Microstructure evolution of a new near-β titanium alloy: Ti555211 during high-temperature deformation

The isothermal compression testing of Ti555211 titanium alloys was carried out at deformation temperatures from 750 to 950 degrees C in 50 degrees C intervals, with strain rate of 0.001-1.000 s(-1) and height reduction of 20 %-60 %. The effect of processing parameters (deformation temperature, strain rate and deformation degree) on the microstructure evolution and the microstructure variables was investigated. The results show that the content of primary alpha phase decreases with the increase in deformation temperature. The effect of strain rate on microstructure variables of isothermally compressed Ti555211 alloy is mainly dependent on the deformation temperature. The fine second alpha phase partly transforms to beta phase due to the deformation heat effect at the high strain rate. alpha phase becomes globular with temperature increasing and strain rate decreasing. In contrast, alpha phase is refined with temperature decreasing and strain rate increasing. The deformation degree has a little influence on the grain size and the morphology of primary alpha phase, but the effect of deformation degree on the morphology of second alpha phase is significant. The larger deformation degree is in favor of the globularization of lamellar alpha structure.