Effects of solution treatment and aging on the microstructure, mechanical properties, and corrosion resistance of a β type Ti–Ta–Hf–Zr alloy

Abstract

Titanium and some of its alloys have become increasingly important for biomedical materials due to their high specific strength, good corrosion resistance, and excellent biocompatibility compared to the biomedical stainless steels and cobalt–chromium based alloys. In this study, a β type TTHZ alloy (Ti–40Ta–22Hf–11.7Zr) was prepared with the cold-crucible levitation technique. The corrosion behavior and the effects of solution treatment (ST) and aging on the microstructures and mechanical properties of the TTHZ alloy were investigated using electrochemical analysis, XPS (X-ray photoelectron spectroscopy), OM (optical microscopy), XRD (X-ray diffractometry), TEM (transmission electron microscopy) and compressive testing. The results indicate that the as-cast alloy exhibited a β + ω_ath microstructure, which transformed into a single β phase after ST at 900 °C for 1 h. The β phase further transformed into β + α′′, β + α′′ + α, and β + α + ω_iso after aging for 15 min, 1.5 h, 12 h and 24 h, respectively. The different phases of the TTHZ alloy showed significantly different mechanical properties and corrosion behavior. The solution-treated TTHZ alloy exhibited a compressive yield strength of approximately 1018 MPa and an excellent compressive strain as no fracturing was observed; and the compression tests were stopped at a compressive strain of ∼70%. The TTHZ alloy after solution treatment plus aging exhibited an increase in the compressive yield strength with a decreased compressive strain. The solution-treated TTHZ alloy exhibited a single β phase with the highest corrosion resistance, compared to the as-cast and solution-treated alloy, followed by aging samples. The open-circuit potential (OCP) analysis indicates that the corrosion resistance of the as-cast TTHZ alloy was superior to those of both CP-Ti and Ti6Al4V.