Interplay between diffusive and displacive phase transformations: TTT diagrams and microstructures

TL;DR

This paper uses a Ginzburg-Landau model to explore how fast displacive and slow diffusive phase transformations interact, predicting microstructure formation and TTT diagrams in alloys like steel.

Contribution

It introduces a simple phase-field model that captures the interplay between diffusive and displacive transformations, explaining mixed microstructures in steels.

Findings

Model predicts formation of mixed microstructures such as martensite-retained austenite.

Intrinsic volume changes stabilize specific microstructures.

The approach explains the existence of martensite finish temperature.

Abstract

Materials which can undergo extremely fast displacive transformations as well as very slow diffusive transformations are studied using a Ginzburg-Landau framework to understand the physics behind microstructure formation and time-temperature-transformation (TTT) diagrams. This simple model captures the essential features of alloys such as steels and predicts the formation of mixed microstructures by an interplay between diffusive and displacive mechanisms. The intrinsic volume changes associated with the transformations stabilize mixed microstructures such as martensite-retained austenite (responsible for the existence of a martensite finish temperature) and martensite-pearlite. keywords: phase-field, spinodal decomposition, pearlite, martensite, steel, elastic compatibility