The role of phase compatibility in martensite

TL;DR

This paper investigates how phase compatibility affects the microstructure and thermal hysteresis in shape memory alloys, using phase field simulations and experimental validation, highlighting the importance of coupling phase transformation with plasticity.

Contribution

It introduces a 3D phase field model for martensitic transformation in TiNiPd alloys and links phase compatibility to hysteresis reduction and microstructure stability.

Findings

Simulation results agree with TEM observations.

Phase compatibility reduces thermal hysteresis.

Coupling with plasticity explains hysteresis behavior.

Abstract

Shape memory alloys inherit their macroscopic properties from their mesoscale microstructure originated from the martensitic phase transformation. In a cubic to orthorhombic transition, a single variant of marten- site can have a compatible (exact) interface with the austenite for some special lattice parameters in contrast to conventional austenite/twinned martensite interface with a transition layer. Experimentally, the phase compat- ibility results in a dramatic drop in thermal hysteresis and gives rise to very stable functional properties over cycling. Here, we investigate the microstructures observed in Ti50Ni50-xPdx alloys that undergo a cubic to orthorhombic martensitic transformation using a three dimensional phase field approach. We will show that the simulation results are in very good agreement with transmission electron microscopy observations. However, the understanding of the drop in thermal hysteresis requires the coupling of phase transformation with plastic activity. We will discuss this point within the framework of thermoelasticity, which is a generic feature of the martensitic transformation.