Shape Memory Behaviour of Ti-Nb-Zr Alloy After Slow Cooling Rate

Ti-Nb-Zr shape memory alloys (SMAs) have been commonly characterized by means of thermal cyclic testing rather than differential scanning calorimetry (DSC) analysis in the past decade, since the elastic strain energies of these SMAs were too small to be detected. In this study, the shape memory behaviour of Ti-Nb-Zr alloy was investigated using the DSC analysis and X-ray diffraction (XRD) measurement. The alloy ingots were prepared using an arc melting technique followed by cold rolling to the final dimension of ~1mm in thickness. The alloys were then annealed at 1023K for 15minutes, followed by either furnace cooling or ice water quenching. Typical martensitic lamellar structure in the β matrix was observed. XRD measurement revealed the presence of the martensite phase. Forward and reverse martensitic transformations were found in the annealed specimen subjected to furnace cooling. However, only a small amount of ω phase existed in the annealed specimen subjected to ice water quenching, and no obvious reverse martensitic transformation was found upon cooling. This indicates that this alloy behava differently when compare with Nitinol, which usually give more promising shape memory behaviour upon fast cooling. Cooling rate was found a crucial factor in controlling the microstructure, thus the thermoelastic properties of the Ti-Nb-Zr SMA.