5. Explain briefly ALL of the following observations (a) For some systems, decomposition of a solid solution into two product phases can occur without requiring nucleation of the new phase. (b) A precipitate population will continue to evolve during heat treatment even after the equilibrium volume fraction has been reached. (c) Martensitic transformations can be reversible, whereas diffusional transformations are not. (d) A deformed metal when annealed first shows a gradual reduction in hardness with increasing time followed by sharp hardness reduction as annealing continues