Micro-texture weakening in bimodal Ti60 alloy via two-step sub-transus thermomechanical processing: Mechanistic insights into the regulation of crystallographic orientation homogenization

Micro-texture regions (MTRs), arising from the combined influences of prior β orientations and secondary-α (α s ) variant selection, are pervasive in forged titanium alloy disks and critically degrade deformation uniformity and mechanical reliability. Their resistance to orientation homogenization renders MTR weakening a key challenge for fabricating high-performance titanium alloys. In this study, Ti60 alloy with pronounced MTRs was processed through various sub-transus thermomechanical processing routes to clarify the underlying mechanisms and identify effective weakening strategies. Multiscale characterization and improved quantitative evaluations of MTR intensity and Burgers orientation relationship (BOR) deviation were employed to correlate microstructure evolution with crystallographic orientation regulation. Results demonstrate that coordinated regulation of primary-α (α p ) recrystallization, β-grain growth, and α s precipitation governs MTR weakening. Direct heat treatment preserved concentrated α p orientations and BOR, sustaining stable MTRs. Compression near the sub-transus temperature significantly increased BOR deviation and mitigated variant selection but generated deformation texture due to orientation inheritance. In contrast, low-temperature dual-phase compression followed by high-temperature heat treatment achieved the most effective MTR weakening (0.732 → 0.141) while avoiding deformation texture formation. Low-temperature compression facilitates α p orientation dispersion and supplies the driving force for static recrystallization and phase transformation, enabling the formation of β grains and α s precipitates with more uniform orientations. MTRs with c-axes perpendicular to the compression direction exhibit exceptional stability in thermomechanical processing due to preferential prismatic slip. These findings establish a comprehensive mechanistic framework for MTR weakening and provide processing guidance for orientation homogenization in advanced disk-grade titanium alloys.