quiz 2 - defects

• Vacancy

• Impurity

Types of Point Defects

Dislocations

• Edge Dislocation

• Screw Dislocation

• Mixed Dislocation

Types of Line Defects

• Grain Boundaries

• Surfaces

• Twin Defecta

• Stacking Fault

Planar Defects

• Pores and Voids

• cracks

• foreign inclusions

Volume defects

Point defects

Irregular or deviations from ideal arrangement around a point or an atom in a crystalline substance

Vacancy

Defect where an atom is missing from an atomic site

Vacancy

This occurs due to imperfect packing during crystallization

Vacancy

This defect results in a decfease in density of a substance

Interstitial

This defect is the addition of extra atom within a crystal structure and causes atomic distortion which leads to an increase of the density of the substance

Impurity defects

Also called extrinsic defects. This is when there is an impurity which are atoms are different from the host

• Size difference bet. solute and solvent must be < 15%

• Electronegativity must be comparable

• Valence must be similar

• Crustal structures should be the same

Rules for complete solid solution

• Solidification

• Heating

• Stress

Origin of point defects

Line defects

irregularities or deviation from ideal arrangement in entire rows of lattice points

Line defects

Defect that is produced due to the misalignment of atoms in a crystal lattice

Line defects

Also known as dislocation which causes mechanical deformation

Edge Dislocation

Causes by termination of a plane of atoms in the middle of a crystal where adjacent planes are not straight but instead bend around the edge of the terminating plane which results in increase of density of the substance

Screw Dislocation

Defect in which atoms are not arranged in a line but in a form of a screw thread which spirals down from one end to another in a form of a helix

Mixed dislocation

Has both edge and screw character

• free surface

• boundaries (grain, interphase)

• another dislocation

Dislocations can never terminate within a crystal. It can terminate at:

Planar defects

Defects associated with boundaries that are separate regions of materials and have different crystal structure

Planar defects

Defects with two dimensional effect which is due to the change in the orientation of the atomic planes and stacking sequence of atomic planes

Grain boundaries

Defects that occurs in the boundaries between crustals produced by solidification process

Grain boundaries

Defect that causes a change in crystal orientation across and impede dislocation motion

Ability of dislocations to move

The ability of a metal to deform depends on what

Restricting dislocation motion

What makes the material stronger?

• changes in direction of slip plane

• disorder at grain boundary

dislocations cannot easily cross grain boundaries because?

Surfaces

Type of planar defects where atoms at the surface lack required coordination number

Twin defect

Planar defect that refers to a change in crystal orientation which lead to formation of mirror image of a crystal across a plane

Stacking fault

Planar defects that refers to anomalies in the stacking sequence of crystal planes that disrupt the continuity of a perfect lattice

Pores and voids

volume defect that refers to trapped gases which decreases mechanical strength

Cracks

refers to local discontinuity produced by fracture

foreign inclusions

undesirable foreign particles