palanivendhan palani vendaN MATERIALS TECHNOLOGY SRM UNIVERSITY

2. What is Materials Technology?
• Metals, Plastics and Ceramics have completely different properties which means
technology involved for production is also different.
• Evolving discipline with new materials leading to new applications.
Raw
Materials
Processing
of materials
Required
shapes &
forms
Specific
Applications

3. Metallic Non-Metallic
Ferrous Non-Ferrous
Steels Cast Iron
Plain Carbon
Alloy
Grey
White
Malleable
Ductile
Alluminium
Copper
Magnesium
Tin
Zinc
Lead
Nickel and
their alloys
Organic Inorganic
Plastics
Wood
Paper
Rubber
Leather
Petroleum
Products
Minerals
Cement
Glass
Ceramics
Graphite
Materials used in automobiles
Material Science

4. Why Mechanical properties
• Materials used in cryogenics where the working temperature is below -157 deg C
• Materials that are used at high temperatures such as blast furnace where the temperature is more
than 1600 deg C
• In the manufacture of railway wheels, dies and punches, where the load delivered may be as high
as 4500 tones.
• In the manufacture of valves and pipes used in chemical industries where the material can undergo
severe corrosion.
• In the design of concrete structures for civil structures
• In the design of space craft where the temperature in the nose region may be as high as 1400 deg C
when it re-enters the earth’s atmosphere.

5. Few Mechanical Properties
• Stress
• Strain
• Elasticity
• Creep
• Strength
• Maelability
• Toughness
• Tensile
• Elongation
• Ductile
• Fracture
• Tension
• Flexural
• Plasticity
• Resiliance
• Yield

6. ELASTIC AND PLASTIC BEHAVIOUR
ELASTICITY
“Elasticity is the physical property
of materials which return to their
original shape after the stress that
caused their deformation is no
longer applied.”(within elastic limit)
PLASTICTY
Is the property of a material where it
undergoes permanent deformation
under the load.

7. • Elastic deformation: Small – Time dependant- Fully recoverable- obeys hookes
law- occurs in metal within elastic limit
• Elastometric deformation: Very Large- Time dependant –Fully recoverable- does
not obeys hookes law- occurs in elastomers.
• Plastic deformation or inelastic deformation: Large – Permanent – Time
independent-obeys hookes law- occurs beyond plastic limits.
• Anelastic deformation: Small-Fully recoverable-time dependant-may or may not
obey hooke’s law-occurs in rubber and plastics and metals due to thermoelastic
phenomenon
• Viscoelastic deformation: Time dependant-partially elastic and partially
permanent-obeys hookes law along with newtons law- occurs in polymers
Types of Deformation

8. ELASTICITY IN METALS
• It is convenient to express the elasticity of the material with the ratio
of stress is to strain, a parameter also termed as young’s modulus.
• The stress and strain relationship is unique for each metal.

9. BRITTLE MATERIALS
• Brittle materials, which includes cast iron, glass, and stone,
are characterized by the fact that rupture occurs without any
noticeable prior change in the rate of elongation.

10. DUCTILE MATERIALS
• They include steel, copper, tungsten etc
• The yield strength or yield point of a material is defined as the stress at which a
material begins to deform plastically. Prior to the yield point the material will
deform elastically and will return to its original shape when the applied stress is
removed. Once the yield point is passed, some fraction of the deformation will be
permanent and non-reversible.
• Ultimate tensile strength is the maximum stress that a material can withstand
while being stretched or pulled before necking.
• Necking is when large amount of strain is applied and there is a prominent
decrease in the cross-sectional area, which provides the name “necking”.

12. POLYMERS
• A polymer is a large molecule (macromolecule) composed of repeating structural
units. These sub-units are typically connected by covalent chemical bonds.
• Examples of polymers are plastic, rubber, proteins etc
• Elastic properties of polymers differ from metals.
• Their elastic moduli are very small when compared to those of metals
• They endure large deformation without rupture and can still return to their original
shape.
• Their elastic moduli is increased with temperature.

