Effect of Hf Content on the Microstructure and Superelasticity of Ti49-XNi44Cu6Y1HfX Shape Memory Alloys

Ti-Ni-Cu based shape memory alloy has excellent properties such as small phase transformation hysteresis, large recoverable strain and good thermal stability. The purpose of this work is to systematically investigate the effect of substituting Hf for Ti on the microstructure, phase transformation and superelasticity of Ti49-X Ni44 Cu6 Y1 HfX (X = 0, 2, 6, 10) alloys. The results show that the main microstructure of the alloy at room temperature is B2 austenite and a small amount of compound phase. And one-step martensitic transformation of B2-B19′ occurs during the loading and unloading processes. With the increase of Hf content, the martensitic transformation temperature decreases, the compressive strength and fracture strain of the alloy decrease, and the critical stress of stress-induced martensite increases. In the cycle compression tests with an increased compressive strain of 3%—11%, the alloy exhibits work hardening phenomenon, and the recoverable stress increases with the increase of prestress. The sample of 10%Hf has the largest recoverable strain of 7. 9% when the compressive strain is 11%, and the superelasticity strain is 5. 2%. In the cycle compression tests with a constant compressive strain of 7%, the sample of 10%Hf has good cyclic stability and can be completely recovered. © 2023 Cailiao Daobaoshe/ Materials Review. All rights reserved.