Surface engineering info and introduction

2. • An outside part or layer of something.
• When phases (solid, liquid, gas and plasma) exist together, the boundary between two of them is
known as an interface. Surface is the term used to describe either a gas-solid or a gas-liquid interface
• Surfaces are a primary 'point of contact’
• Materials contact each other at surfaces
• Catalysis of surface mediated reactions
• Where many biological reactions occur - Perhaps
where life began
• Tribology - friction, lubrication and wear
• Most metal corrosion occurs at surfaces
A large fraction of surface atoms per unit
volume:
• 1 cubic centimetre of iron -> surface atom
10-5 %
• 1000 nm3 cube of iron -> surface atom 10%.

4. To understand the properties of the surfaces which strongly affects many applications for example
 Heterogeneous catalytic reactions (i.e. when the used catalyst is solid). Normally in these reactions the
catalyst was used as powder. We have to know:
1. The active sites on the catalyst
2. Can these sites be blocked (i.e. poisoning of the catalyst)
3. The formed intermediate species (if any)
4. The step which control the rate of reaction (i.e. diffusion of the reactants to the catalyst
surface, or the reaction kinetics or the diffusion of the products.
By understanding these things, we can modify our reaction or choosing different cheap materials as
catalyst.

5.  The processes which carried out under high pressures or temperatures (i.e. many atmospheres in
these processes the catalysts are used as fine powder and usually expensive, so have to well
understand what is going on the catalyst surface.
 In Dying of textile materials, this operation depends mainly on well understanding of the surface
properties of the fibers to chose the proper dye and getting good final products
 Corrosion, trace impurities on the metal surface strongly enhances the corrosion rate. Also,
Understanding the segregation of these impurities which might be on the surface grain boundaries or
migrate to the bulk, this also affects the corrosion and also usage of the material
 Semiconductor devices: For example
1. Metal-semiconductor junctions is strongly influenced by the tendency for chemical
interactions between the metal and semiconductor
2. The atomic structure of the semiconducting materials surface also affects the behaviour.

6. Increase the resistance to corrosion, wear, oxidation, and
sulfidation.
Enhance the mechanical properties, electrical and
electronic properties, thermal conductivity, and insulation.
Reduce the friction coefficient and improve lubrication
characteristics.
Improve aesthetics characteristics.

7.  Reduce the adverse thermal effects and mechanical effects caused
during processing.
 The loads are to be taken up by bulk as well as the (modified)
surface material.
 Often engineering properties of the bulk are deteriorated at high
temperatures while processing (for surface modification)
 So the surface modification techniques should only affect the surface
and/or near surface regions.

8.  Schematic showing
the capability of
different surface
modification
techniques with
respect to range of
modified thickness or
subsurface depth:
 A: ion implantation
 B: PVD
 C: CVD
 D: electrolytic plating
 E: electroless plating
 F: hot dipping
(galvanizing/aluminizi
ng)
 G: laser surface
alloying
 H: transformation
hardening
 I: mechanical working
 J: nitriding
 K: carbonitriding
 L: carburizing
 M: thermal spraying
 N: friction surfacing
 O: weld overlays

9.  The surface of any component
made of crystalline materials is
characterized by:
 (a) the nature of surface
irregularity which is quantified
in terms of surface roughness
 (b) the subsurface region which is
generally composed of five
distinct zones as shown
schematically in Fig

10.  • Zone I: Comprises a very thin layer of few
nanometers thickness called contamination
layer which retains absorbed gases,
hydrocarbons, moisture, etc.
 • Zone II: Constitutes impurities such as
oxides, nitrides, which are formed as a
result of interactions between atmospheric
or ambient gases and substrate surface.
 • Zone III: Involves a work-hardened layer
usually thinner than 1 μm with badly
damaged crystalline structure.

11.  • Zone IV: Consists of layer of thickness
ranging from few microns to hundreds of
micrometers with grain structure
deformed by the application of external
stresses during manufacturing or
development of residual stresses.
 • Zone V: Involves normal structure of
bulk materials as per thermal and
mechanical stresses experienced by the
material during manufacturing.

12. • Surface engineering enhances MEMS device performance and reliability
• Atomic Layer Deposition (ALD) is a precise surface engineering technique that offers
excellent conformal coating, low substrate damage, and high deposition control, making it an
ideal candidate for MEMS device fabrication.
• Surface engineering can modify the surface properties of MEMS devices to minimize adverse
reactions when used in biomedical applications.

13. MEMS APPLICATION IN AUTIMOTIVES

14. MEMS APPLICATION IN INK JET PRINTER (IT
PERIPHERALS)

15. MEMS APPLICATION IN CONSUMER ELECTRONICS
AND LIFESTYLE PRODUCTS (SMARTPHONES)

16. MEMS APPLICATION IN MILITARY

17.  MEMS are inherently small, thus offering
attractive characteristics such as reduced
size, weight, and power dissipation and
improved speed and precision compared to
their macroscopic counterparts.
 Most MEMS devices exhibit a length or width
ranging from micrometre to several hundreds
of micrometres with a thickness from sub-
micrometer up to tens of micrometres,
depending upon the fabrication technique
employed.
 Polycrystalline silicon (poly-silicon) micro-motor, achieving a diameter
of 150μm and a minimum vertical feature size on the order of a
micrometre. Figure below shows SEM micrograph of a polysilicon
microelectromechanical motor (1980s).

19.  Pressure sensors are one of the early devices realized by silicon micromachining
technologies and have become successful commercial products.
 The devices have been widely used in various industrial and biomedical
applications.
 Silicon bulk and surface micromachining techniques have been used for sensor
batch fabrication, thus achieving size miniaturization and low cost.
 Two types of pressure sensors – piezo-resistive and capacitive.

