Mechanisms of grain boundary α precipitation in the metastable β-titanium Ti-5Al-5Mo-5V-3Cr

In this study, we investigated the early nucleation and growth of grain boundary alpha during the aging heat treatment of Ti-5553. Through a correlative approach using scanning electron microscopy, electron backscatter diffraction, transmission Kikuchi diffraction, transmission electron microscopy, and atom probe tomography, high-angle beta-grain boundaries were investigated in detail to understand the evolution of the precipitation of grain boundary alpha through nucleation and subsequent growth. It is found that at grain boundaries there is a pronounced nucleation of alpha precipitates with similar orientations. Growth of these similarly orientated alpha precipitates, in the later stages, leads to their agglomeration and the formation of grain boundary alpha. This investigation provides insights into the formation of grain boundary alpha in its early stages of nucleation and growth.