Modeling size and orientation effects on the morphology of microstructure formed in martensitic phase transformations using a novel discrete particle model

Abstract

The morphology of fine microstructure arising from reversible martensitic transformations is known to depend on the sample size and orientation to applied thermal or mechanical loading. In this paper we study these effects using a novel discrete particle approach. Our new approach uses a multibody interparticle interaction for the discrete particles which is obtained directly from a polyconvex continuum free energy appropriate for such materials. In order to study the interfaces between the austenite and martensite phases, the material is subjected to a temperature gradient. A competition between self-accommodation which causes formation of twinned martensite and the requirement of compatibility of the phases on the interfaces results in very distinctive microstructures. We study the effect of the angle between the applied temperature gradient and the orientation of the parent phase on the phase boundary. In smaller samples, a phase boundary between austenite and a single variant of martensite forms due to the effect of the free surface and the resultant microstructure takes a banded form. Detwinning under applied mechanical loading is strongly dependent on the initial microstructure. The implicit kinetic relation for twin boundary propagation of this approach shows a classical stick-slip form.