stress at their interfaces, promoting wear. 6. Cryogenic Conditions: In extremely low temperatures, such as those encountered in cryogenic applications, conventional lubricants may not be suitable. Specialized lubricants designed for use in cryogenic environments are often required to maintain adequate lubrication and prevent excessive wear.
  • 28. To mitigate friction and wear under low temperatures, it's essential to select materials and lubricants that are suitable for the operating conditions. This may involve using materials with improved low-temperature toughness, selecting lubricants with low pour points and good flow properties at low temperatures, and employing surface treatments or coatings to reduce friction and wear. Additionally, proper equipment design and maintenance practices can help minimize the effects of low temperatures on friction and wear. Friction and wear under high temperatures Friction and wear under high temperatures can also present significant challenges, often requiring specialized materials, lubricants, and operating conditions. Here are some key considerations: 1. Thermal Expansion: At high temperatures, materials tend to expand, which can affect the clearances and tolerances between moving parts. Differential thermal expansion between mating surfaces can lead to increased contact pressures and accelerated wear. 2. Softening and Melting: High temperatures can cause materials to soften or even melt, reducing their strength and increasing their susceptibility to deformation and surface damage. This can result in increased rates of wear, particularly in applications involving high contact pressures or sliding velocities. 3. Oxidation and Degradation: Many materials undergo oxidative degradation at high temperatures, leading to changes in their surface properties and increased friction and wear. Oxidation can result in the formation of oxides, which may act as abrasive particles or promote adhesive wear between sliding surfaces. 4. Lubricant Degradation: Lubricants can degrade at high temperatures, losing their viscosity, thermal stability, and lubricating properties. Oxidation, thermal breakdown, and evaporation can all contribute to lubricant degradation, leading to increased friction and wear. 5. Surface Hardening: In some cases, high temperatures can induce surface hardening of materials through processes such as diffusion, precipitation, or transformation hardening. While surface hardening can improve wear resistance, it may also increase friction and promote abrasive wear if not properly controlled. 6. Thermal Runaway: In extreme cases, such as in high-speed or heavy-load applications, high temperatures can lead to thermal runaway, where frictional
  • 29. heat generation exceeds the heat dissipation capacity of the system. This can result in localized melting, welding, or catastrophic failure of components. To address friction and wear under high temperatures, several strategies can be employed:  High-Temperature Materials: Selecting materials with high-temperature stability, such as heat-resistant alloys or ceramics, can help mitigate wear at elevated temperatures.  Specialized Lubricants: Using lubricants specifically formulated for high- temperature applications, such as synthetic oils or solid lubricants, can help maintain lubrication effectiveness and reduce friction and wear.  Surface Treatments: Applying coatings or surface treatments, such as nitriding, ceramic coatings, or diamond-like carbon (DLC) coatings, can improve surface hardness and wear resistance at high temperatures.  Cooling and Heat Management: Implementing effective cooling systems or heat management strategies can help dissipate excess heat and maintain operating temperatures within acceptable limits.  Proper Maintenance: Regular inspection, lubrication, and maintenance of equipment are essential for preventing excessive friction and wear under high- temperature conditions. By considering these factors and implementing appropriate mitigation measures, it is possible to minimize the detrimental effects of friction and wear in high- temperature environments. Friction and wear at high speeds Friction and wear at high speeds present unique challenges due to increased contact forces, temperature rise, and material deformation rates. Here's how friction and wear are influenced by high speeds: 1. Contact Pressure and Temperature: At high speeds, the contact pressure between mating surfaces increases due to the dynamic loading. This elevated pressure can lead to higher localized temperatures at the contact interface due to frictional heating. The combination of high pressure and temperature can accelerate material deformation and wear processes. 2. Thermal Effects: Frictional heat generated at high speeds can cause thermal expansion and softening of materials, potentially altering their mechanical properties and surface characteristics. Thermal effects can exacerbate wear mechanisms such as adhesive wear, abrasive wear, and surface fatigue.
  • 30. 3. Lubrication Challenges: Lubrication becomes crucial at high speeds to reduce friction and dissipate heat generated at the contact interface. However, achieving effective lubrication can be challenging due to the reduced time available for the lubricant to flow into the contact zone and form a protective film. Boundary lubrication regimes, where direct metal-to-metal contact occurs, become more prevalent at high speeds, increasing the risk of wear. 4. Surface Fatigue: High-speed operation can induce surface fatigue mechanisms such as rolling contact fatigue, micro-pitting, and spalling. These fatigue processes are often influenced by the repetitive loading cycles experienced by contacting surfaces at high speeds, leading to crack initiation and propagation. 5. Material Selection: The choice of materials becomes critical at high speeds to withstand the mechanical and thermal stresses experienced during operation. High-speed applications may require materials with high strength, good fatigue resistance, and thermal stability to minimize wear and ensure reliable performance. 6. Dynamic Effects: Dynamic factors such as vibration, resonance, and instabilities can influence friction and wear behavior at high speeds. These dynamic effects can lead to changes in contact conditions, altering wear mechanisms and surface damage patterns. To address friction and wear at high speeds, several strategies can be employed:  Advanced Lubrication Systems: Implementing high-performance lubrication systems, such as circulating oil systems or air/oil mist lubrication, can provide effective lubrication and cooling at high speeds.  Surface Treatments: Applying surface treatments such as coatings, platings, or surface modifications can improve wear resistance and reduce friction under high- speed conditions.  Precision Design and Manufacturing: Designing components with precision tolerances and surface finishes can help minimize dynamic instabilities and reduce wear at high speeds.  Monitoring and Maintenance: Regular monitoring of equipment condition and performance, along with proactive maintenance practices, can help identify and address wear-related issues before they escalate. By understanding the unique challenges associated with friction and wear at high speeds and implementing appropriate mitigation measures, it is possible to achieve reliable and efficient operation in high-speed applications.
