Microstructures and shape memory effect of binary Ti-Zr alloys

In recent years, many researchers have focused on the novel Ti-based alloys due to the good biocompatibility, excellent corrosion resistance, low elastic modulus, high phase transformation temperature, etc. Microstructures, phase transformations, mechanical properties and shape memory effect (SME) of Ti_xZr_100-x (x=20, 30, 50, 70, 80) alloys were systematically investigated by X-ray diffraction (XRD), optical microscopy (OM), transmission electron microscopy (TEM), differential scanning calorimetry (DSC) and compressive stress-train measurements. The results showed that the Ti-Zr alloy was a kind of high temperature shape memory alloy composed of a single hcp-α' twin martensite phase at room temperature. The lattice parameters and unit-cell volume of the Ti-Zr alloy increased with Zr content increasing. The alloys displayed a reversible phase transformation between the hcp martensite and β parent phases. The martensitic phase transformation temperature decreased with Zr content increasing and reached the minimum of about 520℃ when Zr content was equal to 50%. The yield strength of Ti-Zr alloy increased with Zr content increasing, to the maximum of 955 MPa at the composition of 50% Zr, and then decreased with Zr content increasing. All of the Ti-Zr alloys showed shape memory effect and the maximum value of SME was 1.7% as displayed in Ti₇₀Zr₃₀ alloy.