Structural evolution during recrystallization

The evidence showing the failure of the classic Johnson-Mehl-Avrami equation to describe most recrystallization kinetics is reviewed. The failure is seen in the value of the exponent in which is less than the theoretically predicted exponents. The reason for this failure is at least in part due to the non-random distribution of nucleation sites. This non-random distribution seems to arise from the grain to grain variation in deformation microstructure. Simple 3-dimensional and more precise 2-dimensional models of the recrystallization kinetics are presented which demonstrate that variation in the stored energy, on the scale of the grain size, does lead to the range of JMA exponents seen experimentally. The importance of this for the resulting grain size distribution is indicated.