  • 31. Friction and wear at high loads Friction and wear at high loads can be significant, often leading to accelerated material degradation and reduced component lifespan. Here are some key factors to consider: 1. Increased Contact Pressure: High loads result in higher contact pressures between mating surfaces. This elevated pressure can cause plastic deformation, surface roughening, and increased frictional forces at the contact interface. 2. Material Deformation and Flow: Under high loads, materials may undergo plastic deformation, particularly at asperity contact points. This deformation can lead to the transfer of material between surfaces, promoting adhesive wear and surface damage. 3. Abrasive Wear: High loads can cause abrasive particles or contaminants present in the environment to become trapped between mating surfaces. This abrasive action can accelerate material removal and wear, particularly in sliding or rolling contact applications. 4. Fatigue Wear: High loads can induce fatigue wear mechanisms, such as spalling, cracking, and fretting, particularly in cyclic loading conditions. These fatigue processes can lead to surface damage and component failure over time. 5. Lubrication Challenges: Effective lubrication becomes crucial at high loads to reduce friction and minimize wear. However, achieving sufficient lubrication can be challenging due to the high contact pressures and the potential for lubricant film breakdown or squeeze-out under load. 6. Material Selection: Choosing materials with high strength, hardness, and wear resistance is essential for withstanding high loads. Materials such as hardened steels, ceramics, and certain polymers are commonly used in high-load applications to minimize wear and deformation. 7. Surface Treatments: Surface treatments such as nitriding, carburizing, and coatings can improve wear resistance and reduce friction under high-load conditions. These treatments can enhance surface hardness, reduce adhesion, and provide a protective barrier against wear. To address friction and wear at high loads, several strategies can be employed:  Load Distribution: Designing components with optimized load distribution can help reduce localized contact pressures and minimize wear. This can be achieved through proper bearing design, surface profiling, and the use of load-bearing elements such as rollers or balls.
  • 32.  Lubrication Optimization: Selecting lubricants with high load-carrying capacity and film strength is crucial for effective lubrication under high loads. Extreme pressure (EP) additives or solid lubricants can help provide additional protection against wear.  Maintenance and Monitoring: Regular inspection and maintenance of equipment are essential for identifying wear-related issues early and implementing corrective measures. Monitoring techniques such as vibration analysis, thermography, and oil analysis can help detect abnormal wear patterns and potential failure modes.  Material and Design Optimization: Continuously improving material properties and optimizing component design can help mitigate wear and prolong component life under high-load conditions. This may involve material selection, heat treatment, surface engineering, and fatigue analysis. By addressing these factors and implementing appropriate mitigation measures, it is possible to minimize friction and wear at high loads, thereby improving component reliability and longevity in demanding applications.
  • 33. Thermal considerations in sliding contact. Thermal considerations in sliding contact play a crucial role in various engineering applications, especially in mechanical systems involving sliding or rubbing components like bearings, seals, brakes, and gears. When two surfaces slide against each other, frictional forces generate heat due to the conversion of mechanical energy into thermal energy. Managing this heat buildup is essential to prevent excessive wear, material degradation, and potential system failure. Several factors influence thermal considerations in sliding contact:
  • 34. 1. Material Properties: The choice of materials greatly impacts the thermal behavior of sliding contacts. Thermal conductivity, specific heat capacity, and coefficient of friction are essential properties to consider. Materials with high thermal conductivity dissipate heat more efficiently, while those with low coefficients of friction experience less heat generation. 2. Contact Pressure: Higher contact pressures between sliding surfaces can lead to increased frictional heating. Proper design considerations, such as optimizing surface geometry and lubrication, can help mitigate this effect. 3. Sliding Speed: Faster sliding speeds typically result in greater heat generation due to increased frictional forces. Managing sliding speeds through design modifications or lubrication techniques can help control heat buildup. 4. Lubrication: Lubricants reduce friction between sliding surfaces, thereby reducing heat generation. Proper lubrication selection based on operating conditions is critical for maintaining optimal thermal performance and preventing excessive wear. 5. Surface Roughness: Surface roughness affects the contact area and the magnitude of frictional forces, thereby influencing heat generation. Smoother surfaces generally experience lower friction and heat generation compared to rough surfaces.
