First-principles calculations of Ni–(Co)–Mn–Cu–Ti all-d-metal Heusler alloy on martensitic transformation, mechanical and magnetic properties

The martensitic transformation, mechanical, and magnetic properties of the Ni₂Mn_1.5−xCu_xTi_0.5 (x = 0.125, 0.25, 0.375, 0.5) and Ni_2−yCo_yMn_1.5−xCu_xTi_0.5 (x = 0.125, y = 0.125, 0.25, 0.375, 0.5) and (x = 0.125, 0.25, 0.375, y = 0.625) alloys were systematically studied by the first-principles calculations. For the formation energy, the martensite is smaller than the austenite, the Ni–(Co)–Mn–Cu–Ti alloys studied in this work can undergo martensitic transformation. The austenite and non-modulated (NM) martensite always present antiferromagnetic state in the Ni₂Mn_1.5−xCu_xTi_0.5 and Ni_2−yCo_yMn_1.5−xCu_xTi_0.5 (y < 0.625) alloys. When y = 0.625 in the Ni_2−yCo_yMn_1.5−xCu_xTi_0.5 series, the austenite presents ferromagnetic state while the NM martensite shows antiferromagnetic state. Cu doping can decrease the thermal hysteresis and anisotropy of the Ni–(Co)–Mn–Ti alloy. Increasing Mn and decreasing Ti content can improve the shear resistance and normal stress resistance, but reduce the toughness in the Ni–Mn–Cu–Ti alloy. And the ductility of the Co–Cu co-doping alloy is inferior to that of the Ni–Mn–Cu–Ti and Ni–Co–Mn–Ti alloys. The electronic density of states was studied to reveal the essence of the mechanical and magnetic properties.