Engineering materials for students lecture

1. ENGINEERING
MATERIALS
By
Ch.V.Sushma
Assistant Professor
Mechanical Engineering Department
Chaitanya Bharathi Institute of Technology
Hyderabad

2. CLASSIFICATION OF ENGINEERING
MATERIALS

3. METALS AND NON-FERROUS METALS
 Common engineering materials are normally classified as metals
and nonmetals.
 Metals may conveniently be divided into ferrous and non-ferrous
metals. Important ferrous metals for the present purpose are:
(i) cast iron
(ii) wrought iron
(iii) steel.
 Some of the important non-ferrous metals used in engineering
design are:
(a)Light metal group such as aluminum and its alloys,
magnesium and manganese alloys.
(b) Copper based alloys .
(c) White metal group such as nickel, silver, white
bearing metals.

4. FERROUS MATERIALS
Cast iron-
It is an alloy of iron, carbon and silicon and it is hard and
brittle. Carbon content may be within 1.7% to 3% and
carbon may be present as free carbon (graphite) or iron
carbide Fe3C.
In general the types of cast iron are
(a) Grey cast iron
(b) White cast iron
(c) Malleable cast iron
(d) Spheroidal or nodular cast iron
(e) Austenitic cast iron
(f) Abrasion resistant cast iron.

5. GREY CAST IRON
Grey cast iron Carbon content is 3 to 3.5%.
Carbon here is mainly in the form of graphite. This
type of cast iron is inexpensive and has high
compressive strength. It has low tensile strength
and low ductility. Graphite is an excellent solid
lubricant and this makes it easily machinable but
brittle. Some examples of this type of cast iron are
FG20, FG35 or FG35Si15. The numbers indicate
ultimate tensile strength in MPa and 15 indicates
0.15% silicon.

6. GREY CAST IRON
Applications:
Due to lubricating action it
is very suitable for parts
where sliding action is
desired. They are
machine tool bodies,
automotive cylinder
blocks, heads, housings,
fly-wheels, pipes and pipe
fittings and agricultural
implements.

7. AUSTENITIC CAST IRON
Depending on the form of graphite present this cast
iron can be classified broadly under two headings:
Austenitic flake graphite iron, Austenitic spheroidal or
nodular graphite iron .These are alloy cast irons and
they contain small percentages of silicon,
manganese, sulphur, phosphorus etc. They may be
produced by adding alloying elements viz. nickel,
chromium, molybdenum, copper and manganese in
sufficient quantities. These elements give more
strength and improved properties. They are used for
making automobile parts such as cylinders, pistons,
piston rings, brake drums etc.

8. WHITE CAST IRON
White cast iron- Carbon content is 1.75 to
2.3%.In these cast irons carbon is present
in the form of iron carbide (Fe3C) which is
hard and brittle. White cast iron has high
tensile strength and low compressive
strength. The presence of iron carbide
increases hardness and makes it difficult to
machine. Consequently these cast irons
are abrasion resistant.

9. WHITE CAST IRON
Applications:
Due to wear resisting
characteristics it is used
for car wheels, rolls for
crushing grains and jaw
crusher plates.

10. ABRASION RESISTANT CAST IRON
These are alloy cast iron and the alloying
elements render abrasion resistance. A
typical designation is ABR33 Ni4 Cr2 which
indicates a tensile strength in kg/mm2 with
4% nickel and 2% chromium.

11. MALLEABLE CAST IRON
Malleable cast iron- These are white cast irons
rendered malleable by annealing. These are
tougher than grey cast iron and they can be twisted
or bent without fracture. They have excellent
machining properties and are inexpensive.
Depending on the method of processing they may
be designated as black heart BM32, BM30 or white
heart WM42, WM35 etc.

12. MALLEABLE CAST IRON
Applications:
Malleable cast iron is
used for making parts
where forging is
expensive such as hubs
for wagon wheels, brake
supports.

