Define Grain, Grain Boundary and Characteristics of Grain and Grain Boundary

Grain and Grain Boundary:

The Poly-Crystalline metals which has different types of shapes called grains. Poly-Crystalline metals are formed by crystals which are form by the transition of liquid to solid.
The individual grains which are separated is called grain boundaries. In this, the grains are Regularly packed.
This boundary is formed after complete solidification.

Characteristics of Grain and Grain Boundary:

Grains with more than six or six will grow and less than the six will get to shrink and consumed into larger grains.
To join the larger grains the shrink to migrate at the boundary.
The grain growth impedes with the help of second phase particles.
For many types of impurities the grain boundaries are preferential, and by this weakening can occur.
Grain interiors are weaker than grain boundaries when it is under room temperature and it causes to failure by themselves.
In this at high temperature the coarse grain structure is desirable. and grain boundary becomes weak.