Dynamic recovery and recrystallization in beta-titanium alloys

Microstructure change during hot deformation was studied in β titanium alloys, Ti-10V-2Fe-3Al and Ti-15V-3Cr-3Sn-3Al. After β solution treatments, isothermal compression was performed at various temperatures in the β single-phase and in the (α+β) two-phase region at initial strain rates between 4.2×10^-1 ∼- 4.2×10^-5 s^-1. When the specimens are deformed in the β single phase region, a recovered structure was formed within β grains although discontinuous dynamic crystallization occurs in the vicinity of β grain boundary. When deformation was performed in the (α+β) two-phase region just below the β transus, discontinuous recrystallization around β grain boundary is suppressed due to the pinning effect by grain boundary a precipitate, resulting in a mostly recovered structure. Contrarily, when the specimen is deformed at the temperature where a large amount of α precipitates, dynamic continuous recrystallization occurs uniformly in β matrix, resulting in the formation of (α+β) microduplex structures containing high-angle β boundaries. The size of recrystallized β grain decreases as strain rate increases or deformed temperature is lowered in a good correlation with Zener-Hollomon parameter.