13. SPHEROIDAL OR NODULAR GRAPHITE
CAST IRON
In these cast irons graphite is present in the form of
spheres or nodules. This type of cast iron is formed
by adding small amounts of magnesium (0.1 to 0.8%)
to the molten grey iron. The addition of magnesium
causes the graphite to take form of nodules or
spheroids instead of normal angular flakes. They
have high tensile strength and good elongation
properties. They are designated as, for example,
SG50/7, SG80/2 etc where the first number gives the
tensile strength in MPa and the second number
indicates percentage elongation.

14. SPHEROIDAL OR NODULAR GRAPHITE
CAST IRON
Applications:
Nodular cast iron is
generally used for casting
requires shock and impact
resistance along with
good machinability, such
as hydraulic cylinders,
cylinder heads rolls for
rolling mills and
centrifugally cast
products.

15. WROUGHT IRON
 This is a very pure iron where the iron content is
of the order of 99.5%. It is produced by re-
melting pig iron and some small amount of
silicon, sulphur, or phosphorus may be present.
It is tough, malleable and ductile and can easily
be forged or welded. It cannot however take
sudden shock.
 Applications- Chains, crane hooks, railway
couplings and such other components may be
made of this iron.

16. STEEL
This is by far the most important engineering
material and there is an enormous variety of steel
to meet the wide variety of engineering
requirements. Steel is basically an alloy of iron and
carbon in which the carbon content can be less
than 1.7% and carbon is present in the form of iron
carbide to impart hardness and strength. Two main
categories of steel are
(a) Plain carbon steel
(b) Alloy steel.

17. PLAIN CARBON STEEL
The properties of plain carbon steel depend mainly on
the carbon percentages and other alloying elements
are not usually present in more than 0.5 to 1% such
as 0.5% Si or 1% Mn etc. There is a large variety of
plane carbon steel and they are designated as C01,
C14, C45 and C70 and so on where the number
indicates the carbon percentage.
Following categorization of these steels is sometimes
made for convenience:
 Dead mild steel- up to 0.15% C
 Low carbon steel or mild steel- 0.15 to 0.46% C
 Medium carbon steel- 0.45 to 0.8% C.
 High carbon steel- 0.8 to 1.5% C

18. LOW CARBON STEEL-(MILD STEELS (OR)
SOFT STEELS)-
No alloying element other than carbon is present in low carbon steel.
It has carbon content of 0.15% to 0.45%. However there may small
magnitude of P, S, Si and Mn. They are present as impurities as it is
difficult to remove them in the process of smelting. Because of low
carbon percentage it cannot undergo heat treatment process. Its
hardness cannot be increased by conventional heat treatment
method. The hardness number is about 150BHN. It has lower tensile
strength and malleable.
Applications-
Screws, bolts, nuts, washers, wire fences, automobile body sheet,
plates, wires, building bars, grills, beams, angles, channels etc.

19. MEDIUM CARBON STEEL-(MACHINERY STEELS)
The carbon content of medium carbon steel is 0.45% to
0.8%.Medium carbon steels has higher tensile strength and
hardness than low carbon steels. The hardness number is about
300BHN. Medium carbon steels responds slightly to heat
treatment process and hence its hardness can be further
increased if required for a particular application. They also have
better machining qualities. Generally they are hot worked.
Applications-
Hooks, wire ropes, shafts, connecting rods, spindles, rail axles,
gears, turbine bucket wheels, steering arms and other machine
components which require medium strength.

20. HIGH CARBON STEEL
It has carbon content of 0.8% to 1.7%.High carbon
steels has higher tensile strength and hardness
than medium carbon steels. The hardness number
is about 500BHN. High carbon steels responds
readily to heat treatment process and hence its
hardness can be further increased to desired
values. They have good wear resistance. Generally
they are hot worked.
Applications-
They are used for making hand tools such as
wrenches, chisels, punches and rail wheels, files,
cutting tools like drills, wood working tools and rails,
rods for reinforced concrete, forging dies, knives,
drawing dies, saws etc.

