Kinetic Theory of the Overlapping Phase Transformations

TL;DR

This paper develops a kinetic theory framework based on the Avrami model to analyze overlapping phase transformations in steels and alloys, enabling characterization of multiple concurrent precipitation processes.

Contribution

It introduces a method to characterize simultaneous precipitation processes and their interference effects during isothermal transformations using kinetic parameters.

Findings

Able to distinguish overlapping precipitation processes

Provides a way to compute individual kinetic parameters

Accounts for interference effects between processes

Abstract

Often a number of precipitation processes in steels and alloys occur simultaneously (they have the same origin in time) albeit at different rates. Consequently, isothermic transformations are accompanied, in this case, by the occurrence of second processes of precipitation that influence the changes of the macroscopic parameter chosen for the kinetic study while first processes are occurring. In this context a set-up is presented that addresses the issue of characterization of nucleation and growth mechanisms of the individual processes. Soft and hard interferences of processes are considered. The present approach is based on the Avrami model and allows computing the kinetic parameters (n, k) of the different precipitation processes in isothermic phase reactions.