20.  Four sensing resistors connected are
along the edges of a thin silicon
diaphragm.
 An external pressure applied over the
diaphragm introduces a stress on the
sensing resistors, resulting in a
resistance value change corresponding
to the pressure.
 A pressure induced strain deforms the silicon
band structure, thus changing the resistivity of
the material. The piezo-resistive effect is
typically crystal-orientation dependent and is
also affected by doping and temperature. A
practical piezo-resistive pressure sensor can be
implemented by fabricating four sensing
resistors along the edges of a thin silicon
diaphragm, which acts as a mechanical
amplifier to increase the stress and strain at
the sensor site. The four sensing elements are
connected in a bridge configuration with push-
pull signals to increase the sensitivity.
 The measurable pressure range can be from 10^(-3)
to 10^6 Torr.

21.  Capacitive pressure sensors are attractive because they are virtually temperature independent
and consume zero DC power. The devices do not exhibit initial turn-on drift and are stable over
time.
 Furthermore, CMOS microelectronic circuits can be readily interfaced with the sensors to provide
advanced signal conditioning and processing, thus improving overall system performance.
 The diaphragm can be square or circular
with a typical thickness of a few
micrometres and a length or radius of a
few hundred micrometres, respectively.
The vacuum cavity typically has a depth of
a few micrometres. The diaphragm and
substrate form a pressure dependent air
gap variable capacitor.
Cross-sectional schematic of a capacitive pressure sensor.

22. SEM micrograph of polysilicon surface-micromachined
capacitive pressure sensors
Photo of a touch-mode capacitive pressure sensor

23.  Micro-machined inertial sensors, silicon-based MEMS sensors, consist of accelerometers and
gyroscopes and have been successfully commercialized.
 Inertial sensors fabricated by micromachining technology can achieve reduced size, weight,
and cost, all which are critical for consumer applications.
 More importantly, these sensors can be integrated with microelectronic circuits to achieve a
functional micro-system with high performance.
 An accelerometer generally consists of a proof mass suspended by compliant mechanical
suspensions anchored to a fixed frame.
 An external acceleration displaces the support frame relative to the proof mass.
 The displacement can result in an internal stress change in the suspension, which can be
detected by piezo-resistive or capacitance sensors as a measure of the external acceleration.
 Capacitive sensors are attractive for various applications because they exhibit high sensitivity
and low temperature dependence, turn-on drift, power dissipation, and noise.
 Capacitive accelerometers may be divided into two categories: vertical and lateral sensors.

24.  Schematics of
(a) Vertical
(b) Lateral accelerometers by using parallel-plate
sense capacitance
In a vertical device, the proof mass is suspended
above the substrate electrode by a small gap
typically on the order of a micrometer, forming a
parallel-plate sense capacitance. The proof mass
moves in the direction perpendicular to the substrate
(z-axis) upon a vertical input acceleration, thus
changing the gap and the capacitance value. The
lateral accelerometer consists of a number of
movable fingers attached to the proof mass, forming
a sense capacitance with an array of fixed parallel
fingers. The sensor proof mass moves in a plane
parallel to the substrate when subjected to a lateral
input acceleration, thus changing the overlap area of
these fingers and, hence, the capacitance value.

25. Integrated capacitive type, silicon accelerometers
Full scale sensitivity from less than 1 g
to over 20,000 g

26.  Radiation sensors cover ionising radiation as well as visible light, infra-red (IR) and ultraviolet
(UV) radiation. Current ionising radiation sensors for high-energy particles and X-rays include
Geiger-Müller (GM) tubes and scintillators and although they have not been realized using
MEMS, their miniaturization is potentially feasible
1. Photodiodes: A photodiode is a semiconductor device for measuring light intensity based on
the photoconductive effect (increase in conductivity of a semiconductor on exposure to light).
2. Charge-coupled devices: Charge-coupled devices (CCDs) are one of the most common
photodetectors used in handheld video recorders and many other consumer applications. They
consist of a metal gate (electrode) above a dielectric and a semiconductor substrate. This forms
a metal oxide semiconductor (MOS) capacitor, the charge on which arises from photogenerated
carriers.
3. Pyroelectric sensors: Pyroelectric detectors are an example of indirect optical sensors and are
essentially capacitors whose charge can be altered by illumination or temperature changes. By
converting incident light into heat, which is then measured, pyroelectric sensors have a wide
range of applications in surveillance, military, security consumer markets etc. e.g. human
motion detectors. ZnO is the most common in MEMS devices.

27. Scintillation Detector

28. Gas Filled Detector

29. Micro Electro Mechanical Systems
• Highly miniaturized devices or arrays of devices
combining electrical and mechanical components,
such as sensors, valves, actuators or complete
systems.
• Fabricated by using integrated circuit (IC) batch-
processing techniques
Dr. Ramesh K. Guduru - Micro and Nano Manufacturing 29

30. Evolution of Micromachining and MEMS
• The concept of MEMS was first put forward
in 1958 by Jack Kilby with the invention of
Integrated Circuits (ICs) which consist of a
large number of individual components
(transistors, resistors and capacitors)
fabricated side by side on a common
substrate and wired together to perform a
particular circuit function.
• The first effort to miniaturization was put forth
by Richard Feynman in 1959
• In 1969, Westinghouse created the resonant
gate Field-Effect Transistor (FET) based on
new microelectronics fabrication techniques
• In 1970s - Bulk-etched silicon wafers were
used as pressure sensors
• Early experiments on surface-micro machined polysilicon were started in the 1980s. Microelectronics industry
enjoyed a great progress in the 1980s as micromachining became popular.
Dr. Ramesh K. Guduru - Micro and Nano Manufacturing 30

31. • MEMS are characterized by miniaturization, multiplicity and
microelectronics
The reduction in size tends to give the following advantages:
• Lower inertia - A smaller system has a lower inertia of mass
enabling the system to move more quickly.
• Microsystems are less prone to thermal distortion and
vibration.
• It allows for stable, more accurate and precise performance for
applications in the fields of medicine, surgery, satellites,
spacecraft engineering and telecommunication systems.
Dr. Ramesh K. Guduru - Micro and Nano Manufacturing 31