21. ALLOY STEEL
These are steels in which elements other than carbon are
added in sufficient quantities to impart desired properties,
such as wear resistance, corrosion resistance, electric or
magnetic properties.
Chief alloying elements added are usually
• Nickel for strength and toughness
• Chromium for hardness and strength
• tungsten for hardness at elevated temperature
• vanadium for tensile strength
• manganese for high strength in hot rolled and heat treated
condition
• silicon for high elastic limit
• cobalt for hardness
• molybdenum for extra tensile strength

22. Stainless steel
is one such alloy steel that gives good corrosion resistance.
One important type of stainless steel is often described as
18/8 steel where chromium and nickel percentages are
18 and 8 respectively. A typical designation of a stainless
steel is 15Si2Mn2Cr18Ni8 where carbon percentage is
0.15.
High speed steel:
This steel contains 18% tungsten, 4% chromium and 1%
vanadium. It is considered as one of best of all purpose tool
steels. It is used widely for drills, lathe, planer and shaper
tools, milling cutters, reamers, broaches, threading dies,
punches etc.

23. Non-ferrous metals- Metals containing elements other
than iron as their chief constituents are usually referred to
as non-ferrous metals. There is a wide variety of non-
metals in practice.
Aluminum- This is the white metal produced from
Alumina. In its pure state it is weak and soft but addition
of small amounts of Cu, Mn, Si and Magnesium makes it
hard and strong. It is also corrosion resistant, low weight
and non-toxic.

24. Duralumin- This is an alloy of 4% Cu, 0.5% Mn, 0.5% Mg
and aluminum. It is widely used in automobile and aircraft
components.
Y-alloy- This is an alloy of 4% Cu, 1.5% Mn, 2% Ni, 6%
Si, Mg, Fe and the rest is Al. It gives large strength at high
temperature. It is used for aircraft engine parts such as
cylinder heads, piston etc.
Magnalium- This is an aluminum alloy with 2 to 10 %
magnesium. It also contains 1.75% Cu. Due to its light
weight and good strength it is used for aircraft and
automobile components.

25. Copper alloys
Copper- is one of the most widely used non-ferrous metals in
industry. It is soft, malleable and ductile and is a good
conductor of heat and electricity.
Brass (Cu-Zn alloy) - It is fundamentally a binary alloy with
Zn up to 50% . As Zn percentage increases, ductility increases
up to ~37% of Zn beyond which the ductility falls. Small
amount of other elements viz. lead or tin imparts other
properties to brass. Lead gives good machining quality
ductility Zn (%) 37 and tin imparts strength. Brass is highly
corrosion resistant, easily machinable and therefore a good
bearing material

26. Bronze (Cu-Sn alloy)-This is mainly a copper-tin alloy
where tin percentage may vary between 5 to 25. It
provides hardness but tin content also oxidizes resulting
in brittleness. Deoxidizers such as Zn may be added.
Gun metal- is one such alloy where 2% Zn is added as
deoxidizing agent and typical compositions are 88% Cu,
10% Sn, 2% Zn. This is suitable for working in cold
state. It was originally made for casting guns but used
now for boiler fittings, bushes, glands and other such
uses.

27. Non-metals- Non-metallic materials are also used in engineering
practice due to principally their low cost, flexibility and resistance to
heat and electricity. Though there are many suitable non-metals, the
following are important few from design point of view:
Timber- This is a relatively low cost material and a bad conductor of
heat and electricity. It has also good elastic and frictional properties
and is widely used in foundry patterns and as water lubricated
bearings.
Leather- This is widely used in engineering for its flexibility and
wear resistance. It is widely used for belt drives, washers and such
other applications.
Rubber- It has high bulk modulus and is used for drive elements,
sealing, vibration isolation and similar applications. Plastics are
synthetic materials which can be moulded into desired shapes
under pressure with or without application of heat. These are now
extensively used in various industrial applications for their corrosion
resistance, dimensional stability and relatively low cost.

