A complementary precipitated mechanism of grain boundary α phases in metastable β titanium alloy

Abstract

In titanium alloys, the grain boundary α(α_GB) phase constitutes a critical microstructural feature whose characteristics affect the mechanical properties of the alloys. However, current understanding of the α_GB precipitation process remains incomplete, posing significant challenges in precisely controlling its morphology. In this study, we systematically investigated the morphological evolution of α_GB during distinct precipitation stages and proposed a grain boundary curvature mechanism. During progressive step cooling, α_GB phases initially nucleate at multiple sites along grain boundaries. Subsequently, α_GB phases exhibit preferential growth toward one adjacent grain, thereby inducing localized curvature of the grain boundaries. The final stage involves coarsening and coalescence of α_GB phases, accompanied by the precipitation of grain boundary Widmanstätte α (α_WGB) colony at the α_GB particle intersections or the α_GB phase endpoints. This finding provides a more comprehensive framework for interpreting α_GB precipitation sequence, but also a theoretical guidance for microstructure tailored strategies in advanced titanium alloys.