Hot torsion behavior of SP-700 near beta titanium alloy in single and dual phase regions

Abstract

Abstract Hot deformation behavior of the SP-700 alloy is studied through continuous and interrupted hot torsion testing carried out at 850 and 1 000 °C at different pass-strains and inter-pass times. The flow curves of SP-700 alloy showed the discontinuous yield stress, which is followed by the steady state region. The dominant mechanism of softening in hot deformation at 1 000 °C was dynamic recrystallization (DRX), whereas at 850 °C serration and tanglement of the grain boundaries were observed. Nevertheless, the microstructure of the sample twisted at 850 °C indicated the occurrence of DRX and the formation of fine grains in the vicinity of grain boundaries and triple points by the bulging mechanism. With an increase in the pass-strain of interrupted torsion at 1 000 °C, due to the increase in driving force for nucleation and growth of new grains, the kinetics of static restoration increased. However, due to the completion of DRX, the kinetics rate of static restoration at steady state strain (∊ s) was lower than that of the former state. The β → α phase transformation at 850 °C was found to be another factor contributing in fractional softening.