PPT Slide
3. At high temperatures the grain boundaries function as sites of weakness.
Grain boundary sliding may occur, leading to plastic flow and/or opening up of voids along the boundaries.
4. Grain boundaries can act as sources and sinks for vacancies at high temperatures, leading to diffusion currents as, for example, in the Nabarro Herring creep mechanism.
5. In polycrystalline materials, the individual grains usually have a random orientation with respect to one another.