32. Micro and Nano Manufacturing 29
MEMS generally consists of two principal components:
(a) a sensing or actuating element
(b) a signal transduction unit
A sensor  perceives useful information from a
surrounding environment and provides one or more
output variables to a measuring instrument
An actuator  creates a force to manipulate itself,
other mechanical devices or the surrounding
environment to perform some useful functions
Dr. Ramesh K. Guduru -

33. MEMS enabled  The idea of systems-on-a-chip.
MEMS enables  Development of smart products,
augmenting the computational ability of
microelectronics
Microelectronic integrated circuits  Brain of a
system, and MEMS augments  Decision-making
capability
• Sensors gather/sense the information from the
environment through measuring mechanical,
thermal, biological, chemical, optical, and
magnetic phenomena.
• Electronics then process the information derived
from the sensors and through some decision-
making capability direct the actuators to respond
by moving, positioning, regulating, pumping and
filtering, thereby controlling the environment for
getting some desired outcome or purpose.
How MEMS are made?
And their applications
Dr. Ramesh K. Guduru - Micro and Nano Manufacturing 33
Link for the video
https://www.youtube.com/watch?v=CNmk-SeM0ZI
Today’s Class Assignment: Watch the Video as well as
refer to online articles, and make a note on the
applications of MEMS in different fields
MUST WATCH THE VIDEO
FOR MEMS APPLICATIONS

34. • The choice of materials in the manufacture of a microsystem is
determined by microfabrication constraints, and also the intended
application
• As MEMS mainly deals with thin-film materials, the properties of
the thin-film materials should be considered as they may differ
from the properties of the bulk material.
• Typical substrate materials used are silicon (Si), germanium (Ge),
gallium arsenide (GaAs), quartz, glasses, metals, ceramics and
polymers.
• Single-crystal silicon is generally used because it is widely available.
• It is mechanically stable and serves as an ideal lightweight structural material.
• It is dimensionally stable even at elevated temperatures (Up to 1400 C) . It has a low thermal
coefficient of expansion. With virtually no mechanical hysteresis, it is suitable for use in sensors
and actuators.
• Silicon also allows a greater flexibility in the designing and manufacturing process
• Silicon compounds such as silicon dioxide (SiO2), silicon carbide (SiC) and silicon nitride (Si3N4)
are also used
• Polymers which include plastics, adhesives, Plexiglas and Lucite are also used
Dr. Ramesh K. Guduru - Micro and Nano Manufacturing 34

35. • MEMS devices are made in a fashion similar to computer microchips and electronics
components.
• The advantage of this manufacturing process is not simply that small structures can be
achieved but also that thousands or even millions of system elements can be fabricated
simultaneously
• Three distinct microfabrication processes, namely - Surface Micromachining, Bulk
Micromachining and the LIGA process.
Today’s Class Assignment:
What is aspect ratio in
MEMS fabrication?
Dr. Ramesh K. Guduru - Micro and Nano Manufacturing 35

36.  Surface micromachining is a technique for building
electromechanical structures in silicon. Combined
with onboard signal conditioning circuits, complete
electromechanical systems can be economically built
on a single piece of silicon.
 Surface micromachining is a fabrication process used
to develop integrated circuits and sensors of various
kinds. Using surface micromachining techniques
allows applications of up to nearly 100 finely applied
layers of circuit patterns on one chip. In comparison,
only five or six layers are possible using standard
micromachining processes.
Surface micromachining uses the individual
layers of a silicon wafer to create a piece on top of
an existing layer.

37. The two basic processes of surface micromachining (a) the one mask process (b) the
two mask process
https://www.youtube.com/watch?app=desktop&v=nmw65l2HUjw

38. • Step 1: Deposition of sacrificial layer
• Step 2: patterning of the sacrificial layer
• Step 3: deposit structural layer (conformal deposition)
• Step 4: liquid phase removal of sacrificial layer
• Step 5: removal of liquid - drying.
Sacrificial
wet etching drying

39. • Air bridge can be formed using sacrificial etching.

40. • Etch holes are required to reduce the time for removing
sacrificial layer underneath large-area structures.

42. • Used in micro optics component assembly.

43. • Step 1: deposition of sacrificial layer.
• Step 2: deposition of structural layer.
• Step 3: deposition of second sacrificial layer.
• Step 4: etching anchor to the substrate.
• Step 5: deposition of second structural layer.
• Step 6: patterning of second structural layer
• Step 7: Etch away all sacrificial layer to
release the first structural layer.

44. LPCVD Process
• Temperature range 500-800 degrees
• Pressure range 200 - 400 mtorr (1 torr = 1/760 ATM)
• Gas mixture: typically 2-3 gas mixture
• Particle free environment to prevent defects on surface (pin
holes)

46. • Polycrystalline silicon
– Polysilicon is deposited at around 580-620 oC and can withstand more
than 1000 oC temperature. The deposition is conducted by decomposing
silane (SiH4) under high temperature and vacuum (SiH4> Si+2H2).
– Polysilicon is used extensively in IC - transistor gate
• Silicon nitride
– Silicon nitride is nonconducting and has tensile intrinsic stress on top of
silicon substrates. It is deposited at around 800 oC by reacting silane
(SiH4) or dichlorosilane (SiCl2H2) with ammonia (NH3) - SiH4+NH3 ->
SixNy+ H.
• Silicon oxide
– The PSG is knows to reflow under high temperature (e.g. above 900 oC); it
is deposited under relatively low temperature, e.g. 500 oC by reacting
silane with oxygen (SiH4+O2-> SiO2+2H2). PSG can be deposited on top
of Al metallization.
– Silicon oxide is used for sealing IC circuits after processing.
– The etch rate of HF on oxide is a function of doping concentration.

