Exploration of the static softening behavior and dislocation density evolution of TA15 titanium alloy during double-pass hot compression deformation

The static softening behavior and dislocation density evolution of TA15 titanium alloy during double-pass hot deformation were investigated under the deformation temperatures (910 °C–970 °C) and holding time (0s–2200s). The microstructure evolution of primary α phase was observed by optical micrograph (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The evolution of dislocation density was investigated via X-ray diffraction (XRD) and W–H model. The results showed that the globularization behavior of primary α phase is emerged during the inter-pass of double-pass hot deformation. The globularization process is promoted by the extension of the inter-pass holding time and the increase of the deformation temperature. The groove of primary α phase is preferentially generated when the inter-pass holding time within 1000s. Subsequently, that groove of primary α phase is separated and then those α phases are dissolved when the holding time over 1000s, leading to the fraction of α phase reduction. Compared with deformation temperature of 910 °C and 940 °C, all of the primary α phases are completely separated after 1000s of the inter-pass holding time under 970 °C. Additionally, through the analysis of various crystal surface of α phase, the dislocation density in the inter-pass gradually decreases with the holding time and deformation temperature increasing.