Shape memory deformation mechanisms of Ru-Nb and Ru-Ta shape memory alloys with transformation temperatures

Ru-based high temperature shape memory alloys show different structures at different temperatures and composition. Equiatomic Ru-Ta and Ru-Nb show two subsequent phase transformations, but their individual influence is still unclear because of the difficulty of comparing the high temperature cubic phase, the intermediate tetragonal phase and the low temperature monoclinic phase. It is important to find a way to compare these structures in order to better understand the microstructure of these alloys and their shape memory behaviour. In order to get the necessary information the alloys have been investigated with neutron diffraction technique during in-situ heating up to about 1100 degrees C. This study shows the evolution of the lattice parameters and the shape of the unit cells at different temperatures for the three phases these materials exhibit. It proposes a way to compare the different structures and it gives a mathematical expression of the phase transformations. The ultimate goal of this work is to enable a better understanding of the deformation mechanisms in the unit cell and a possible anticipation of the existence of a shape memory effect in these systems. (C) 2014 Elsevier Ltd. All rights reserved.