47.  Compatible with IC fabrication processes
– Process parameters for gate poly-silicon are well known
– Only slight alterations needed to control stress for MEMS applications
 Stronger than stainless steel
– fracture strength of poly-Si ~ 2-3 GPa, steel ~ 0.2-1 GPa
 Young’s Modulus ~ 140-190 GPa
 Extremely flexible: maximum strain before fracture ~ 0.5%
 Does not fatigue readily
 Several variations of poly-silicon used for MEMS
– LPCVD poly-silicon deposited undoped, then doped via ion implantation, PSG
source, POCl3, or B-source doping
– In situ-doped LPCVD poly-silicon
– Attempts made to use PECVD silicon, but quality not very good (yet) → etches
too fast in HF, so release is difficult

48. Comb drive micro-engine actuates hinged mirror through gear
transmission

50. Reaction
chamber
RF
plasma
generator
Processing
gases

51. • Electroplating
process
description

52. • XeF2
– liquid phase under room temperature
– 2XeF2+Si => 2 Xe + SiF4
– vapor phase under low pressure
– etches silicon with high speed
– http://www.xactix.com/
• BrF3
– solid phase under regular pressure and room temperature
– vapor phase (sublimation) under low pressure
– BrF3 when reacted with water turns into HF at room temperature.
• Both are isotropic etchants

53. • Photoresist
– etching by plasma etching (limited lateral etch extent)
– or by organic solvents (acetone or alcohol)
• Polyimide
– etching by organic solvents
• Advantage
– extremely low temperature process
– easy to find structural solutions with good selectivity
• Disadvantage
– many structural layers such as LPCVD are not compatible.
– Metal evaporation is also associated with high temperature metal
particles, so it is not completely compatible and caution must be
used.

54. • Selectivity
– etch rate on structural layer/etch rate on sacrificial layer must be high.
• Etch rate
– rapid etching rate on sacrificial layer to reduce etching time
• Deposition temperature
– in certain applications, it is required that the overall processing
temperature be low (e.g. integration with CMOS, integration with
biological materials)
• Intrinsic stress of structural layer
– to remain flat after release, the structural layer must have low stress
• Surface smoothness
– important for optical applications
• Long term stability

56.  As the liquid solution gradually
vaporizes, the trapped liquid
exert surface tension force on
the microstructure, pulling the
device down.
 Surfaces can form permanent
bond by molecule forces when
they are close.

57. • For lithography processes
– Lower depth-of-focus requirement
– Reduced optical reflection effects
– Reduced resist thickness variation over steps
• For etching processes:
– Reduced over-etch time required due to steps
• For deposition processes:
– Improved step coverage for subsequent layer deposition

58.  Produce globally planar wafer surfaces
 Solve the depth-of-focus issues of photolithography by achieving a near-atomic- level
flatness
 Necessary for building dense and multilayer integrated circuits
 Reduce potential mechanical stress

59.  Wafer is polished using a slurry containing
 silica abrasives (10-90 nm particle size)
 etching agents (e.g. dilute HF)

60. Two approaches:
 Bringing change in one or more zones of subsurface
 Using thermal and mechanical means without altering the composition
 Altering the chemical composition
 Developing another layer of suitable material at the surface to achieve the
properties desired for the enhancement of tribological life of the component.

61.  Changing the Structure of Surface and Near-Surface Layers:
 a. Mechanical method: Based on localized plastic deformation and so as to achieve
work hardening of near-surface layers
 i. Burnishing
 ii. Shot peening
 b. Thermal methods: Based on localized heating and controlled cooling to obtain
desired microstructure
 i. Flame and induction hardening
 ii. Laser and electron beam hardening
 iii. Plasma and TIG melting

62.  Changing the Chemical Composition of Surface and Near-Surface Layers
 c. Diffusion-based processes
 i. Carburizing: Introducing carbon in low carbon steel;
 ii. Nitriding: Introducing nitrogen in ferritic steel;
 iii. Cyaniding: Increasing concentration of both carbon and nitrogen in steel;
 iv. Boronizing: Introducing boron in steel;
 v. Vanadizing: Introducing vanadium in steel.
 d. Ion implantation: Introducing nitrogen and other elements and controlled
lattice deformation
 e. Laser alloying: Based on the intermixing of alloying elements in the substrate
using controlled melting of near surface layers

63.  Developing a Surface Layer or
Overlays
 f. Diffusion-based processes
 i. Chemical vapor deposition
 ii. Physical vapor deposition
 g. Melting-based methods
 i. Weld overlays
 ii. Laser cladding
 h. Dipping in hot melt-based methods
 i. Hot dip galvanizing
 ii. Hot dip lead-tin coating
 iii. Hot dip aluminizing
 iv. Hot dip chromizing
 Developing a Surface Layer or
Overlays
 i. Electrolysis-based methods
 i. Electroplating of
 1. Cr and Ni for esthetics;
 2. Cd and Zn for controlling corrosion;
 3. Cu and Ag for improving electrical properties;
 4. Hard chromium for enhancing wear resistance.
 ii. Electroless plating (Ni–P and Ni–B) for
improved corrosion and wear resistance
 j. Mechanical methods
 i. Mechanical plating
 ii. Roll bonding
 iii. Explosive bonding
 iv. Hot isostatic pressing

64.  Comparison of few
important surface
modification
techniques with
respect to the
technology level and
complexity is
schematically shown
in figure:

65.  Different process can be compared using the following parameters:
 1. Capability
 a. To handle the material of low or high melting points;
 b. To modify components up to certain size, area, thickness, and depth;
 c. To apply surface modification under fabrication constraints at site or shop;
 d. To reduce thermal or mechanical or tribological or chemical damage on the surface of
workpiece;
 e. To produce smooth surface, Ra;
 f. To provide control over the surface modification processes.
 2. Initial investment, availability, and expertise needed.