28. Thermosetting plastics- Thermosetting plastics are formed under
heat and pressure. It initially softens and with increasing heat and
pressure, polymerization takes place. This results in hardening of the
material. These plastics cannot be deformed or remolded again
under heat and pressure. Some examples of thermosetting plastics
are phenol formaldehyde (Bakelite), phenol-furfural (Durite), epoxy
resins, phenolic resins etc.
Thermoplastics- Thermoplastics do not become hard with the
application of heat and pressure and no chemical change takes
place. They remain soft at elevated temperatures until they are
hardened by cooling. These can be re-melted and remolded by
application of heat and pressure. Some examples of thermoplastics
are cellulose nitrate (celluloid), polythene, polyvinyl acetate, polyvinyl
chloride ( PVC) etc.

29. POLYMERS
Polymers – Chain of H-C molecules. Each repeat unit of H-C is
a monomer e.g. ethylene (C2H4), Polyethylene – (–CH2 –
CH2)n
Polymers:
Thermo plasts – Soften when heated and harden on cooling –
totally reversible.
Thermosets – Do not soften on heating
o Plastics – moldable into many shape and have sufficient
structural rigidity. Are one of the most commonly used class
of materials.
o Are used in clothing, housing, automobiles, aircraft,
packaging, electronics, signs, recreation items, and medical
implants.
o Natural plastics – hellac, rubber, asphalt, and cellulose.

30. APPLICATIONS OF SOME COMMON THERMOPLASTICS
Material Characteristics Applications
Polyethylene Chemically resistant, tough, low friction
coefficient, low strength
Flexible bottles, toys, battery
parts, ice trays, film wrapping
materials
Polyamide (Nylon) Good strength and toughness,
abrasion resistant, liquid absorber, low
friction coeff.
Bearings, gears, cams,
bushings and jacketing for
wires and cables
Fluorocarbon (Teflon) Chemically inert, excellent electrical
properties, relatively weak
Anticorrosive seals, chemical
pipes and valves, bearings,
anti-adhesive coatings, high
temp electronic parts
Polyester (PET) Tough plastic film, excellent fatigue and
tear strength, corrosion resistant
Recording tapes, clothing,
automotive tyre cords,
beverage containers
Vinyl Low-cost general purpose material,
rigid, can be made flexible
Floor coverings, pipe, electric al
wire insulation, garden hose,
phonograph records
Polystyrene Excellent electrical prop and optical
clarity, good thermal and dimensional
stability
Wall tile, battery cases, toys,
lighting panels, housing
appliances

31. APPLICATIONS OF SOME COMMON THERMOSETS
Material Characteristics Applications
Epoxy (Araldite) Excellent mechanical properties and
corrosion resistance, good electrical
prop., good adhesion and dimensional
stability
Electrical moldings, sinks,
adhesives, protective
coatings, fiber reinforced
plastic (FRP), laminates
Phenolic
(Bakelite)
Excellent thermal stability (>150 C),
inexpensive, can be compounded with
many resins
Motor housings, telephones,
auto distributors, electrical
fixtures
Polyester
(Aropol)
Excellent electrical properties, low cost,
can formulated for room or high
temperature, often fiber reinforced
Helmets, fiberglass boats,
auto body components, chair
fans

32. CERAMICS
Ceramics Materials
• Refractory Materials
• Advanced Ceramics
• Abrasives
• Glass Ceramics

33. REFRACTORY MATERIALS
 Zirconia - extremely high temperatures.
 Sic and Carbon – also used in some very severe
temperature conditions, but cannot be used in oxygen
environment, as they will oxidize and burn.

34. ABRASIVE CERAMICS
o Abrasives are used in cutting and grinding tools.
o Diamonds - natural and synthetic, are used as
abrasives, though relatively expensive. Industrial
diamonds are hard and thermally conductive.
Diamonds unsuitable as gemstone are used as
industrial diamond
o Common abrasives – SiC, WC, Al2O3 (corundum)
and silica sand.
o Either bonded to a grinding wheel or made into a
powder and used with a cloth or paper.

