On discussion of the applicability of local Avrami exponent: Errors and solutions

The local Avrami exponent is usually used to evaluate nonlinear Kolmogorov-Johnson-Mehl-Avrami (KJMA) plots. But in some phase transformations, a changing kinetic exponent may result from the inappropriate use of kinetic model. A modified kinetic model considering the impingement effect has been introduced to show that when the KJMA equation is inapplicable for kinetic analysis the local Avrami exponent may have errors and a modified form of the local Avrami exponent thus can solve this problem. Using four theoretical transformations with different impingement factors as examples, we have shown how the errors of calculated kinetic exponent values are produced, and how this problem can be avoided with a modified form of the local Avrami exponent.