Engineering Materials are classified as metals , non metals. metals are further classified as ferrous and non ferrous alloys. Nonmetals are classified as ceramics and plastics. Classification of advanced materials like composites are also discussed

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
oPlastics – moldable into many shape and have sufficient
structural rigidity. Are one of the most commonly used class
of materials.
oAre used in clothing, housing, automobiles, aircraft,
packaging, electronics, signs, recreation items, and medical
implants.
oNatural 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

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

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,