Effect of Deformation Temperature, Strain Rate, and Strain on the Microstructure Evolution of Ti-17 Alloy

This study investigates the effect of deformation temperature, strain rate, and strain on the deformation behavior above and below the beta (β) transus temperature (T_β), as well as the alpha (α) + β microstructure evolution, in Ti-17 alloy during deformation and subsequent cooling to room temperature. Dynamic recovery is the dominant restoration mechanism of the β matrix during hot deformation above and below the T_β, which leads to the formation of subgrain structure under applied conditions. During deformation at temperatures less than the T_β, the α phase precipitates at β grain boundaries initially in a globular or film shape (GB_α), followed by the formation of Widmanstätten α (W_α) plates from the GB_α and inside the β grains. The α precipitation kinetics is accelerated by increasing the deformation strain during deformation at temperatures less than the T_β. Even at temperatures greater than the T_β, deformation is found to induce α-phase precipitation at β boundaries. Further, α-phase precipitation occurs during slow cooling after deformation, whereas greater deformation strain leads to a decrease in the total α-phase fraction because the enrichment of Mo and Cr and the depletion of Al in the β phase by the formation of W_α at higher temperatures stabilizes the β phase and thus suppresses the subsequent β → α transformation during cooling.