66.  Shot Peening
Induces compressive stress on the surface of a
material to improve fatigue life and resistance to
corrosion and cracking.
 Laser surface melting
Induces melting of the surface of a material followed
by rapid solidification to create a dense and smooth
surface layer with improved wear and corrosion
resistance.
 Ion Implantation
Injects ions into the surface of a material to modify its
mechanical, electrical, and optical properties.
 Plasma Spraying
Sprays fine particles or droplets of a material onto a
surface to create a thick coating with improved wear,
corrosion, and heat resistance.

67.  "Surface modification technology" means applying special treatment to the material surface
which alters its chemical composition or structure to add a new feature to the base material's
characteristics.
 This modification is usually made to solid materials, but it is possible to find examples of the
modification to the surface of specific liquids.
 Surface modification is done via Intentional and Unintentional techniques.

68. None of these process changes the surface chemistry, but they improve properties like wear
and fatigue by changing surface metallurgy. In this section, surface hardening is limited to
localized heat treating processes that produce a hard quenched surface without introducing
additional alloying species.
a) Localized surface hardening (flame, induction, laser, and electron-beam hardening):
Improves wear resistance through the development of a hard martensitic surface.
b) Laser melting: Improves wear resistance through grain refinement and the formation of
fine dispersions of precipitates on the surface.

69. Surface modification that change the surface chemistry of a metal or alloy, but that do not involve intentional buildup
or increase in part dimension, include:
The process includes:
(a) Chemical or electrochemical conversion treatment that produce complex phosphates, chromates/oxides on metal
surface.
(b) Thermo chemical diffusion heat treatment that involves the introduction of interstitial elements like C, N or B
into ferrous alloy surface at elevated temperature.
(c) Pack cementation diffusion treatments that involve the introduction of aluminium(Al), Cr or silicon(Si) into alloy
surface.
(d) Surface modification by ion implantation, which involves introduction of ionized species (virtually any element)
into the substrate using ion beam of high velocity electrons.
(e) Surface modification by combination of laser beam melting and alloying.

70. 1. Heat treatment / Diffusion
2. Ion Bombardment
3. Sputtering
4. Surface coating
5. Hardfacing

71. Hardfacing is one of the versatile techniques that can produce the hard and wear resistant
surface layer of various metals and alloys on metallic substrate.
A. Hardfacing by Arc Welding
B. Hardfacing by Gas Welding
C. Hardfacing by Combination of Arc and Gas
D. Powder Spraying
E. Laser Hardfacing

72. Surface coating methods are classified as under:
A. Thermal Spraying (Metal Spraying)
B. Chemical Vapor Deposition (CVD)
C. Physical Vapor Deposition (PVD)

74. 1. Quench to form surface martensite
2. Or hold in charcoal for ~24hrs to allow carbon to diffuse into the
Hard outer layer
Soft, flexible bulk
• Knife hardening
– Heat to Austenitic temperature

75. PLASMA DEPOSITION
RF Power heats electrons (>100,000 K)
Electron impacts fragment gas molecules, making
them reactive
A + e-  A+ + 2e-
B-B + e-  B∙ + B∙ + e-
Reactive molecules deposit on substrate

76.  Plasma deposition is a way of creating very thin polymer- like layers. A major advantage of
plasma deposition is that it can be used to coat most surfaces and shapes, provided that the
material can tolerant a vacuum.
 In plasma deposition, an RF source is applied to an electrode, generating positive ion and negative
electron pairs.
 The field strength across the system drives these apart.
 The electrons speed up in field, gaining energy and heating up to around 30,000K and as high as
100,000K.
 With this energy the electron can strike other atoms and ionise them, creating another positive
ion and electron pair. This new electron subsequently heats up and the process continues.
 Molecules within the system may be broken open in this manner, creating radicals. These are
very reactive and will react with any surface they collide with, creating a polymeric type deposit.
Plasma deposition is most often used with organic molecules such as acrylic acid.

77. SPUTTERING
 Ions bombard a target (metal)
 Metal atoms etched from target
 Metal atoms accelerated to
substrate
 Metallic coatings can be very thin
Few nanometres

78. ION BOMBARDMENT
 High energy ions impact surface
 Alter surface chemistry
 Alter roughness
Tissue Culture PS

79. SURFACE ANALYSIS
 X-ray Photoelectron Spectroscopy (XPS)
 Atomic Force Microscopy (AFM)
 Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS)
 Scanning Electron Microscopy (SEM)
The term surface analysis describes the methods used to do so. Surface analysis is different
from bulk analysis, as they need to analyse thin layers with unique properties from the bulk
material.

81.  Following are the five very significant surface properties:
 Surface energy
 Chemical composition
 Microstructure
 Hardness
 Surface roughness
 These affect the wear and friction behavior significantly

82.  However, all these properties except the surface roughness are
interdependent and are influenced by thermal and mechanical
history experienced by the surface of substrate during the service.
 A variation in chemical composition generally changes the
microstructure, hardness, and surface energy.
 Surface roughness is determined by the method of manufacturing
used for the generation of the surface which is invariably
characterized in terms of Ra.

83.  A metal may look clean and polished, however
the surface microlayers as shown in figure,
have been formed due to external factors
including machining, temperature and oxide
formation.
The desired properties or characteristics of surface-
engineered components include:
• Improved corrosion resistance through
barrier or sacrificial protection
• Improved oxidation and/or sulfidation
resistance
• Improved wear resistance
• Improved mechanical properties, for example,
enhanced fatigue or toughness
• Improved electronic or electrical properties
• Improved thermal insulation
• Improved aesthetic appearance

84. Three components of surface
textures
Surface asperities of a
nominal smooth surface

85. For point atoms or the vertices of a tiling, the higher-
dimensional structure consists of a periodic array of
objects with a dimension equal to n-m, the difference
between the rank of the Fourier module and the
dimension of the physical space (usually three), and
transverse (i.e. not tangential) to the physical space.
The atomic surface is the (n-m)-dimensional object in
superspace (see figure) corresponding to a point atom in
physical space.

