Effect of ageing on internal friction and elastic modulus of Ti–Nb alloys

This study aims to investigate the changes in internal friction and Youngʹs modulus during ageing phase transformations in titanium–niobium binary alloys. Four types of alloys, which had niobium concentrations of 25, 30, 35, and 40 mass%, were used. These alloys were solution-treated at 1223 K, and aged at 423, 573, and 723 K. Although the highest Youngʹs modulus of the quenched specimens was observed in the α″ + β duplex structure of T30N and not the α″ martensite structure of T25N, it decreased with the amount of α″ martensite in other alloys. The internal friction of the quenched specimen decreased as the amount of the β phase increased. The internal friction increased, but Youngʹs modulus decreased during the processes of α″ → β reverse transformation and α precipitation during the ageing treatments. On the other hand, the internal friction decreased, but Youngʹs modulus increased during the process of aged ω precipitation. In particular, the decreased internal friction of the α″ martensite structure of Ti–25Nb alloys aged at 723 K and the changes in both the internal friction and Youngʹs modulus during the process of aged ω precipitation of the α″ + β duplex structure were remarkable.