Avrami exponent under transient and heterogeneous nucleation transformation conditions

TL;DR

This paper investigates how transient and heterogeneous nucleation affect the Avrami exponent in transformation kinetics, especially in polymorphic transformations, by modifying the KJMA model and deriving scaling relations.

Contribution

It introduces a modified discrete KJMA model to account for transient heterogeneous nucleation effects in transformation kinetics.

Findings

Derived scaling relations for different transformation conditions

Showed deviations of Avrami exponent from universal value due to heterogeneity

Applicable to bulk and nanostructured polymorphic transformations

Abstract

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.