86. • Surface engineering involves modifying the properties of a surface, while maintaining the bulk
properties of the material.
• Modification of near-surface structure, chemistry or property of a substrate in order to achieve superior
performance and/or durability. It is an enabling technology and can impact a wide range of industrial
sectors.
Surface modification
Surface coating
Combining chemistry, physics, and mechanical engineering with
metallurgy and materials science, it contributes to virtually all
engineering disciplines.- It can be done on a given surface by
metallurgical, mechanical, physical, and chemical means, or by
producing a thick layer or a thin coating.- Both metallic and non-
metallic surfaces can be engineered to provide improved property or
performance.

87. (a) Precision required on mating surfaces, such as seals, gaskets, fittings, and tools and dies. For example,
ball bearings and gages require very smooth surfaces, whereas surfaces for gaskets and brake drums can
be quite rough.
(b) Tribological considerations, that is, the effect of surface roughness on friction, wear, and lubrication.
(c) Fatigue and notch sensitivity, because rougher surfaces generally have shorter fatigue lives.
(d) Electrical and thermal contact resistance, because the rougher the surface, the higher the resistance will
be.
(e) Corrosion resistance, because the rougher the surface, the more the possibility that corrosive media may
be entrapped.
(f) Subsequent processing, such as painting and coating, in which a certain degree of roughness can result in
better bonding.
(g) Appearance, because, depending on the application, a rough or smooth surface may be preferred.
(h) Cost considerations, because the finer the finish, the higher is the cost.

88. Surface engineering has significant role to play in our day-to-day lives as it has led to:
 The possibility of producing tools, machine components and whole appliances from the
materials with lower properties, usually cheaper, and giving their surface improved
characteristics.
 Improvement of reliability of work of tools, machine components and appliances and
reduction of failures.
 Reduction of frequency of replacing used tools and machine parts, as well as frequency of
maintenance overhauls.
 Reduction by 15 to 35% of losses due to corrosion.
 Minimization of environmental pollution, primarily due to reduction of energy consumption.
• HARDNESS
• ROUGHNESS/ FRICTION
• WETABILITY
• CHEMICAL STABILITY

89. 89
Fdx= gdA = gLdx
 It is an experimental observation
that liquids tend to draw up into
spherical drops.
 A sphere is the geometric form
which has the smallest surface
area for a given volume.
 Thus it is clear that the surface of
the liquid must have a higher
energy than the bulk.
 This energy is known as the free
surface energy g, with units of Jm-
2 and typical values of 30-100
mJm-2.
 Sometimes the unit is given
equivalently as Nm-1, particularly
when quoted as a surface tension.
 The free surface energy is
equivalent to a line tension acting
in all directions parallel to the
surface.
 We can use a virtual work
argument to show this for a force
F acting on an area dA and
moving through a distance dx:
 Thus g = F/L
 And the surface energy is
equivalent to a line tension per
unit length ie a surface tension.
F
L
dx

90. Surface tension is a property of liquid and has a tendency to contract hence liquid occupy the minimum
surface area and surface of liquid is under tension due to force of attraction.
Due to force of attraction of liquid molecules the free surface of liquid behaves like elastic membrane or
rubber sheet. And a particular kind of tension produces on the surface of liquid.
At the simplest level, we can ascribe the existence of surface tension to the reduction in bonds for
molecules at the liquid surface.
Formally it is the additional free energy per unit area required to remove molecules from the bulk to
create the surface.
Denoted by
i
i
i n
P
T
n
V
T
n
V
S A
G
A
F
A
U
,
,
,
,
,
,








=








=








=
g

91. Following are the examples by which we can understand the
property of surface tension
1. The small insects are easily walking on the surface of
liquid
2. The small drop of water and mercury are in spherical
shape.
3. A painting brush dipped into water and taken out their
fibers comes very close together due to surface tension.
4. A small needle easily floats on the surface of water due
to surface tension

92. 1. Adhesive force:- The intermolecular force of attraction between two different substance is
known as adhesive force.
Ex.:- Force of attraction between water molecule and glass molecule.
2. Cohesive force:- The intermolecular force of attraction between two same substance is known
as adhesive force.
Ex.:- Force of attraction between mercury molecule and glass molecule.
3. Sphere of influence :- It is an imaginary sphere surrounding a molecule is known as sphere of
influence
4. Molecular range:- It is the maximum distance up to which there is a existence of cohesive
force.

93.  Molecule A:- In molecule A, the sphere of influence is totally inside the liquid then the molecule A is attracted
by the side way molecules with equal force of attraction hence the resultant force acting on molecule A is zero.
 Molecule B:- In molecule B, the small portion of sphere of influence lies above the surface of liquid and major
portion inside the liquid which contains large no. of liquid molecules so molecule B is attracted from
downward directions and hence resultant force acts on molecule B is in downward direction.
 Molecule C:- In molecule C, the half portion of sphere of influence lies above the surface having no liquid
molecules and half portion inside the liquid which contains no. of liquid molecules so molecule C is attracted
from downward directions and hence resultant force acts on molecule C is in downward direction.

