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 Ni 2 Mn 1.5− x Cu x Ti 0.5 ( x = 0.125, 0.25, 0.375, 0.5) and Ni 2− y Co y Mn 1.5− x Cu x Ti 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 Ni 2 Mn 1.5− x Cu x Ti 0.5 and Ni 2− y Co y Mn 1.5− x Cu x Ti 0.5 ( y < 0.625) alloys. When y = 0.625 in the Ni 2− y Co y Mn 1.5− x Cu x Ti 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.