Phase-field study of size-dependent morphology of austenite-twinned martensite interface in CuAlNi

Size-dependent microstructure of the interface layer between austenite and twinned martensite is studied using a recently developed finite-strain phase-field model. The microstructure is assumed periodic and two-dimensional, however, non-zero out-of-plane displacements are allowed so that the basic microstructural features, specifically the nominal orientation of the twinning and habit planes and the twin fraction, are consistent with the crystallographic theory of martensite. The phase-field computations are carried out for the CuAlNi shape memory alloy undergoing the cubic-to-orthorhombic transformation, and the corresponding four crystallographically distinct microstructures of the austenite-twinned marten site interface are studied in detail. The focus is on size-dependent morphology of the interface layer and on size-dependent interfacial and elastic micro-strain energy contributions. Two mechanisms of reducing the elastic micro-strain energy are revealed: formation of a non-planar zigzag-like interface and twin branching. (C) 2016 Elsevier Ltd. All rights reserved.