  The Kolmogorov-Johnson-Mehl-Avrami model for isothermal transformation
kinetics is universal under specific assumptions. However, the experimental
Avrami exponent deviates from the universal value. In this context, we study
the effect of transient heterogeneous nucleation on the Avrami exponent for
bulk materials and also for transformations leading to nanostructured
materials. All transformations are assumed to be polymorphic. A discrete
version of the KJMA model is modified for this purpose. Scaling relations for
transformations under different conditions are reported.
