1. Which is easier for nucleation in solids, homogeneous or heterogeneous nucleation? What are the common defects present in solid solution (list at least five kinds of defects)?  Are the defects generally harmful for nucleation and explain why? 

 

2. The following figure shows the phase diagram and the corresponding homogeneous nucleation rates of composition X₀ at different temperatures. T_e indicates the equilibrium temperature for ???? and ???? at X₀.

 

Explain why the peak of nucleation rate happens at a temperature lower than T_e 

 

3. For the following nucleation on grain boundaries, if misfit train energy can be ignored, how the optimum embryo shape is determined? What is the condition to achieve mechanical equilibrium for such an embryo shape? Can you derive the excess free energy associated with the embryo (using the defined interface energy and interface area A) ?

 

 

Te T Te T T + 0 0 N N