94. Surface Damage without
exchange of material
Structural Changes
Plastic Deformation
Surface Cracking

95. Surface Damage by gaining material
Material Pick-up
Corrosion

96. Surface Damage by losing material
Wear

97.  Wear is the erosion of material from a solid surface by the
action of another solid, or
 It is a process in which interaction of surface(s) or
bounding face(s) of a solid with the working environment
results in the dimensional loss of the solid, with or without
loss of material
 Wear environment includes loads(types include
unidirectional sliding, reciprocating, rolling, impact),speed,
temperatures, counter-bodies(solid, liquid, gas), types of
contact (single phase or multiphase in which phases
involved can be liquid plus solid particles plus gas bubbles)
WEAR
Abrasive
Adhesive
Corrosion
Erosion

98. 98
a. Adhesive wear
Adhesive wear is also known as scoring, galling, or seizing. It occurs
when two solid surfaces slide over one another under pressure. Surface
projections, or asperities, are plastically deformed and eventually
welded together by the high local pressure. As sliding continues, these
bonds are broken, producing cavities on the surface, projections on the
second surface, and frequently tiny, abrasive particles, all of which
contribute to future wear of surfaces
b. Abrasive wear
When material is removed by contact with hard particles, abrasive
wear occurs. The particles either may be present at the surface of a
second material or may exist as loose particles between two surfaces

99. 99
c. Corrosive wear
Often referred to simply as “corrosion”, corrosive wear is deterioration of useful properties
in a material due to reactions with its environment
d. Surface fatigue
Surface fatigue is a process by which the surface of a material is weakened by cyclic
loading, which is one type of general material fatigue

100.  Corrosion is breaking down! of essential properties in a material due to reactions with its
surroundings. In the most common use of the word, this means a loss of an electron of
metals reacting with water and oxygen
 Weakening of iron due to oxidation of the iron atoms is a well-known example of
electrochemical corrosion. This is commonly known as rust This type of damage usually
affects metallic materials, and typically produces oxide(s) and/or salt(s) of the original metal
100

101. 101
Rust, the most familiar
example of corrosion
-- Most structural alloys corrode merely from exposure to
moisture in the air, but the process can be strongly affected by
exposure to certain substances. Corrosion can be concentrated
locally to form a pit or crack, or it can extend across a wide
area to produce general deterioration

102. 1. Intrinsic chemistry:
The materials most resistant to corrosion are those for which corrosion is
thermodynamically unfavorable. Any corrosion products of gold or platinum tend to
decompose spontaneously into pure metal, which is why these elements can be found
in metallic form on Earth, and is a large part of their intrinsic value
102
GOLD nuggets do not
corrode, even on a
geological time scale.

103. 103
2. Passivation:
Given the right conditions, a thin film of corrosion products can form on a metal's
surface spontaneously, acting as a barrier to further oxidation. When this layer
stops growing at less than a micrometer thick under the conditions that a material
will be used in, the phenomenon is known as passivation
Passivation in air and water is seen in such materials as aluminum, stainless steel,
titanium, and silicon

104. 104
3. Surface treatment ( coating ):
Plating, painting, and the application of enamel are the most common anti-corrosion
treatments. They work by providing a barrier of corrosion-resistant material between
the damaging environment and the (often cheaper, tougher, and/or easier-to-process)
structural material
Example: chromium on steel

105.  Melting is a process that results in the phase change of a substance from a solid
to a liquid. The internal energy of a solid substance is increased (typically by the
application of heat) to a specific temperature (called the melting point) at which it
changes to the liquid phase. An object that has melted completely is molten
 The melting point of a substance is equal to its freezing point
105

106. 106
• Molecular vibrations
When the internal energy of a solid is increased by the application of an
external energy source, the molecular vibrations of the substance increases. As
these vibrations increase, the substance becomes more and more disordered
• Constant temperature
Substances melt at a constant temperature, the melting point. Further
increases in temperature (even with continued application of energy) do not
occur until the substance is molten

107.  Surface fatigue is the failure on the top layer of a body due to repeated loading. It
can be differentiated from other types as it only occurs on the surface. It appears
mainly in the form of microcracks and can propagate to other parts of the body, if
left unchecked. Surface fatigue can have various causes, including:
 Repeated impact
 Repeated shear stresses
 Fretting wear, or wear that is caused by a oscillating contact between two members

108.  Impact is a high force or shock that occurs in a short period of time. When surface fatigue is active
the cracks form like in the case of sliding contact, but now the hard white layer is the main cause.
Material removal by delamination or spalling.
Delamination: It is the process of crack propagation through weak interface of below white layer.
Spalling: It is the process of crack propagation parallel to the flow lines in deformation zone.

109.  In addition to surface pitting, repeated sliding contact may also cause horizontal subsurface
cracks to grow. The surface is deformed plastically, but a compressive stresses restrains crack
growth in the surface layer. Subsurface, where the compressive stress is lower, cracks start to
initiate around discontinuities, such as hard inclusions and voids, or around dislocation pile-
ups.
 The cracks grow horizontally under deformed layer, coalesce and finally lead to detachment of
thin sheets. This kind of wear is also called as delamination wear.

110.  Gears fail due to several mechanisms, most often due to surface pitting of gear teeth fanks. Surface
pitting is in fact the principal mode of failure of mechanical elements that are subjected to rolling
contacts like gears, bearings, shafts, etc., and governs the surface life of a component under applied
load.
Gear pitting

111. 111
Results from crack propagation
 Griffith Crack
where
t = radius of curvature
so = applied stress=F/A
sm = stress at crack tip
o
t
/
t
o
m K
a
s
=









s
=
s
2
1
2
t
Stress Concentration
Flaws: are called stress raiser

112. 112
• Stress amplification is not restricted
to these microscopic defects; it may
occur at macroscopic internal
discontinuities (e.g., voids), at sharp
corners, and at notches in large
structures.
• The effect of a stress raiser is more
significant in brittle than in ductile
materials. For a ductile material,
plastic deformation ensues when the
maximum stress exceeds the yield
strength. This lead to a more uniform
distribution of stress in the vicinity of
the stress raiser. Such yielding and
stress redistribution do not occur to
any appreciable extent around flaws
and discontinuities in brittle
materials; therefore, essentially the
theoretical stress concentration will
result.