35. ADVANCED CERAMICS
 Automobile Engine parts Advantages:
Operate at high temperatures – high efficiencies; Low
frictional losses; Operate without a cooling system; Lower
weights than current engines Disadvantages: Ceramic
materials are brittle; Difficult to remove internal voids (that
weaken structures);
Ceramic parts are difficult to form and machine Potential
materials: Si 3 N4 (engine valves, ball bearings), SiC
(MESFETS), & ZrO2 (sensors), Possible engine parts:
engine block & piston coatings

36. REFRACTORY MATERIALS
 Refractory - retains its strength at high temperatures > 500°C.
 Must be chemically and physically stable at high
temperatures. Need to be resistant to thermal shock, should
be chemically inert, and have specific ranges of thermal
conductivity and thermal expansion.
 Are used in linings for furnaces, kilns, incinerators, crucibles
and reactors.
 Aluminum oxide (alumina), silicon oxide (silica), calcium oxide
(lime) magnesium oxide (magnesia) and fireclays are used to
manufacture refractory materials.

37. COMPOSITES
A materials system composed of two or more physically
distinct phases whose combination produces aggregate
properties that are different from those of its
constituents
 Examples:
 Cemented carbides (WC with Co binder)
 Plastic molding compounds containing fillers
 Rubber mixed with carbon black
 Wood (a natural composite as distinguished from a
synthesized composite)

38. WHY COMPOSITES ARE IMPORTANT
 Composites can be very strong and stiff, yet very
light in weight, so ratios of strength-to-weight and
stiffness-to-weight are several times greater than
steel or aluminum
 Fatigue properties are generally better than for
common engineering metals
 Toughness is often greater too
 Composites can be designed that do not corrode
like steel
 Possible to achieve combinations of properties not
attainable with metals, ceramics, or polymers alone

39. DISADVANTAGES AND LIMITATIONS OF COMPOSITE
MATERIALS
 Properties of many important composites are
anisotropic - the properties differ depending on the
direction in which they are measured – this may be an
advantage or a disadvantage
 Many of the polymer-based composites are subject to
attack by chemicals or solvents, just as the polymers
themselves are susceptible to attack
 Composite materials are generally expensive
 Manufacturing methods for shaping composite materials
are often slow and costly

40. ONE POSSIBLE CLASSIFICATION OF COMPOSITE
MATERIALS
 Traditional composites – composite materials that
occur in nature or have been produced by
civilizations for many years
 Examples: wood, concrete, asphalt
 Synthetic composites - modern material systems
normally associated with the manufacturing
industries, in which the components are first
produced separately and then combined in a
controlled way to achieve the desired structure,
properties, and part geometry

41. CLASSIFICATION

42. DISPERSION-STRENGTHENED COMPOSITES
In dispersion-strengthened composites, particles are
comparatively smaller, and are of 0.01-0.1μm in size.
Here the strengthening occurs at atomic/molecular
level i.e. mechanism of strengthening is similar to that
for precipitation hardening in metals where matrix
bears the major portion of an applied load, while
dispersoids hinder/impede the motion of dislocations.
Examples: thoria (ThO2) dispersed Ni-alloys (TD Ni-
alloys) with high-temperature strength; SAP (sintered
aluminium powder) – where aluminium matrix is
dispersed with extremely small flakes of alumina
(Al2O3).

43. PARTICULATE COMPOSITES
Particulate composites are other class of particle-reinforced
composites. These contain large amounts of comparatively
coarse particles. These composites are designed to produce
unusual combinations of properties rather than to improve
the strength. Mechanical properties, such as elastic modulus,
of particulate composites achievable are in the range defined
by rule of mixtures.
Particulate composites are used with all three material types
– metals, polymers and ceramics. Cermets contain hard
ceramic particles dispersed in a metallic matrix. Eg.: tungsten
carbide (WC) or titanium carbide (TiC) embedded cobalt or
nickel used to make cutting tools. Polymers are frequently
reinforced with various particulate materials such as carbon
black. When added to vulcanized rubber, carbon black
enhances toughness and abrasion resistance of the rubber.

