Microstructural evolution and mechanisms for improved performance of powder metallurgy Ti-6Al-4V alloys after thermal deformation and heat treatment

Ti-6Al-4V alloy prepared through powder metallurgy forging and heat treatment has been investigated to explore the relationship between microstructure evolution and mechanical properties. This work indicates that the spheroidization process following forging is primarily driven by local grain rotation, triggered by dislocation accumulation, which is significantly correlated with enhanced ductility. In contrast, heat treatment is mainly facilitated by the synergistic effect of element concentration gradients, resulting in a notable ultimate tensile strength of 1201 MPa with an elongation of 12.3 %. The improvements are due to the combined effects of interface strengthening at the αs interfaces, the formation of hexagonal dislocations in the αp, and the synergistic plastic deformation between the αp and αs. Additionally, the primary slip system is identified as the pyramidal slip in the alloys both before and after heat treatment, due to a decrease in the critical resolved shear stress and a reduced c/a ratio from element redistribution, respectively. These findings offer valuable insights into the spheroidization mechanism of Ti-6Al-4V alloys and present new perspectives for designing titanium alloys with both high strength and excellent ductility. •Ti-6Al-4V shows spheroidization after forging, increasing elongation.•Heat treatment αp spheroidization relies on elemental gradient synergy.•Pyramidal slip activation is linked to critical resolved shear stress and c/a ratio.•Calculations show αs enhances interface strengthening.•Synergistic deformation of αp and αs with twinning, enhances elongation.