Influence of Zr Content on Microstructure and Corrosion Behavior of As-Cast Zr-Modified Ti6Al7Nb Alloy for Biomedical Applications

Ti6Al7Nb alloy is widely used as implant material at present. In order to further enhance its service performance, in this study, we systematically studied the mechanical properties and corrosion properties of as-cast alloy Zr-modified Ti6Al7Nb in SBF solution. The chemical composition of the alloy is Ti6Al7NbχZr (χ = 0, 5, 10, 15 and 20 wt.%) and abbreviated as TANχZ. The phase composition and microstructure are characterized by x-ray diffraction, optical microscopy, scanning electron microscopy and transmission electron microscopy. The results reveal that the β stabilization ability of the alloy is enhanced with the increase of Zr content. The presence of Zr renders a synergistic influence of grain refinement strengthening and solid-solution strengthening. Compared with Ti6Al7Nb alloy, TANχZ alloys deliver higher yield strength and lower modulus of elasticity due to appearance of β phase. The compressive yield strength increased from 691 to 910 MPa. Among them, the TAN20Z alloy has a low elastic modulus of nearly 50 Gpa and an elastic deformation range of up to 2%. Moreover, electrochemical tests are carried out to assess the corrosion resistance in biological environments by immersing two sets of samples in the simulated body fluid (SBF) solution for 3 h and 15 days. After a period of service, the corrosion rates of TAN10Z alloy and TAN20Z alloy are 0.003316963 and 0.002707252 μm year−1, respectively, much lower than the corrosion rates before immersion 0.145459347 and 0.024861533 μm year−1. These results demonstrate that the introduction of Zr significantly improves the mechanical properties and corrosion behavior of TANχZ alloys.