Surface defects can occur at grain boundaries, which separate grains of different crystallographic orientation. Twin boundaries have atomic arrangements on one side that are reflections of the other side, and the orientation change of one boundary is restored by another. Stacking faults interrupt the proper order of stacking planes, such as the ABCABCA sequence that produces a cubic face-centered crystal structure.

1. Surface Defects
Surface defects may arise at
the boundary between two
grains.
1- Grain boundary
The boundary separates two
small grains having different
crystallographic orientation.

2. 2- Twin Boundry
The atomic arrangement on
one side of twin boundary
is the reflection of
arrangement on other side
of twin.
The orientation change
introduced by oneboundry
is restored by another.

3. 3-Stacking Faults
Briefly describe the concept
Defects in which the proper
order of stacking planes is
interrupted.
The stacking sequence ABCABCA...
produces a cubic face-centered crystal.