Thermomechanical processing of near-β Ti–5Al–5Mo–5V–1Cr–1Fe alloys: Effect of deformation reduction on microstructures and mechanical properties

Abstract

Deformation reduction, a thermomechanical processing parameter, has a significant impact on the microstructure and mechanical properties of titanium alloys. In this study, the effect of deformation reduction on the microstructures, textures, and mechanical properties of near-β Ti–5Al–5Mo–5V–1Cr–1Fe (Ti55511) alloys in the β-region is investigated by conducting several forging experiments. The results show that deformation reduction has a significant impact on the microstructures of prior-β grains. As the deformation reduction increases from 20% to 80%, the shape of prior-β grains of Ti55511 gradually transform from equiaxed to elongated. Once the deformation reduction reaches 60% or even higher, the dynamic recrystallization is stimulated with the formation of a strong <100> texture along the forging direction. In addition, αβ-solution-treated and aged (STA) heat treatment is performed to tailor the microstructure of the as-forged Ti55511 alloys, and a typical basket-weave microstructure is obtained. The heat treatment results reveal a negligible relationship between the precipitation and deformation reduction of the basket-weave microstructure during the STA process. Tensile and fracture toughness tests are performed on the Ti55511 alloys with different deformation reductions. The results indicate that the samples with deformation reductions of 20% and 40% exhibit the absence of mechanical anisotropy owing to the equiaxed prior-β grains. For the specimens with 60% and 80% deformation reductions, the combination of strong texture and pancake-shaped prior-β grains leads to strong anisotropies in both tensile and fracture toughness performances. In this study, a relationship is established to reveal the influence of deformation reduction on the microstructure and mechanical properties of Ti55511 alloys during the forging process.