Group Members.

Tayyaba Anum Javed MME-10M-35

Mehvish Tariq MME-10M-34

CRYSTAL DEFECTS.The distortion in the periodic structure of the

individual

grains of crystals are defined as crystal defects. Such as:

• Point Defect

• Line Defect

• Planar Defect

• Volumetric Defect

POINT DEFECT.• “ Point defects are where an atom is missing or at an

irregular place in lattice structure” In pure metal two types of point defects are possible:• Intrinsic• Extrinsic Intrinsic point defect are of two types:• Vacancy • Self Interstitial Atoms The vacancy has been formed by the removal

of an atom from an atomic site and the interstitials by introduction of an atom from a non-lattice site

Extrinsic point defect is present in the lattice having impurity atoms. Impurity atom can take up two different types of sites:

Substitution impurity atomInterstitial impurity atom Substitution impurity atom, is an impurity

atom which replace the parent atom in the lattice at lattice site. Where as, Interstitial impurity atom, is an atom of impurity at a non-lattice site.

Point defect produce local distortions in perfect lattice. The amount of distortion depends upon the amount of space between the atoms and the size of the atoms.

LINE DEFECT.Defect that is produced due to the misalignment of atoms

in a crystal lattice.Line defect produces two types of dislocations;Edge dislocationScrew dislocation Edge dislocations are caused by the termination of a

plane of atoms in the middle of a crystal. The adjacent planes are not straight, but instead bend around the edge of the terminating plane so that the crystal structure is

perfectly ordered on either side.

If the misalignment shifts a block of ions gradually downwards or upwards causing the formation of a screw like deformation, a screw dislocations is formed.

PLANAR DEFECT.• In planar defect, boundaries or planes are formed,

separate the structure into regions, having the same crystal structure but different orientation.

• Planar defects include:Stacking faultsGrain boundariesTwin boundaries

• Stacking faultsIn FCC structure, two types of stacking faults are

present;.

IntrinsicExtrinsic

The stacking sequence in HCP structure is ABABAB… So, if the HCP structure is going along as ABABAB and suddenly switches to ABABABCABAB, there is a stacking fault present.

• Grain boundariesThe grain boundaries defect may develop when

the arrangement of the atoms in each grain is identical but with different orientations.

Twin boundariesA twin boundary is a plane, across which there is a

special mirror image miss orientation of the crystal structure. The twin boundaries can be produced when a shear force acting along the boundary, causes the atoms to shift out of position.

VOLUMETRIC DEFECTS.Volumetric defects occur on a much bigger scale than the

rest of the crystal defects. Voids, porosity and precipitates are the volumetric

defects.Voids are regions where there are a large number of atoms

missing from the structure. Voids can occur for a number of reasons.

When voids occur, due to air bubbles which trapped, when a material solidifies, is commonly called porosity.

Another type of volumetric defect occurs, when impurity atoms cluster together to form small regions of a different phase. That is another form of volumetric defect.

•Volumetric defect due to porosity