defects of crystals

Download
Share  Add to  Flag Embed
Views:
 
Category: Education
     
 
License:   Some Rights Reserved

Presentation Description

No description available.

Comments

Presentation Transcript

Slide 1:

Crystal Defects

Slide 2:

An ideal crystal can be described in terms a three-dimensionally periodic arrangement of points called lattice and an atom or group of atoms associated with each lattice point called basis. Crystal = Lattice + basis However, there can be deviations from this ideality. These deviations are known as crystal defects.

Slide 3:

Point Defects a)Vacancies/ schottky defect b) Interstitialcies /Frankel defect c)Compositional defects 1) substitutional impurity 2) interstitial impurity d) Electronic defects

Slide 4:

VACANCY OR SHOTTKEY DEFECT

Slide 5:

INTERSTICIALCIES OR FRANKEL DEFECT

Slide 6:

Frenkel defect

Slide 7:

Schottky defect

Slide 8:

In ionic crystals, an ion displaced from a regular site to an interstitial site is called Frankel imperfection.

Slide 9:

A pair of one cation and one anion can be missing from an ionic crystal. Such a pair of vacant ion sites is called schottky imperfection.

Slide 10:

Line Defects Edge dislocation Screw dislocation

Slide 11:

In a perfect crystal, atoms are arranged in both vertical and horizontal planes parallel to the side faces

Slide 12:

A PERFECT CRYSTAL OF VANADIUM

Slide 13:

EDGE DISLOCATION

Slide 14:

If one of these vertical planes does not extend to the full length, but ends in between , within the crystal, it is called edge dislocation .

Slide 15:

1 2 3 4 5 6 7 8 9 1 2 3 4 5 6 7 8 9 slip no slip boundary = edge dislocation Slip plane b Burgers vector

Slide 16:

Burgers vector: The magnitude and the direction of the slip is represented by a vector b called the Burgers vector,

Slide 17:

Screw Dislocation Line b t b || t 1 2 3

Slide 18:

If a plane ends abruptly inside a crystal we have a defect . The whole of abruptly ending plane is not a defect Only the edge of the plane can be considered as a defect This is a line defect called an EDGE DISLOCATION

Slide 19:

1 2 7 6 5 4 3 8 9 1 8 2 3 4 5 6 7 9 10 11 12 13 1 2 3 4 5 6 7 8 9 1 8 2 3 4 5 6 7 9 10 11 12 13 A closed Burgers Circuit in an ideal crystal S F 14 15 16 14 15 16

Slide 20:

1 2 7 6 5 4 3 8 9 1 8 2 3 4 5 6 7 9 10 11 12 13 14 15 1 2 3 4 5 6 7 9 1 2 3 4 5 6 8 7 9 10 11 12 13 14 15 8 16 S b 16 RHFS convention F  Map the same Burgers circuit on a real crystal

Slide 21:

Glide of an Edge Dislocation  crss  crss  crss is critical resolved shear stress on the slip plane in the direction of b.

Slide 22:

Surface Defects

Slide 23:

SCREW DISLOCATION

Slide 24:

SCREW DISLOCATION

Slide 25:

BURGERS VECTORFOR SCREW DISLOCATION

Slide 26:

TWIN BOUNDARY

Slide 27:

GRAIN BOUNDARY

Slide 28:

TILT BOUNDARY

Slide 29:

Grain 1 Grain 2 Grain Boundary Internal surface: grain boundary A grain boundary is a boundary between two regions of identical crystal structure but different orientation

Slide 30:

Grain Boundary: low and high angle One grain orientation can be obtained by rotation of another grain across the grain boundary about an axis through an angle If the angle of rotation is high, it is called a high angle grain boundary If the angle of rotation is low it is called a low angle grain boundary

Slide 31:

Stacking fault C B A C B A C B A A C B A B A C B A Stacking fault FCC FCC HCP

Slide 32:

A twin boundary happens when the crystals on either side of a plane are mirror images of each other. The boundary common to the two planes is a twin boundary