Thursday, 8 March 2018

MATERIAL SCIENCE

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. 


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