Volume-change martensitic transformation and good ductility in all-d-metal Ni2-based Heusler alloys

Using the first-principles calculation method based on density functional theory, we developed a new class of Ni2-based all-d-metal magnetic shape memory alloys (MSMAs). We discussed the competition among L21, XA, and B2 cubic structures for the ground state in all investigated Ni2YZ (Y = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn; Z = Pd and Pt) alloys by analyzing the total energy differences and charge density differences. We calculated the formation energies to assess the feasibility of the experimental preparation of these alloys. Through a comprehensive analysis of the total energy differences between austenite and martensite, the density of states, and the bulk mechanical properties, we found that Ni2YZ (Y = Sc, Ti, V, Cr, Mn, Fe, and Zn; Z = Pd and Pt) alloys are prone to undergoing a martensitic transformation. All these all-d-metal alloys exhibit volume shrinkage during the transition from austenite to martensite, with some alloys experiencing a volume change of over 1%. The calculated Pugh's ratio, Cauchy pressure, and Poisson's ratio consistently indicate that all Ni2YZ (Y = Sc, Ti, V, Cr, Mn, Fe, and Zn; Z = Pd and Pt) alloys have better ductility than the conventional MSMA Ni2MnGa. Therefore, our study is expected to inspire the design and application of new all-d-metal MSMAs.