  • 35. 6. Cooling Mechanisms: Incorporating cooling mechanisms such as air or liquid circulation can help dissipate heat from sliding contacts. Heat sinks or fins may also be utilized to enhance heat dissipation. 7. Thermal Management Systems: In some applications, dedicated thermal management systems like heat exchangers or coolant circulation systems may be necessary to regulate temperatures within acceptable limits. 8. Operating Environment: External factors such as ambient temperature and humidity can influence thermal behavior in sliding contacts. Extreme environmental conditions may necessitate additional thermal protection measures. 9. Material Wear and Degradation: Elevated temperatures can accelerate material wear and degradation in sliding contacts. Understanding the thermal effects on material properties is essential for predicting component lifespan and reliability. 10. Simulation and Analysis: Computational tools like finite element analysis (FEA) or computational fluid dynamics (CFD) can be employed to model and analyze thermal behavior in sliding contacts, aiding in the optimization of design parameters for improved performance and reliability. In summary, thermal considerations in sliding contact are multifaceted and require careful attention to material selection, design optimization, lubrication, and cooling strategies to ensure efficient operation and longevity of mechanical systems.
  • 36. Part-A 1. Enumerate the purpose of surface engineering in industries [RE, CO1] Surface engineering in industries aims to improve the performance of materials by enhancing their surface properties such as hardness, wear resistance, corrosion resistance, and surface finish. 2. What are the various thermal considerations in sliding contact. [RE, CO1] In sliding contact, friction between surfaces generates heat due to mechanical energy conversion. The amount of heat produced depends on factors like sliding speed, contact pressure, surface roughness, and lubrication. 3. Discuss the role of friction in extreme conditions [RE, CO1] Friction in extreme conditions happens when things rub together under intense pressure, speed, or temperature. In extreme situations, friction generates a lot of heat, which can damage parts or cause them to wear out faster 4. Enumerate the various roughness parameters [RE, CO1] 1. Ra (Arithmetic Average Roughness): 2. Rz (Average Maximum Height): 3. Rp (Maximum Peak Height) and Rv (Maximum Valley Depth): 4. Rq (Root Mean Square Roughness): 5. Rt (Total Roughness): 5. Define surface feature [RE, CO1] A surface feature refers to any distinctive characteristic, irregularity, or pattern present on the surface of an object. 6. List the types of surface features [RE, CO1] These features can include grooves, ridges, textures, scratches, pits, or any other physical attributes that are observable or measurable on the surface. 7. What is meant by surface topography? [RE, CO1] Surface topography refers to the three-dimensional
  • 37. structure or landscape of a surface, including its height variations, roughness, and texture. 8. Compare SEM and AFM [UN, CO1] SEM (Scanning Electron Microscopy) uses a focused beam of electrons to generate high-resolution images of sample surfaces, providing detailed topographical and compositional information. AFM (Atomic Force Microscopy), on the other hand, employs a sharp probe to scan the surface of a sample, measuring forces between the probe and sample to create topographic maps with atomic-scale resolution. 9. Enumerate the causes of friction [RE, CO1] Adhesion Surface Roughness Deformation Surface Properties Temperature Lubrication: 10. Define friction [RE, CO1] Friction is the force that opposes the relative motion or tendency of motion between two surfaces in contact 11. Construct a block diagram showing scope of surface engineering [RE, CO1] 12. Define surface energy [RE, CO1] Surface energy refers to the excess energy per unit area present at the surface of a material compared to its interior. It arises due to unbalanced intermolecular forces at the surface, leading to surface tension. 13. Enumerate the common factors leading to the deterioration [RE, CO1]
  • 38. of surfaces Wear: Wear is the gradual loss of material from a surface due to mechanical action, such as rubbing, abrasion, or erosion. Corrosion: Corrosion is the degradation of a material's surface due to chemical reactions with the environment. 14. Define Stick-slip Phenomenon [RE, CO1] The stick-slip phenomenon refers to the jerky or intermittent motion observed when two surfaces in contact alternate between sticking and slipping during relative motion. 15. List out the friction properties of metals [RE, CO1] Metals typically exhibit relatively high coefficients of friction when in contact with other materials. This property can lead to significant resistance to motion, affecting performance in sliding or rolling applications. 16. List out the friction properties of nonmetals [RE, CO1] Nonmetals can exhibit a wide range of coefficients of friction depending on factors such as surface roughness, temperature, and environmental conditions. Nonmetals often have a higher sensitivity to lubrication compared to metals. Proper lubrication can significantly reduce friction and wear in nonmetallic materials. 17. Define Static friction [RE, CO1] Static friction is the force that prevents two stationary surfaces from moving relative to each other when an external force is applied to one of the surfaces. 18. Define Rolling Friction [RE, CO1] Rolling friction is the resistance encountered when an object rolls over a surface. Rolling friction is typically lower than sliding friction. 19. What are the various causes of friction? [RE, CO1] Adhesion Surface Roughness
  • 39. Deformation Surface Properties Temperature Lubrication: 20. Define the Laws of friction [RE, CO1] The force of friction is directly proportional to the normal force pressing the surfaces together. The force of friction is independent of the apparent area of contact between the surfaces.