The Influence of Thermomechanical Processing on the Microstructure of Metastable Beta-Ti Alloys

This paper describes the effect of working history on the subsequent microstructure and hardness variations during aging of Ti-11.5Mo-6Zr-4.5Sn. Two different thermomechanical processing schemes were used to vary the percent recrystallization and dislocation density of the metastable bcc phase. These samples were then aged at different temperatures for varying times and the increases in hardness were monitored using Vicker's hardness measurements. Significant differences in hardening response were observed depending on whether the working of the material was completed well below or at the beta-transus. Transmission electron microscopy was used to correlate the age hardening response with microstructure. Significant differences in primary alpha distribution were detected in the as-hot-worked materials processed by the two different schemes and these differences helped to account for the variations in age hardening response. In both materials, it was shown that sufficient heterogeneous nucleation sites in the form of dislocations were present to promote direct nucleation of alpha-phase, thereby eliminating the embrittling omega-phase. (Author) Pub. in Proceedings of International Conference on Strength of Metals and Alloys (4th) held on Aug 76 at Nancy (France). Prepared in cooperation with Colt Industries, Pittsburgh, PA. Crucible Materials Research Center.