Precipitation and evolution behaviors of grain boundary α and α side plates for ultra-high strength titanium alloy during continuous cooling

In this paper, precipitation behavior and evolution mechanism of grain boundary α (αGB) and α side plates (αSP) of ultra-high strength titanium alloy are investigated. Precipitation of αGB can change original morphology of β grain boundary into irregular shapes, and it is much more obvious at slower cooling rate. The λ, which denotes the minimum value of misorientations between 12 α variants of βnBOR and αGB, is introduced to quantitatively evaluate morphology of αGB. The β phase that maintains Burgers orientation relationship (BOR) with αGB is labeled as βBOR, conversely, it is labeled as βnBOR. The deformation degree of αGB increases with the increasing λ. However, the λ is not the only factor that determines morphology of αGB, and it is also related to the angle between habit plane and grain boundary plane. Orientation of αGB is affected by β phase on both sides. The αGB maintains BOR with βBOR and the s-BOR with βnBOR. The s-BOR is defined as (0 0 0 1) plane of αGB is not parallel to (1 1 0) plane of βnBOR, but one of 〈1 1 –2 0〉 directions of αGB is parallel or close to one of βnBOR's 〈1 1 1〉 directions.