Origin of morphological variation of grain boundary precipitates in titanium alloys

Morphological variations of grain boundary (GB) allotriomorphs and widmanstatten sideplates (WS) of alpha pre-cipitate in a beta titanium alloy, have been systematically investigated by combining three-dimensional (3D) phase-field simulations, 3D experimental characterization and crystallographic orientation analysis. The inclination angle, theta, between the habit plane of the GB alpha and the hosting GB plane is found to dictate the morphologies of GB precipitates. For the first time, three distinct regimes of alpha morphology at a beta GB, separated by two critical angles (theta(1)(c) , theta(2)(c)) are observed: theta <= theta(1)(c), GB alpha alone decorates the GB as a continuous layer; theta 1c < theta <= theta(2)(c), alpha precipitate appears as a mixture of GB alpha and a WS emanating from it; theta > theta(2)(c), WS alone grows directly from bare beta 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 theta.

Automated summary

This study systematically investigates the morphological variations of grain boundary precipitates in a beta titanium alloy, revealing three distinct regimes of alpha morphology at a beta GB separated by critical angles, which are determined by the inclination angle between the habit plane of the GB alpha and the hosting GB plane.