Martensitic transformation and mechanical properties of Ti-Ni-Hf high temperature shape memory alloy with network structure second particles

Abstract

The redistribution of the second phases in Ti-Ni-Hf alloy was achieved by the hot-pressed sintering of the rapid solidified alloy powders. The second phases distributed mainly at the surface of the original alloy powder other than the grain boundaries, forming a network structure. The second phase was (Ti,Hf)2Ni phase, when the sintering temperatures were not more than 1100 °C. The (Ti,Hf)2Ni and Hf2Ni phases coexisted at the sintering temperature of 1150 °C. Such a change of the second phases in type and distribution led to the variation of the martensitic transformation temperatures. The martensitic transformation temperatures increased slightly when the sintering temperatures increased from 1000 °C to 1100 °C and then decreased when the sintering temperature was 1150 °C.The sintered Ti-Ni-Hf alloys with a network structure formed by the second phases showed the higher compressive strength and the larger recoverable strain, without significantly sacrificing the compressive strain.