Surface defects in crystals
The document discusses various types of surface defects that can occur in crystals, including external surfaces, grain boundaries, tilt boundaries, twist boundaries, twin boundaries, and stacking faults. External surfaces have unsatisfied atomic bonds and higher surface energy than bulk atoms. Grain boundaries are regions between two adjacent grains that are slightly disordered with low density and high mobility. Tilt boundaries appear as arrays of edge dislocations when grains are misaligned with a parallel rotation axis. Twist boundaries have a perpendicular rotation axis and form as arrays of screw dislocations for low angle grain boundaries. Twin boundaries are mirror images of atomic arrangements across the boundary formed by shear deformation. Stacking faults are imperfections in the stacking sequence of atomic planes in crystals.
Surface defects in crystals
- 1. SURFACE DEFECTS IN CRYSTALS presented by: Arun K S Ist sem M.Tech Sjcet, palai
- 2. Surface Defects 1.External Surface: Surface atoms have unsatisfied atomic bonds, and higher surface energies, than the bulk atoms. To reduce surface free energy, material tends to minimize its surface areas against the surface tension (e.g. liquid drop). 2.Grain boundaries: regions between two adjacent grains slightly disordered low density in grain boundaries high mobility high diffusivity
- 3. 3.Tilt Boundary: A Tilt Boundary, between two slightly mis-aligned grains appears as an array of edge dislocations. Rotation axis is parallel to the boundary plane 4. Twist Boundary: Rotation axis is perpendicular to the boundary plane Low angle grain boundaries, that appear as an array of Screw dislocations.
- 4. 5.Twin boundaries: These are the boundaries in the grains at which the atomic arrangement on one side of the boundary is the mirror image of the atoms on the other side . May be produced by shear deformation. The region between the pair of boundaries is called the twinned region.
- 5. 6.Stacking Faults: Formed by fault in the stacking sequence of atomic planes in crystals. Considering stacking arrangement in FCC: ABCABCABCABCABC ABCABC BCABCABC This thin region is a surface imperfection and is called Stacking faults.
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