The Elevated-Temperature Strength Enhancement of a Low-Cost β Titanium Alloy Through Thermomechanically-Induced Phase Transformation

Abstract

The effects of temperature and thermomechanical loading on the tensile strength and hardness were studied for a rolled, low-cost metastable β titanium alloy, Ti-13Cr-1Fe-3Al (wt.%). Tensile tests were performed at temperatures between room temperature (RT) and 410°C. The results indicated that the ultimate tensile strength (UTS) decreased with increasing temperatures up to 300°C. However, the UTS was 1400 MPa at 410°C, which was approximately 150% higher than the RT UTS. It is believed that the formation of nanoscale ω and α precipitates, identified using transmission electron microscopy, hindered the dislocation motion, which resulted in the exceptionally high UTS at 410°C. However, ductility was maintained, as the elongation-to-failure (ef) was ~ 10% at 410°C. Dynamic mechanical analysis suggested that phase transformations occurred between 370°C–475°C. To evaluate the effect of the phase transformations on the hardness, the as-received material was heat treated at 400°C, 450°C, and 500°C for 2 h, which resulted in hardness values of approximately 340 Hv, 380 Hv, and 470 Hv, respectively. However, the greatest hardness value (500 Hv) was exhibited by the as-received material after it was tensile tested at 410°C. This suggested that both temperature and loading history affected the phase transformations. As all the samples exhibited a ductile fracture mode, this work indicates that it is possible to maintain both high strength and adequate ef for Ti-13Cr-1Fe-3Al (wt.%).