44. PARTICULATE COMPOSITES
Particulate composites are used with all three material types –
metals, polymers and ceramics. Cermets contain hard ceramic
particles dispersed in a metallic matrix. Eg.: tungsten carbide (WC)
or titanium carbide (TiC) embedded cobalt or nickel used to make
cutting tools. Polymers are frequently reinforced with various
particulate materials such as carbon black. When added to
vulcanized rubber, carbon black enhances toughness and abrasion
resistance of the rubber. Aluminium alloy castings containing
dispersed SiC particles are widely used for automotive applications
including pistons and brake applications. Concrete is most
commonly used particulate composite. It consists of cement as
binding medium and finely dispersed particulates of gravel in
addition to fine aggregate (sand) and water. It is also known as
Portland cement concrete. Its strength can be increased by
additional reinforcement such as steel rods/mesh.

45. FIBER-REINFORCED COMPOSITES
Most fiber-reinforced composites provide improved strength
and other mechanical properties and strength-to-weight ratio
by incorporating strong, stiff but brittle fibers into a softer,
more ductile matrix. The matrix material acts as a medium to
transfer the load to the fibers, which carry most off the applied
load. The matrix also provides protection to fibers from
external loads and atmosphere. These composites are
classified as either continuous or discontinuous. Generally,
the highest strength and stiffness are obtained with
continuous reinforcement.

46. FIBER-REINFORCED COMPOSITES
Discontinuous fibers are used only when
manufacturing economics dictate the use of a
process where the fibers must be in this form. The
mechanical properties of fiber-reinforced composites
depend not only on the properties of the fiber but also
on the degree of which an applied load is transmitted
to the fibers by the matrix phase. Length of fibers,
their orientation and volume fraction in addition to
direction of external load application affects the
mechanical properties of these composites.

47. Effect of fiber orientation and concentration: with
respect to orientation, two extremes possibilities are –
parallel alignment and random alignment. Continuous
fibers are normally aligned, whereas discontinuous
fibers are randomly or partially orientated. Two
instants of loading are: longitudinal loading and
transverse loading.

48. STRUCTURAL COMPOSITES
These are special class of composites, usually consists of
both homogeneous and composite materials. Properties of
these composites depend not only on the properties of the
constituents but also on geometrical design of various
structural elements.
Two classes of these composites widely used are: laminar
composites and sandwich structures.

49. LAMINAR COMPOSITES
Laminar composites: there are composed of two-
dimensional sheets/layers that have a preferred
strength direction. These layers are stacked and
cemented together according to the requirement.
Materials used in their fabrication include: metal
sheets, cotton, paper, woven glass fibers embedded
in plastic matrix, etc. Examples: thin coatings, thicker
protective coatings, claddings, bimetallics, laminates.
Many laminar composites are designed to increase
corrosion resistance while retaining low cost, high
strength or light weight.

50. SANDWICH STRUCTURES
these consist of thin layers of a facing material joined to a
light weight filler material. Neither the filler material nor the
facing material is strong or rigid, but the composite
possesses both properties. Example: corrugated cardboard.
The faces bear most of the in-plane loading and also any
transverse bending stresses. Typical face materials include
Al-alloys, fiber-reinforced plastics, titanium, steel and
plywood. The core serves two functions – it separates the
faces and resists deformations perpendicular to the face
plane; provides a certain degree of shear rigidity along
planes that are perpendicular to the faces. Typical materials
for core are: foamed polymers, synthetic rubbers, inorganic
cements, balsa wood. Sandwich structures are found in
many applications like roofs, floors, walls of buildings, and in
aircraft for wings, fuselage and tailplane skins.