##
**MATERIAL SCIENCE **

Material science:-A study of relationship
between structure and properties of engineering material Microstructure:-microstructure is
defined as the internal structure details of a material, which can be observed
at high magnification under a microscope Microstructure include, 1)
Grain and grain boundaries 2) phase and phase Boundary 3) grain
orientation luster Microscope us observed at magnification more then or
equal to 100x Metallic sample are opaque - metallurgical micro-structure
atom Transparent sample :- pathological microstructure examine (blood
and urine sample ) To change microstructure :- manufacturing
process Properties are depend of phase change :- microstructure change Macrostructure :-It is defined as the
external geometrical characteristics of an object which can observed by naked
eye or under the microscope at lower magnification of the order of less than
100x Only to achieved Macro structure improvement welding , forming ,
machine.

Engineering material :-Crystal structure of unknown material are determine by
x- ray diffraction techniques based on x- ray diffraction studies
crystalline material are classified into 7 crystal structure Crystal system
denotes the basic shape of unit cell whereas Brauias lattice denotes atomic
arrangement within a unit cell Heat treatment is to change the crystal
structure General atomic arrangement Simple, Body centered, Faced
centered, End centred, Crystal
structure :- It denotes the combination of crystal system and
Bravia us lattice. It cannot see by microscope, It can determine by
mathematically Important
definition 1) Unit cell:- It is defined as the smallest representative
group of atoms which when repeated in all the crystallographic direction for
infinite the number of times result in the development of a crystal
lattice 2) space lattice :- It
is defined as the three dimensional network of points in space. It is
also called as a point lattice 3)
premative cell: - It is a simple cubic unit cell having atoms only
at its corners 4) lattice parameter:
- It is defined as the distance between the centred of nibhouring
corner atoms.

Crystal structure characteristics
:-Ex. W , Cr , V , Mo , Ta , Fe (except
910-1400 degree Celsius ) BBC elements are generally hard and brittle (
Tool steel ) FCC AB
= Face diagonal of unit cell Ex. AL, Cu , Ni , Au , Ag , Pt , Fe (
in 910 - 1400 degree Celsius ) FCC elements are strong and
ductile Strength - ductility increase and area under 6 and E diagram
increase Stocking sequence
:- Stocking sequence is defined as the sequence of arrangements of
atomic one above the other in under to result in stability to a crystalline
structure Hexagonal closed packed HCF :- ( Hexagonal prism ) HCP elements are relatively
less ductile compare to FCC elements For a ideal HCP structure like magnesium,
volume estimation = c / a = 1.633 Ex. Ti , Mg , Zn, Zr, Cd , Be ,
Co HCP elements are best suited as solid lubricant because of less
bonding force between two atoms. Avg.
No. Of stems: - Avg no of atoms is defined as the
number of atoms which originally belong to a particular unit cell Where, Ne
= No. Of corner atoms Nf= no. Of face Centre atoms Ni = No of
interior atoms Co- ordination Number:
- Co-ordination number is defined as the number of nearest and equidistance,
atoms surrounding an atom under consideration

To Find coordination no. Of
FCC :- Atomic packing Factor :- ( maximum atomic p F increase Density increase
) It is defined as the ratio of volume occupied by the Avg no
of atoms to the volume of unit cell Allotropy :- It is defined as the tendency of an element to
exist in different crystalline structure at different temperature and pressure
Thermodynamically reversible form of Allotropic transformation are called as
polytropic transformation / polymorphic transformation Miller Indices of planes :- Rationalised
reciprocal of frictional intercepts taken along the three crystallographic
direction and written inside parenthesis, without a separating comma
between Indicated by (hkl) Always written as smallest integers

Characteristics of Miller Indices
of planes:- 1) when a plane is parallel
to axis it's Miller index on that axis is zero 2) Two parallel planes will have
quantitatively same Millar Indices 3) Two planes h, k, l, and h2, k2, l2, will
be perpendicular if h1 h2 + k1 k2 + L1 L2 =0 4) The angle '@' between two
intersection plane ( h1 k1 L1 ) and ( h2 k2 l2 ) is given by 5)
planes having low Indices are for away from origin than those having high
Indices Interplaner distance :-Interplaner
distance is defined as the distance between two parallel planes , one of
which is passing through a origin It is the same as distance of the given plane
from the origin Millar Indices of
direction :- Rationalised component of given direction vector and
written inside square brackets without a zeperation comma between then Indicated
by ( u v w ) Always expressed as smallest integers

Characteristics of Miller Indices
of direction :-1) when direction is
perpendicular to an axis it's Miller index on that axis is zero 2) Two parallel
direction will have quantitatively same Miller Indices 3) two directions ( u v
w ) and ( u2 v2 w2 ) will be perpendicular . If ( u1 u2 + v1 v2 +
w1 w2 ) =0 4) the angle '@' between two intersection direction ( U1
V1 W1 ) and ( U2 V2 W2 ) is given by Density calculation :- 1) volume
density given 2) planner density Planner density is defined as the no. Of
atoms whose Centre are intercepted for unit area of plane under
consideration Note :- In
BCC structure the ( lll) plane will not intersect the Centre of the body
- centred atom hence the body centred atoms should not be consider in the
calculation of planner density on (lll) plane In crystal structure the
planes having highest value of planner density are known as closed pocked plane
or slip planes for example in BCC structure (110) is the closed packed plane
where as the FCC structure (111) is closed packeos plane. 3) Linear density = no. Of atoms / unit
length of direction vector Linear density is defined as the no.
Of atoms where centers are intersect per unit length of a direction
vector

Note :- In crystal structure the direction having highest
value of linear density are called as closed packed direction or slip direction
e. g. In BCC structure (111) is closed pack whereas In FCC structure
(110) is closed packed direction. No.
Of slip system :- No. Of slip system is defined as no.
Of closed packed plane and no. Of closed packed direction No.
Of slip system is an index of density of the material generally maximum
the no. Of slip system more will be ductility of material eg between FCC and
HCP material, FCC material have more no. Of slip system. Hence they are
more ductile however when BCC and FCC material are compared BCC material have
more no. Of slip system , However they do not exhibit ductility
rather they failed in a brittle manner . The reason for brittleness in BCC
solid us Randomness in crientation between neighboring closed packed planes.
Though FCC material have less no. Of slip system than BCC material ,
FCC material exhibits good ductility due to fact that the available slip
system in FCC material are systematically along to facile-ted active are
movement of dislocation

Ductile to brittle transition condition
:- Under the following condition even
criginally ductile material will failed in brittle manner this are called as
ductile to brittle transion condition Low temperature High strain rates In the
presence of surface notches In addition to the above factor the following
factor also caused brittleness in solid. Strain hardening effect caused by cold
working Residual stresses caused by sudden quenching or cold working Presence
of internal nitrate or carbide phase’s Low atomic packing factor Large void volume
Random creation between the closed pack planes etc.

## No comments:

## Post a Comment