Effect of Mo on the Microstructure and Superelasticity of Ti-Ni-Cu Shape Memory Alloys

Abstract

In this paper, the microstructure and superelasticity of Ti(50−x)Ni44Cu6Mox (x = 0-2.5) alloys were studied. The main phase in Ti(50−x)Ni44Cu6Mox alloys at room temperature is B2 austenite. The martensite transformation finish temperatures of the 0Mo and 0.2Mo samples are approximately − 34.2 and − 45.4 °C, respectively, while the transformation temperature cannot be detected above − 50 °C for the samples with Mo contents greater than 0.2%. The content of Mo has little effect on the compressive strength of the Ti(50−x)Ni44Cu6Mox alloy, but the fracture strain decreases with increasing Mo content. The 0.6Mo sample shows elastic deformation characteristics and has the lowest fracture strain due to the precipitation of Ni-rich compounds. Cyclic compression tests with an increased and constant prestrain were adopted to study the superelasticity properties of the alloys. The residual stress can increase approximately 5-6% after 5 cycles when the prestrain increases from 2 to 10%, while the residual strain drops approximately 2-3% after 20 cycles when the prestrain is constant at 6%. In both experiments, the results show that the recoverable strain can be generally improved by substituting Mo for Ti in Ti(50−x)Ni44Cu6Mox alloys.