113. 113
r/h
sharper fillet radius
increasing
w/h
0 0.5 1.0
1.0
1.5
2.0
2.5
Stress Conc. Factor, K t
s
max
s
o
=
• Avoid sharp corners!
s
r ,
fillet
radius
w
h
o
smax
It is a measure of
the degree to which
an external stress is
amplified at
the tip of a crack.

114. 114
Cracks propagate due to sharpness of crack tip
 A plastic material deforms at the tip, “blunting” the crack.
deformed region
brittle
Energy balance on the crack
 Elastic strain energy-
 energy stored in material as it is elastically deformed
 this energy is released when the crack propagates
 creation of new surfaces requires energy
plastic

115. 115
Crack propagates if applied stress is above critical stress sc ( it
is the stress required for crack propagation in a brittle
materials)
where
 E = modulus of elasticity
 gs = specific surface energy
 a = one half length of internal crack
 Kc = sc/s0
For ductile => replace gs by gs + gp
where gp is plastic deformation energy
2
1
2
/
s
c
a
E







g
=
s
i.e., sm > sc
or Kt > Kc

116. 116

117.  Relationship between critical stress for crack propagation (σc) to crack length (a)
117
- Is fracture toughness, a property that is a measure of a
material’s resistance to brittle fracture when a crack is present.
Y - is a dimensionless parameter or function that depends on both
crack and specimen sizes and geometries, as well as the
manner of load application.( Y = 1 – 1.1)

118. 118
Based on data in Table B5,
Callister 7e.
Composite reinforcement geometry is: f
= fibers; sf = short fibers; w = whiskers;
p = particles. Addition data as noted
(vol. fraction of reinforcement):
1. (55vol%) ASM Handbook, Vol. 21, ASM Int.,
Materials Park, OH (2001) p. 606.
2. (55 vol%) Courtesy J. Cornie, MMC, Inc.,
Waltham, MA.
3. (30 vol%) P.F. Becher et al., Fracture
Mechanics of Ceramics, Vol. 7, Plenum Press
(1986). pp. 61-73.
4. Courtesy CoorsTek, Golden, CO.
5. (30 vol%) S.T. Buljan et al., "Development of
Ceramic Matrix Composites for Application in
Technology for Advanced Engines Program",
ORNL/Sub/85-22011/2, ORNL, 1992.
6. (20vol%) F.D. Gace et al., Ceram. Eng. Sci.
Proc., Vol. 7 (1986) pp. 978-82.
Graphite/
Ceramics/
Semicond
Metals/
Alloys
Composites/
fibers
Polymers
5
K
Ic
(MPa
·
m
0.5
)
1
Mg alloys
Al alloys
Ti alloys
Steels
Si crystal
Glass -soda
Concrete
Si carbide
PC
Glass 6
0.5
0.7
2
4
3
10
20
30
<100>
<111>
Diamond
PVC
PP
Polyester
PS
PET
C-C(|| fibers) 1
0.6
6
7
40
50
60
70
100
Al oxide
Si nitride
C/C( fibers) 1
Al/Al oxide(sf) 2
Al oxid/SiC(w) 3
Al oxid/ZrO 2(p)4
Si nitr/SiC(w) 5
Glass/SiC(w) 6
Y2O3/ZrO 2(p)4
KIC - plane strain
fracture toughness

119. 119
The three modes of crack surface displacement. (a) Mode I,
opening or tensile mode; (b) mode II, sliding mode; and ( c)
mode III, tearing mode.

120. 120
• Crack growth condition:
• Largest, most stressed cracks grow first!
K ≥ Kc = a
Y c 
s
--Result 1: Max. flaw size
dictates design stress.
m
ax
c
design
a
Y
K


s
s
amax
no
fracture
fracture
--Result 2: Design stress
dictates max. flaw size.
2
1








s


design
c
max
Y
K
a
amax
s
no
fracture
fracture

121. 121
Plane strain fracture toughness c
k1
a
Y
K c 
s
=
1
c
k1 Exist when specimen thickness is much greater than the crack dimensions, Kc
becomes independent of thickness; under these conditions a condition of
plane strain exists. By plane strain we mean that when a load operates on a
crack there is no strain component perpendicular to the front and back faces.
The Kc value for this thick-specimen situation is known as the plane strain
fracture toughness KIc
The plane strain fracture toughness KIc is a fundamental material
property that depends on many factors, the most influential of which
are temperature, strain rate, and microstructure. The magnitude of KIc
diminishes with increasing strain rate and decreasing temperature.
increases with reduction in grain size

122. 122
• Two designs to consider...
Design A
--largest flaw is 9 mm
--failure stress = 112 MPa
Design B
--use same material
--largest flaw is 4 mm
--failure stress = ?
• Key point: Y and Kc are the same in both designs.
Answer: MPa
168
)
( B =
sc
• Reducing flaw size pays off!
• Material has Kc = 26 MPa-m0.5
• Use...
max
c
c
a
Y
K

=
s

sc amax
 A
= sc amax
 B
9 mm
112 MPa 4 mm
--Result:

123. The selection of an appropriate material and its subsequent conversion into a useful product with desired
shape and properties can be a rather complex process. Nearly every engineered item goes through a
sequence of activities that includes:
design material selection process selection production evaluation
possible redesign or modification

124. The selection of a specific material for a particular use is a very complex process. However, one can
simplify the choice if the details about:
1) operating parameters,
2) manufacturing processes,
3) functional requirements
4) cost considerations are known.
Material Properties
The expected level of performance from the
material
Material Cost and Availability
1. Material must be priced appropriately (not
cheap but right)
2. Material must be available (better to have
multiple sources)
Processing
Must consider how to make the part, for example:
1. Casting
2. Machining
3. Welding
Environment
1. The effect that the service environment has on the
part
2. The effect the part has on the environment
3. The effect that processing has on the environment