Hot deformation behaviour and microstructural evolution of biomedical Ti-13Nb-13Zr alloy in high strain rate range

Abstract

The deformation behaviour and microstructural evolution of biomedical Ti-13Nb-13Zr alloy are investigated at strain rates of 1×103s−1, 2×103s−1 and 3×103s−1 and temperatures of 25°C, 650°C and 800°C using a compressive split-Hopkinson pressure bar (SHPB) system. The results show that the flow stress, strain rate sensitivity and temperature sensitivity increase with increasing strain rate or decreasing temperature. In addition, adiabatic shearing occurs in the specimens deformed at 25°C and 650°C under the maximum strain rate of 3×103s−1. For the specimen deformed at 25°C, the adiabatic shear band results in catastrophic failure. The microstructural observations reveal that single β phase is formed under the highest temperature of 800°C. The volume fraction of α' martensite and the dislocation density increase, but the grain size decreases, as the temperature is reduced or the strain rate increased. The average thickness of the α' laths reduces as the strain rate and temperature increase. The interaction between the grain size, dislocation density and α'martensite volume fraction leads to a significant strengthening effect. The higher flow stress caused by this strengthening effect can be estimated using an empirical model of the form σ=σo+KD−1/2+K'ρ1/2+Ωξ, where K, K'and Ω are equal to 69.82MPaμm1/2, 6.62 MPaμm and 105.4MPa, respectively. The average error in the flow stress estimates is found to be just 2.04% for the temperature and strain rate conditions considered in the present study. Overall, the results presented in this study provide a useful insight into the combined effects of strain rate and temperature on the hot working behaviour and deformability of Ti-13Nb-13Zr alloy. In general, the results confirm that Ti-13Nb-13Zr alloy is well suited to the fabrication of orthopaedic implant devices and structural components in the biomedical and engineering fields, respectively.