Improved phase stability and mechanical properties in Ni-Mn-Sn-B Alloys: Experiments and first-principles calculations

The impact of boron microalloying on the performance of NiMnSn shape memory alloys was investigated using a combination of simulation and experimental methods. The simulation results reveal that B atoms tend to occupy the tetrahedral interstitial positions composed of Ni and Mn. Furthermore, the doping of B atoms not only increases the lattice constant and cell volume of the alloys, but also enhances the phase transition temperature and reduces the thermal hysteresis. The doping of B can enhance the phase stability of austenite and reduce total magnetic moments in the Ni–Mn-Sn alloy. Experimental investigations were conducted on (Ni ₄₃Mn ₄₇Sn ₁₀) _100-XB _X (X=0,1.5,3) alloys, and findings corroborate the simulations, confirming that B element doping elevates the phase transition temperature, lattice constant, and cell volume, while diminishing the thermal hysteresis. Furthermore, boron microalloying contributes to improved mechanical properties. At a B doping level of 3%at, the annealed alloy compressive strength increases by 125%, reaching 578 MPa, with a fracture strain of 6.7%. However the mechanical properties of the as-cast alloy surpass those of the annealed state, with the compressive strength of the same-component cast alloy reaching 1080 MPa, and a fracture strain of 7.9%, marking an 87% improvement over the annealed state.