Research on the synergistic improvement mechanism of plasticity and superelasticity of the Ni50.3Ti29.7Hf20 high temperature shape memory alloy by rolling and electric pulse coupling treatment

In order to improve the mechanical property and functional stability of high temperature shape memory alloys, a “rolling and electric pulse” coupling treatment was proposed in the Ni 50.3 Ti 29.7 Hf 20 alloy. The mechanism of synergistic improvement of both plasticity and superelasticity was investigated via DSC, TEM, and performance testing, which was induced by both thermal and athermal effects of the pulse current under the conditions of twin martensite and dislocation proliferation. The results indicate that “rolling and electric pulse” coupling treatment is an effective method to simultaneously improve the plasticity and superelasticity of the Ni 50.3 Ti 29.7 Hf 20 alloy. The optimal parameter is identified as “50% hot-rolled deformation combined with an instantaneous process of 50μs/250Hz”, and thus accompanied by the most effective temperature of 550 °C. Compared to the as-cast state of the Ni 50.3 Ti 29.7 Hf 20 alloy, the phase transformation sequence (A↔M) and phase transformation temperature ( A f > 200 °C) are remained unchanged after “rolling and electric pulse” coupling treatment. The plasticity is increased by 50%, The plasticity is increased by 50% without an obvious strength reduction, and the functional stability is significantly improved in the Ni 50.3 Ti 29.7 Hf 20 alloy. The synergistic enhancement of both plasticity and superelasticity is primarily attributed to the targeted effects of the pulse current on the defects induced in the hot-rolled Ni 50.3 Ti 29.7 Hf 20 alloy, as well as the homogenization effects on the microstructure. This research will have an important theoretical significance and application value to promote the development of the high temperature shape memory alloys with excellent performance.