HREM study of self-accommodated thermal ε-martensite in an FeMnSiCrNi shape memory alloy

Abstract

An FeMnSiCrNi shape memory alloy containing 70% of thermal ε-martensite has been studied using high resolution electron microscopy. Images recorded along a 〈011〉 γ//〈2110〉 ε axis show, at the atomic level, that large ε-bands have a layered substructure and consist of thin ε-layers separated by layers of untransformed austenite. The structure of the ε (h.c.p.)/γ (f.c.c.) interface at the ε-layer tips has been determined by using both the analysis of numerically filtered images and isotropic elasticity calculations: it can be described as a periodic array of 30° and 90° Shockley partials in a 2:1 proportion. This model illustrates the self-accommodation properties of thermal ε-martensite at the finest scale and explains the easy reversion of the hexagonal phase.