Preparation and characterization of porous NiTi alloys synthesized by microwave sintering using Mg space holder

To obtain the lightweight, high strength, and high damping capacity porous NiTi alloys, the microwave sintering coupled with the Mg space holder technique was employed to prepare the porous NiTi alloys. The microstructure, mechanical properties, phase transformation behavior, superelasticity, and damping capacity of the porous NiTi alloys were investigated. The results show that the porous NiTi alloys are mainly composed of the B2 NiTi phase with a few B19′ NiTi phase as the sintering temperature is lower than or equal to 900 °C. With increasing the sintering temperature, the porosities of the porous NiTi alloys gradually decrease and the compressive strength increases first, reaching the maximum value at 900 °C, and then decreases. With increasing the Mg content from 1 wt.% to 7 wt.%, the porosities of the porous NiTi alloys increase from 37.8% to 47.1%, while the compressive strength decreases from 2058 to 1146 MPa. Compared with the NH₄HCO₃ space holder, the phase transformation behavior of the porous NiTi alloys prepared with Mg space holder changes, and all of the compressive strength, superelasticity, shape memory effect and damping capacity are greatly improved.