a) For a given material, would you expect the surface energy to be greater than, the same as, or less than the grain boundary energy? Choose the answer for part (a) from the menu in accordance to the question statement (b) Is the grain boundary energy of a small-angle grain boundary less than for a high-angle one? (yes or no)

Answer / Explanation:

To properly answer this question, let us define what a grain boundary is:

A grain boundary is the interface between multiple grains or crystals in a poly-crystalline material. They could also be refereed to as defects in the crystal structure and tend to decrease the electrical and thermal conductivity of structures.

Now, if we refer back to the question asked,

(a) The surface energy is grater than the grain boundary energy because surface atom have fewer bonds than atom along a grain boundary.

Consequentially, the lower the number of bonds formed, the higher the energy

(b) A higher angle grain boundary has higher misalignment and hence greater disruption of bonds (lesser number of bonds) than a small angle grain boundary. Therefore, a high angle grain boundary has higher energy.