Surface defects

          Surface defects are the two dimensional regions in a crystal. The defect which takes place on the surface of a material is known as surface defects. It may be noted that surface defects takes place either due to imperfect packing of atoms during crystallisation or defective orientation of the surface. The types of surface defects are:

1) External defects

2) Internal defects

External defects

          The external surface of a material is an imperfection itself because the atomic bonds do not extend beyond it. The surface atoms have neighbor on one side only while atoms inside the crystal have neighbors on either side of them. Since surface atoms are not entirely surrounded by others, they possess higher energy than that of internal atoms. For most metals, the energy of surface atoms is of the order 1 J/m2.

Internal defects

The internal defects are classified as follows:

1. Grain boundaries
2. Twin boundaries
3. Tilt boundary