Investigation of Dynamic and Static Restoration in Hot Deformation of SP-700 Titanium Alloy

In order to investigation of dynamic and static restoration of SP-700 alloy, in this study continuous and interrupted hot torsion tests carried out at 850 and 1000ºC at different pass-strains and inter-pass times. The dominant mechanism in hot deformation at 1000°C is dynamic recrystallization (DRX) and consequently the entire microstructure comprises equiaxed grains, whereas at 850°C serration and tanglement of the grain boundaries were observed. Nevertheless, the microstructure of sample twisted at 850°C, indicates the occurrence of DRX and the formation of very fine grains. The mechanism of the formation of recrystallized grains in the vicinity of grain boundaries and triple points is bulging. With an increase in pass-strain (ε=0.5) at 1000°C, due to the increase in driving force for nucleation and growth of new grains, the kinetics of static restoration increases. In fact, at 850°C, in addition to static restoration there is another factor contributing in fractional softening which is β to α phase transformation.