Research progress in Ti-Ni-Hf high temperature shape memory alloys

Ti-Ni-Hf alloy is one of the most potential high temperature shape memory alloys due to the various advantages such as higher phase transformation temperature, relatively lower cost and larger output work. However, the plastic deformation takes place prior to the reorientation of martensitic variants due to the lower matrix strength, which results in the poor shape memory properties. To date, the measures of improving the strain recovery characteristics consist of thermo-mechanical treatment (cold rolling + annealing), alloying, aging treatment and fabrication of single crystal etc. It has been revealed that the strain recovery performances of Ti-Ni-Hf alloys are closely related to the microstructural features. In the present paper, the recent progress in the field of Ti-Ni-Hf high temperature shape memory alloy was presented, mainly consisting of microstructural evolution, martensitic transformation behaviour, mechanical properties and strain recovery features, moreover, the relationship between the microstructure, martensitic transformation as well as the mechanical and strain recovery characteristics was established, based on the previous research results. At present, the poor cold or hot workability of Ti-Ni-Hf high temperature shape memory alloy is the bottleneck which limits its extensive applications. Hence, the future research may focus on the powder metallurgy and additive manufacturing of Ti-Ni-Hf high temperature shape memory alloy