Origin of morphological variation of grain boundary precipitates in titanium alloys

Abstract

Morphological variations of grain boundary (GB) allotriomorphs and widmanstatten sideplates (WS) of α precipitate in a β titanium alloy, have been systematically investigated by combining three-dimensional (3D) phase-field simulations, 3D experimental characterization and crystallographic orientation analysis. The inclination angle, θ, between the habit plane of the GBα and the hosting GB plane is found to dictate the morphologies of GB precipitates. For the first time, three distinct regimes of α morphology at a β GB, separated by two critical angles (θc1, θc2) are observed: θ≤θc1, GBα alone decorates the GB as a continuous layer; θc1<θ≤θc2, α precipitate appears as a mixture of GBα and a WS emanating from it; θ>θc2, WS alone grows directly from bare β GBs. The dramatic morphological variation owes its origin to the dynamic interplay between the spreading along GBP and the intragranular growth of the GB precipitate, and its dependence on θ.