Orientation dependence of the martensitic transformation in (Zr,Mg)O2 embedded in a TRIP steel matrix

Metal matrix composites (MMCs) consisting of austenitic TRIP (TRansformation Induced Plasticity) steel reinforced by Mgstabilized zirconia (Zr,Mg)O-2 show martensitic phase transformations in both constituents during compressive deformation. The influence of the crystallographic orientation of individual (Zr,Mg)O-2 particles on the capability of their stress-assisted martensitic transformation from tetragonal to monoclinic phase with respect to the external load was elucidated. The corresponding amount of the resulting axial compressive strain was calculated for all possible crystallographic orientations of the tetragonal phase, and correlated to the evolving fractions of m-(Zr,Mg)O-2. In order to obtain the local crystallographic orientation and to identify the respective zirconia phase, the as-sintered material and a 25% compressed sample were examined by electron back-scatter diffraction (EBSD). After compressive deformation, up to 80% of the individual particle volume exhibited band-like structures containing m-(Zr,Mg)O-2. The progress of the martensitic phase transformation was found to depend on the local crystallographic orientation of t-(Zr,Mg)O-2 with respect to the load direction, although this effect is strongly influenced by the morphology of individual particles. (C) 2015 The Authors. Published by Elsevier Ltd.