The microstructure design and strain recovery characteristics in the Ti-Ni-Hf composite

The Ti-Ni-Hf shape memory alloy was the most potential high temperature shape memory alloy due to the perfect combination of the higher transformation temperatures, larger work output, excellent damping capacity and lower costs. However, the simultaneous occurrence of the formation of (001) compound twin and the slip of a/2 on the (001) plane during deformation resulted in the poor recoverable strain (~4%) owing to its inherent lower matrix strength, further limiting their extensive applications. In the present study, we designed a quasi-continuous network structure formed by the in-situ reinforcements in the Ti-Ni-Hf composite, which can be achieved by incorporating the lower energy milling and vacuum hot-pressed sintering of the Ti-Ni-Hf alloy powders and ceramic particles. The Ti-Ni-Hf composite reinforced by multiple in-situ reinforcements with a quasi-continuous network structure not only had the relatively martensitic transformation temperature, but also exhibited good mechanical properties and strain recovery characteristics. Meanwhile, the mechanisms for the effects of in-situ reinforcement with quasi-continuous network structure on the martensitic transformation, microstructure and interface structure, mechanical properties and strain recovery characteristics were discussed. The present study would provide new ideas and new methods to design and develop new type high temperature shape memory alloy with excellent strain recovery characteristics.