Unraveling the physical and mechanical properties of 4 O modulated martensite in Ni-Co-Mn-Sb magnetic shape memory alloys

Ni-Mn-Sb alloy has attracted much attention due to its low cost and excellent magnetic properties. To enhance the magnetic moment difference of the alloy, the fractional substitution of Co for Ni in Ni-Mn-Sb alloys is an effective strategy. And there is little research on modulated martensite closely related to excellent magnetic properties. Therefore, we systematically investigated the influences of Co-doping on the physical and mechanical properties of four-layered orthorhombic modulated martensite (4 O) in Ni24-xCoxMn18Sb6 (x = 0, 1, 2, 3, 4, 5, 6) alloys by the first principles calculations. Key results demonstrate that the phase stability of 4 O phase decreases with the increase of Co concentration. At the same time, the phase transition temperature from austenite (A) to 4 O phase significantly decreases. The sensitivity of the phase transition temperature from A to 4 O phase to the components is not as high as the phase transition temperature from A to non-modulated martensite (NM) phase. The magnetic moment difference between A and 4 O increases sharply at x = 6. In terms of mechanical properties, Co-doping helps to enhance the mechanical stability and the anisotropy of 4 O phase. The origin of the above phenomena was explained through the density of states. The above results can provide useful information for optimizing the performance of multivariate shape memory alloys.