13. MECHANISMS OF PLASTIC
DEFORMATION
• This type of deformation is irreversible.
• However, an object in the plastic deformation range will first have undergone elastic
deformation, which is reversible.
• Thermoplastics have large plastic deformation when compared to brittle and ductile materials.
• Plastic deformation is characterized by a strain hardening region and a necking region and
finally, fracture (also called rupture).
• During strain hardening the material becomes stronger through the movement of atomic
dislocations.(dislocations are imperfections in crystal structure which increases as strain
increases)
• There are two types of dislocations: edge and screw.
• The modes of deformation are twinning and slip.
• Necking, in engineering or materials science, is a mode of tensile deformation where relatively
large amounts of strain localize disproportionately in a small region of the material. The
resulting prominent decrease in local cross-sectional area provides the basis for the name
"neck".
• This type of deformation is also irreversible. A break occurs after the material has reached the
end of the elastic, and then plastic, deformation ranges. At this point forces accumulate until
they are sufficient to cause a fracture. All materials will eventually fracture, if sufficient forces
are applied.

14. Mechanism of elastic and plastic deformation

15. • TWINNING
• Common in hcp and bcc
structures
• Limited deformation
but help in plastic
deformation in hcp and
bcc crystals.
• Occurs on specific
twinning planes and
twinning directions
• SLIP
• Dislocations move on a
certain crystallographic
plane: slip plane
• Dislocations move in a
certain crystallographic
direction: slip direction
• The combination of slip
direction and slip plane
is called a slip system.

16. Yield stress for real crystals
• The stress level at which a metal or other material ceases to behave elastically. The
stress divided by the strain is no longer constant. The point at which this occurs is
known as the yield point.
• The initial elastic strain is caused by the simple stretching of bonds. Hooke's Law
applies to this region.
• At the yield point, stage I begins. The crystal will extend considerably at almost
constant stress. This is called easy glide, and is caused by slip on one slip system.
• The geometry of the crystal changes as slip proceeds.
• In this stage of deformation, known as stage II, dislocations are gliding on two slip
systems, and they can interact.
• Consequently, the crystal becomes more difficult to extend. This phenomenon is
called work hardening.
• Stage III corresponds to extension at high stresses, where the applied force
becomes sufficient to overcome the obstacles, so the slope of the graph becomes
progressively less steep. The work hardening saturates.
• Stage III ends with the failure of the crystal.

18. SHEAR STRENGTH FOR PERFECT
CRYSTALS
• It is a term used to describe the strength of a material against structural
failure(fracture), where the material or component fails due to deforming force(
shear force).
• STRENGTH TERMS:-
• Tensile strength or ultimate tensile strength is a limit state of tensile stress that
leads to tensile failure in the manner of ductile failure. or brittle failure.
• Compressive strength is a limit state of compressive stress that leads to failure in
the manner of ductile failure or brittle failure.
• Fatigue strength is a measure of the strength of a material or a component under
cyclic loading, and is usually more difficult to assess than the static strength
measures.
• Impact strength, is the capability of the material to withstand a suddenly applied
load and is expressed in terms of energy.

19. STRENGHTENING MECHANISMS
• Methods have been devised to modify the yield strength, ductility,
and toughness of both crystalline and amorphous materials.
•
• Work hardening (such as beating a red-hot piece of metal on anvil) has
also been used for centuries by blacksmiths to introduce dislocations into
materials, increasing their yield strengths.
•
• Q) What is strengthening?
•
• A) Plastic deformation occurs when large numbers of dislocations move
and multiply so as to result in macroscopic deformation. In other words, it
is the movement of dislocations in the material which allows for
deformation. If we want to enhance a material's mechanical properties
(i.e. increase the yield and tensile strength), we simply need to introduce a
mechanism which prohibits the mobility of these dislocations.

20. WORK HARDENING
• Work hardening is the result of many contributing factors.
• The primary species responsible for work hardening are
dislocations.
• Dislocations interact with each other by generating stress
fields in the material.
• As a material is plastically deformed, dislocations move
extensively throughout the crystal, and in addition
the dislocation density increases.
• The effect of this is to increase the number
of entanglements - these are points where dislocations
interact in such a way that their further motion is hindered.

