Powder metallurgy fabrication of porous 51(at.%)Ni-Ti shape memory alloys for biomedical applications

Abstract

The effect of time and temperature on the microwave sintering of 51(at.%)Ni–Ti shape memory alloys (SMAs) was investigated in the current research. Furthermore, the microstructure, mechanical properties, and bio-corrosion properties were analyzed based on the sintering conditions. The results revealed that the sintering condition of 700 °C for 15 min produced a part with coherent surface survey that does not exhibit gross defects. Increasing the sintering time and temperature created defects on the outer surface, while reducing the temperature to 550 °C severely affected the mechanical properties. The microstructure of these samples showed two regions of Ni-rich region and Ti-rich region between them Ti2Ni, NiTi, and Ni3Ti phases. The differential scanning calorimeter (DSC) curves of Ni–Ti samples exhibited a multi-step phase transformation B19′–R–B2 during heating and cooling. An increase in the sintering temperature from 550 to 700 °C was found to increase the fracture strength significantly and decreased the fracture strain slightly. Reducing the sintering temperature from 700 to 550 °C severely affected the corrosion behaviors of 51%Ni–Ti SMAs. This research aims to select the optimum parameters to produce Ni–Ti alloys with desired microstructure, mechanical properties, and corrosion behaviors for biomedical applications.