Microstructure and phase transition characteristics of NiTi shape memory alloy

Abstract

Shape memory alloy (SMA) with shape memory effect and superelasticity has had an increasing interest for researchers of mechanics of materials in recent decades. With the deepening of theoretical research, the applications of SMA have also made considerable progress. SMA has a unique solid phase transformation characteristic that is thermoelastic martensitic transformation. The high temperature phase of SMA is austenite, while the low temperature phase of SMA is martensite. Because of the biocompatibility and the corrosion resistance, NiTi shape memory alloy has been widely used in biomedical and aerospace. However, the NiTi binary alloy can only be applied to the ambient temperature, because the phase transformation temperature is lower than 100 centigrade. In order to apply the NiTi based shape memory alloy in the wider field, it is necessary to control the phase transformation temperature, thermal hysteresis latent heat of phase change and other phase transformation behavior and mechanical property effectively and accurately. Thus, it is important to add a third or fourth element to NiTi alloy to form a new type of NiTi based shape memory alloy. The results show that NiTi alloy contains many precipitates such as NiTi2, Ni3Ti2, Ni4Ti3. Adding the third or even the fourth element to the NiTi binary alloy can effectively adjust the phase transition and related mechanical properties of NiTi alloy. In this paper, the research progress of NiTi binary alloys is summarized, the microstructure, types and structures of properties, types and properties of phase transitions of NiTi alloys are introduced respectively, the problems faced by NiTi alloys are analyzed and their prospects are prospected, so as to provide reference for the development of shape memory alloys with better properties.