First-principles study of the martensitic transformation in pressure of the all-d d-metal Heusler alloy Fe2NbIr

The martensitic transformation of the new all-d d-metal Heusler alloy Fe2NbIr is investigated using first-principles. The structure undergoes softening and hardening under pressure, which corresponds to the two phases of the martensitic phase transformation, i.e. C ' softening of the austenite and C ' hardening of the pre-martensite phase, implying that the pressure may induces to produce a cubic pre-martensite phase. An exciting phenomenon is found in the tetragonal deformation of the pre-martensite phase, where the pre-martensite phase overcome the energy barrier of the jump to produce a tetragonal martensite phase with a much lower energy. It explains the presence of a pre-martensite phase in shape memory alloys, i.e., it provides a conduit for the phase change. This work presents an analysis of the anomalous softening behaviour of Fe2NbIr and the mechanism of the pressure- induced martensitic transformation, and provides a new idea for study of the precursor effect of martensitic phase transformation.