Microstructure and mechanical properties evolution during thermomechanical processing of a Ti–Nb–Zr–Ta–Sn–Fe alloy

Abstract

During the last decades, Titanium-based alloys have shown a suitable combination of strength, ductility, corrosion and biocompatibility properties, that marks them as suitable implant materials for biomedical applications. In this study, a Ti–30Nb–12Zr–5Ta–2Sn-1.25Fe (wt%) alloy was produced by melting in a cold crucible induction in levitation furnace, deformed by cold rolling, with a total deformation degree (thickness reduction) of 50%, in five equal steps, and solution treated at 850 °C, with progressive treatment durations, from 5min to 20min, in 5min increments. The initial microstructure is homogenous, consisting of equiaxed β-Ti phase grains showing an average grain size close to 135 μm. The applied cold deformation induces changes in the microstructure, which shows the presence of deformation bands, twins, dislocation bands and of an increased crystal defects density and residual strain–stress fields. Also, an increase in strength and decrease in ductility properties are noticed due to the strain hardening. The applied solution treatment leads to the regeneration of the microstructure, the obtained microstructure showing homogeneous equiaxed β-Ti phase grains, with an average grain size between 60 μm and 80 μm, depending on the solution treatment duration. Also, a decrease in strength and increase in ductility properties are noticed due to the lowering of the crystal defects density, remanent strain–stress fields and an increase of the average grain size.