Stress-Induced Martensitic Transformation and Microstructure of a Ti_(36)Ni_(49)Hf_(15) High-Temperature Shape-Memory Alloy

摘要

The stress-induced martensitic transformation behavior and the microstructure of stress-induced martensite (SIM) in a Ti_(36)Ni_(49)Hf_(15) high temperature shape memory alloy (SMA) have been investigated using tensile tests and transmission electron microscopy (TEM) in this paper. It shows that, compared with TiNi SMAs, there is no stress plateau in the stress-strain (S-S) curve as the TiNiHf alloy deformed in austenite. The martensitic transformation enthalpy is calculated to be -106.84cal/mol. The martensite variants mainly show preferential oriented morphologies for the TiNiHf alloy deformed to 8% at 523k. The substructure of SIM and deformed SIM in the present alloy is (001) compound twin. Martensite variants are (011) type I twin related. Further increasing the deformation temperature and strain, the preferential oriented SIMs gradually develop to martensite variants with variant-crashed / variant-intersected morphologies. The inexistence of stress plateau in the S-S curve of the TiNiHf alloy may mainly result from the dislocation slip during stress-induced martensitic transformation.