First-principles density functional theory study of phase transformation in NbCr2 and TaCr2

Hexagonal to cubic phase transformations in the intermetallic Laves-phase compounds NbCr2 and TaCr2 have been studied systematically using the synchroshear deformation mechanism and first-principles density functional theory (DFT). The DFT results provide a quantitative description of the activation energy profiles during the deformation process. By means of these profiles we discuss several transformation possibilities and propose explanations for recent experimental data. In particular it is shown that the synchroshear deformation mechanism should prevail in the two studied Laves phases. Furthermore, the activation energy barriers for TaCr2 are about 17% larger than those for NbCr2. We discuss, how this may lead to the experimentally observed, singnificantly slower transformation kinetic s of TaCr2, compared to NbCr2. Both the observation of fine-scale twins and the originfor the twin formation can be understood as well from the activation energy profiles.