Fabrication of nickel-titanium-iron shape memory alloys by powder metallurgy route and analyses of their physical and mechanical behaviour

Abstract

In this research work, the effect of Fe additions on the phase evolution, microstructure, chemical composition, transformation behaviour and properties of Ni (50−X) Ti 50 Fe X shape memory alloys has been investigated. The elemental Ti, Ni and Fe mixed powders are compacted at 600 MPa, followed by sintering at 1100°C for 4hr in an Ar atmosphere. Phase analysis and microstructural studies confirmed the presence of the NiTi phase besides other Ni-rich and Ti-rich phases. The 8at.-% Fe sample shows higher relative density, lower porosity, higher hardness, higher elastic modulus and higher wear resistance owing to the presence of a higher amount of secondary intermetallic phases compared to other composition samples. Interestingly, the 4at.-% Fe sample has a higher percentage of NiTi (B19') phase and shows a better shape memory effect and elastic recovery than other composition samples. FESEM morphology of worn surface explained various wear mechanisms with respect to shape memory behaviour.