21. SOLID SOLUTIONING
• Metals usually form homogenous liquid
solutions in their liquid state.
• Even after to solid crystalline state, the metals
retain their homogeneity and consequently
their solubility, this is called solid solution.
• There are two types of solid solution:-
1) Substitutional( (a)disordered and (b)ordered)
2) Interstitial

22. SUBSTITUTIONAL SOLID
SOLUTION
• In this there is a direct substitution
of one type of atom for the another
so that the solute atoms (Cu) enter
the crystals to take the position
normally occupied by solvent
atoms.(Ni)
• In disordered substitutional
solution the atoms do not occupy
any paticular position and are
disordered.
• In ordered solution ,the alloy is in
disordered condition and if it is
cooled slowly, it undergoes
rearrangment of atoms due to
diffusion that takes place due to
cooling.
INTERSTITIAL SOLID
SOLUTION
• It is formed when solute
atoms are very small as
compared to solvent atoms,
they are unable to
substitute solvent
atoms(because of large
difference in diameters) and
can only fit into the
interstices or spaces in the
crystal lattice of the solvent
atom.

23. Grain boundary strengthening
• Is a method of strengthening materials by changing
their average crystallite (grain) size.
• It is based on the observation that grain boundaries
impede dislocation movement and that the number
of dislocations within a grain have an effect on how
easily dislocations can traverse grain boundaries and
travel from grain to grain.
• So, by changing grain size one can influence dislocation
movement and yield strength.
• For example ,heat treatment after plastic For example
,heat treatment after plastic deformation and changing
the rate of solidification are ways to alter grain
size.[deformation and changing the rate of
solidification are ways to alter grain size.

24. GRAIN BOUNDARY STRENGTHENING

25. DISPERSION HARDENING
• Dispersion hardening is a mean of strengthening a metal by
creating a fine dispersion of insoluble particles within the
metal.
• So metals containing finely dispersed particles are much
stronger than the pure metal matrix.
• This effect depends on the size, shape, concentration and
physical characteristics of particles.
• Dispersion hardened materials can be produced with the
help of powder metallurgy- a process in which powder(of
materials) of required shape, size and distribution are
mixed in desired proportions and then compacted and
sintered at the appropriate temperature.

26. PARTICULATE STRENGTHENED
SYSTEMS
• The difference between particulate and dispersion strengthened
systems are in the size of dispersed particles and their volumetric
concentration.
• In dispersion strengthening the particle size are small as compared
to particulate strengthened systems
• Because of their size the particle can not interfere with dislocations
and exhibits a strengthening effect by hydrostatically restraining the
movement of the matrix close to it.
• Particulate composites sre made mainly by powder metallurgy
techniques that may involve solid or liquid state sintering(atomic
diffusions preferably at high temperatures) or even impregnation by
molten metals
• Examples are Tungsten-nickel-iron system obtained as a liquid –
sintered composite.

27. SUPERPLASTICITY
• In materials science, superplasticity is a state in
which solid crystalline material is deformed well beyond its
usual breaking point, usually over about 200% during
tensile deformation.
• Such a process happens at a very high temperature.
• Examples of superplastic materials are some fine-grained
metals and ceramics.
• Other non-crystalline materials (amorphous) such as silica
glass ("molten glass") and polymers also deform similarly,
but are not called superplastic, because they are not
crystalline
• Superplastically deformed material gets thinner in a very
uniform manner, rather than forming a "neck" (a local
narrowing) which leads to fracture.

28. SUPERPLASTICITY OF NANOCRYSTALLINE COPPER AT
ROOM TEMPERATURE

29. DEFORMATION OF NON-CRYSTALLINE
MATERIALS
• In non-crystalline materials, permanent deformation is
often related to localized slip and/or viscous flow (low
stress or high temperature)
• Viscous flow is due to permanent displacement of
atoms in different locations within the material.
• Glass transition temperature is an important factor to
the deformation in non-crystalline material.
• The glass-liquid transition (or glass transition for
short) is the reversible transition
in amorphous materials (or in amorphous regions
within semicrystalline materials) from a hard and
relatively brittle state into a molten or rubber-like
state.