Effect of lattice mismatch-induced strains on coupled diffusive and displacive phase transformations

TL;DR

This study uses phase-field modeling to explore how lattice mismatch-induced strains influence the interplay of diffusive and displacive phase transformations, affecting microstructure evolution and transformation diagrams in alloys.

Contribution

It introduces a phase-field model that captures the effects of coherency strains on coupled diffusive and displacive transformations, revealing their impact on microstructure stability and transformation diagrams.

Findings

Coherency strains can stabilize mixed microstructures.

Small volume change differences significantly affect martensite formation.

The model predicts competitive or cooperative nucleation of phases.

Abstract

Materials which can undergo slow diffusive transformations as well as fast displacive transformations are studied using the phase-field method. The model captures the essential features of the time-temperature-transformation (TTT) diagrams, continuous cooling transformation (CCT) diagrams, and microstructure formation of these alloys. In some materials systems there can exist an intrinsic volume change associated with these transformations. We show that these coherency strains can stabilize mixed microstructures (such as retained austenite-martensite and pearlite-martensite mixtures) by an interplay between diffusive and displacive mechanisms, which can alter TTT and CCT diagrams. Depending on the conditions there can be competitive or cooperative nucleation of the two kinds of phases. The model also shows that small differences in volume changes can have noticeable effects on the early stages of martensite formation and on the resulting microstructures. -- Long version of cond-mat/0605577 -- Keywords: Ginzburg-Landau, martensite, pearlite, spinodal decomposition, shape memory, microstructures, TTT diagram, CCT diagram, elastic compatibility