Effect of thermomechanical treatment on structure and properties of metastable Ti-25Nb-8Sn alloy

In this work, different thermomechanical treatment conditions were used to improve the mechanical performances of Ti-25Nb-8Sn. During cold rolling treatment (50, 75, and 90 %), as-cast Ti-25Nb-8Sn underwent a stress-induced phase transformation from a single beta phase to a three-phase structure of alpha '' + beta + omega(str). After the subsequent aging treatment, Ti-25Nb-8Sn presents three-phase beta + alpha '' + omega(iso). (at 250 and 400 degrees C, for 30 min) and two-phase beta + alpha (at 600 degrees C, for 30 min). At lower aging temperatures (250 and 400 degrees C), yield strength/modulus (x 1000) ratios of Ti-25Nb-8Sn are dramatically improved with a maximum increase of 143 %, from 9.06 (as-cast) to 16.2-22.0. Under various thermomechanical treatment conditions in this study, the results show that Ti-25Nb-8Sn has excellent yield strength/modulus (x 1000) ratio (similar to 22) and corrosion resistance after 90 % cold rolling and subsequent aging treatment at 250 and 400 degrees C for 30 min.