Effect of Heat Treatment Holding Time on Microstructure and Tensile Properties of Ti55511 Alloy

The effect of holding time of double annealing process on the microstructure and mechanical properties of Ti-5Al-5Mo-5V-1Cr-1Fe (Ti55511) alloy was investigated. Results reveal that the shape and size of the primary alpha (alpha p) phase are predominantly influenced by the holding time at the first stage. With the prolongation of holding time, the long strip of alpha p is transformed into a short rod due to the terminal migration mechanism, leading to the broadening growth, and the growth of alpha p slows down when the holding time is over 2 h. The volume fraction of alpha p is mainly affected by the holding time of the second stage: with the prolongation of holding time, the volume fraction of alpha p is increased, which is accompanied by the precipitation of the secondary alpha (alpha s). The mechanical properties of Ti55511 alloy are influenced by both alpha p and alpha s. Tensile results indicate that the optimal holding time of double annealing is 1-4 h for the first stage and 0.5-2 h for the second stage.