MATERIAL SCIENCE & ENGINEERING

CRYSTAL STRUCTURE & CRYSTAL SYSTEMS

CRYSTAL STRUCTURE IS UNIQUE ARRANGEMENT LEGO OF ATOMS .ARRANGEMENT FORM A UNIT CELL..ATOM ARRANGEMENT PERIODICALLY REPEATED IN 3D.

SEVEN CRYSTAL SYSTEMS: TRICLINIC,MONOCLINIC,ORTHORHOMBIC,TETRAGONAL,TRIGONAL,HEXAGONAL AND CUBIC.

BRAVAIS LATTICE

14 BRAVAIS LATTICE

CUBIC: (3) – SIMPLE CUBIC,FACE CENTERED CUBIC,BODY CENTERED CUBIC

TRICLINIC-1,MONOCLINIC-2,ORTHORHOMBIC-4,TETRAGONAL-2,TRIGONAL-1,HEXAGONAL-1

APF OF BCC CRYSTAL,FCC CRYSTAL

FCC- ATOMS ARE ARRANGED AT THE CORNERS AND CENTER OF EACH CUBE FACE OF THE SHELL.

TOTAL 4 ATOMS IN ONE UNIT CELL

BCC- ATOMS ARE ARRANGED AT THE CORNERS OF THE CUBE WITH ANOTHER ATOM AT THE CUBE CENTER.

2 ATOMS IN UNIT CELL

APF = VOLUME OF ATOMS IN UNIT CELL / VOLUME OF UNIT CELL

STEADY STATE & NON STEADY STATE DIFFUSION PROCESS

NO CHANGES WITH TIME IS STEADY STATE

CONCENTRATION OF SOLUTE ATOM AT ANY POINT IN THE MATERIAL CHANGES WITH TIME IS NON STEADY STATE

ZERO DIMENSIONAL DEFECTS

POINT DEFECTS ARE ZERO DIMENSIONAL : VACANCY,INTERSTITIALITY OR SELF INTERSTITIAL,IMPURITIES IN SOLIDS(SUBSTITUTIONAL,INTERSTITIAL).

FICKS LAW OF DIFFUSION

1ST LAW : FLUX GOES FROM REGIONS OF HIGH CONCENTRATION TO REGIONS OF LOW CONCENTRATION,WITH A MAGNITUDE THAT IS PROPORTIONAL TO THE CONCENTRATION GRADIENT.

2ND LAW:DIFFUSION CAUSE THE CONCENTRATION TO CHANGE WITH TIME.

FRENKEL & SKOTTKY DEFECTS

SCHOTTKY DEFECT : EQUAL NUMBER OF ANIONS AND CATIONS MISSING FROM LATTICE

FRENKEL DEFECT:IONS OF THE LATTICE OCCUPY INTERSTITIAL SITES LEAVING LATTICE VACANT.

HUME ROTHERY RULES

HUME ROTHERY RULES STATE THAT TWO ELEMENTS SHOULD BE VERY SIMILAR TO EACH OTHER TO FORM A SOLID SOLUTION.THE SIMILARITY IS IN CRYSTAL STRUCTURE,ATOMIC SIZE,ELECTRONEGATIVITY,VALENCY

PHASE RULE,NUMBER OF PHASES,COMPONENTS OF DEGREE OF FREEDOM OF A BINARY PHASE DIAGRAM

ACCORDING TO GIBBS PHASE RULE ,THE PHASE IS TO HAVE DENSITY,HARDNESS,CHEMICAL COMPOSITION OF A MATERIAL ARE ESSENTIALLY UNIFORM

P (PHASES)+ F(FREEDOM) = C(COMPONENTS) + 2

BURGERS VECTOR,EDGE & SCREW DISLOCATIONS

THE VECTOR REQUIRED TO COMPLETE THE CIRCUIT OF DISLOCATION IS BURGERS VECTOR. FOR EXAMPLE IN AN EDGE DISLOCATION,BURGERS VECTOR LIES PERPENDICUULAR TO THE LINE OF DISLOCATION.

IN OTHER WORDS BURGERS VECTOR IS REPRESENTED BY THE MAGNITUDE AND DIRECTION OF THE SLIP.

EDGE DISLOCATION IS A LINE DEFECT WHERE AN EXTRA HALF PLAIN OF ATOMS IS INTRODUCED IN MIDWAY THROUGH THE CRYSTAL.

IN SCREW DISLOCATION ,THE MOTION OF DISLOCATION IS PERPENDICULAR TO THE DIRECTION OF STRESS.WHEREAS IN EDGE DISLOCATION,IT IS PARALLEL.

EXTENSIVE SUBSTITUTIONAL SOLID SOLUBILITY

COMPLETE SOLUBILITY OCCURS WHEN THE SOLVENT AND SOLUTE HAVE THE SAME VALENCY.  

DIFFERENCE BETWEEN RANDOM AND ORDERED SOLID SOLUTION

ATOMS OF SOLUTE PRESENT IN THE LATTICE OF THE SOLVENT IS SOLID SOLUTION.

IF ATOMS TAKE PLACE IN PREFEREED SITES,IT IS ORDERED

WHEN IT TAKES RANDOM POSITION IT IS DISORDERED

STATE OF PHASE EQULIBRIUM AND METASTABILITY

THE STATE OF THE SYSTEM DOES NOT PASS TO ANOTHER STATE BECAUSE OF DISTURBANCE.SO IT IS METASTABLE EQUILIBRIUM.SO THE SYSTEM REMAINS IN THE STATE FOR A LONG TIME.

THE OTHER POSSIBLE STATE OF PHASE EQULIBRIUM IS BEING UNSTABLE AND STABLE.

WHY CROSS-SLIP OCCURS IN BCC AND FCC METALS BUT NOT IN HCP METALS

SLIP PLANES DO NOT INTERSECT IN HCP.

SLIP PLANES INTERSECT IN BCC AND FCC ,SO CROSS SLIP CAN OCCUR.

BURGERS VECTOR,DIRECTION OF DISLOCATION LINE

AN EDGE DISLOCATION HAS ITS BURGERS VECTOR PERPENDICULAR TO THE DISLOCATION LINE.

SCREW DISLOCATION MOVES IN A DIRECTION PERPENDICULAR TO THE BURGERS VECTOR.

ROLE OF GRAIN BOUNDARIES AND PRECIPITATE PARTICLES IN STRENGTHENING CRYSTALLINE MATERIALS AGAINST PLASTIC YIELD.

FOREIGN PARTICLES CAN OBSTRUCT MOVEMENT OF DISLOCATIONS WHICH IN TURN STRENGTHENS THE MATERIALS.PRECIPITATION HARDENING INTRODUCES THE FOREIGN PARTICLES.

GRAIN BOUNDARIES MAINTAIN MECHANICAL INTEGRITY AND COHERENCY EVEN DURING DEFORMATION.THAT ALSO OBSTRUCT THE MOVEMENT OF DISLOCATIONS.

WHY CREEP CONSIDERED A HIGH TEMPERATURE PROPERTY

CREEP IS SEVERE IN MATERIALS THAT ARE SUBJECTED TO HEAT FOR LONGER PERIODS AND GENERALLY INCREASES AS THEY NEAR THEIR MELTING POINT.

METALLURGICAL VARIABLES AFFECTING THE CREEP STRENGTH OF A MATERIAL.

EFFECT OF GRAIN SIZE ON THE CREEP STRENGTH OF A MATERIAL

DUCTILE AND BRITTLE FRACTURE

SCHMID’S LAW

HOT AND COLD WORKING

SLIP AND TWINNING

RECOVERY AND RECRYSTALLIZATION