Mechanical properties and corrosion resistance of porous nickel titanium alloys synthesized in different reactive atmospheres

In the existing studies on the self-propagating high temperature synthesis of titanium nickelide, the main attention has been paid to the study of the influence of heating rate, synthesis start temperature, powder particle size, reaction gas pressure on the structure and properties of NiTi intermetallides. However, the influence of the reactive medium on the formation of surface intermetallic oxynitrides and the properties of the NiTi alloys has not been considered. In the present work, porous titanium nickelide alloys have been obtained by self-propagating high-temperature synthesis in two different reactive atmospheres, argon and nitrogen. The studies show that NiTi-(N) alloys synthesised in the nitrogen reaction atmosphere contain a large amount of brittle secondary Ti2Ni+Ti4Ni2O(N) phases which, in contrast to NiTi-(Ar), are predominantly distributed as small particles. The intergranular Ti2Ni phases in the NiTi-(Ar) alloy synthesised in the argon reaction atmosphere are observed as regions of extensive accumulation of Ti2Ni phase. The reactive nitrogen environment resulted in dispersion of the Ti2Ni phase and lower compressive strength of the porous NiTi-(N) alloy compared to NiTi-(Ar). However, both alloys have a compressive strength greater than human cancellous bone and can be successfully used for intraosseous implantation. At the same time, the porous alloys obtained in different reaction media are passive to electrochemical corrosion and resistant to dissolution in biological media containing chlorine.