Precipitation Behavior and Microstructural Evolution of α Phase during Hot Deformation in a Novel β-Air-Cooled Metastable β-Type Ti-B12 Alloy

The precipitation behavior and microstructural evolution of α phase in a novel metastable β-type Ti alloy, Ti-10Mo-6Zr-4Sn-3Nb (wt.%), during isothermal compression are investigated in this study through the use of SEM (scanning electron microscope), TEM (transmission electron microscope) (HRTEM) (high-resolution transmission electron microscopy) and EBSD techniques. The results show that some finer α precipitates are randomly distributed within the β matrix during hot deformation. The morphological characteristics of α precipitates are distinctly different from those of α precipitates during the same solution-plus-aging treatment. The volume fraction of α precipitate gradually increases with increased true strain. A large proportion of precipitated α phases are prone to be precipitated at HAGBs (high-angle grain boundaries) and LAGBs (low-angle grain boundaries) during isothermal deformation. On the contrary, only a small amount of spherical α phases is precipitated within the β grain. The crystallographic orientation relationships for most spherical α precipitates formed at LAGBs and within the β grains are similar, whereas the crystallographic orientation relationships for α precipitates at grain boundaries are significantly different. The precipitation behavior of α phase in the Ti-B12 alloy during hot compression is considerably influenced by the density of dislocations