A Group of Ni-free Super-elastic beta Ti Alloys

Abstract: NiTi alloys have been largely used in medical applications benefited from their large super-elastic properties. However, Ni-related allergic reactions have been continuously reported in some patients, which keep pushing researches on Ni-free alternatives. To achieve this goal, a group of Ni-free Ti-Hf based beta alloys were recently developed. The mechanical properties and deformation behavior were investigated by cyclic tensile testing and in-situ synchrotron X-ray diffraction. Due to the reversible stress-induced martensite phase transformation, this material was able to fully recover ~4% deformation strain after proper heat treatment.  A maximum recoverable strain of above 5% can be achieved after 6% deformation strain. In addition, these properties are stable due to the lack of room temperature aging effect, implying that they might be good candidates for medical applications that require large strain recovery and a Ni-free environment.