Study on bifurcation behavior and morphology of the secondary grain boundary a phase in TC18 titanium alloy

Morphology of secondary grain boundary alpha phase (alpha(GB)) has great influence on grain boundary Widmanstatten alpha phase (alpha(WGB)) cluster and further fracture toughness and ductility of the titanium alloys. In this paper, the bifurcation behavior and morphology of secondary alpha(GB) in TC18 titanium alloy were investigated through high and low temperature two-step heat treat experiment (910 degrees C/30 min -> 800 degrees C/45 min/WQ) combined with a three-dimensional reconstruction experiment. It was found that alpha(GB) showed flat, equiaxed, zig-zag morphologies, and alpha(GB) bifurcated to reduce the energy of the system and maintained the stability of structure by interfacial instability nucleation. There exist two types of bifurcation behaviors, bi-direction bifurcation and tri-direction one. The significant difference between them is nucleation positions, beta/beta grain boundary or the triple junction (TJ) of beta grain boundary. The bifurcation behavior of alpha phase at TJ is related to its original morphology. Bi-direction bifurcation occurs mostly in the flat alpha(GB), but is not observed in the zig-zag alpha(GB). The present results provide new information on alpha(GB) of TC18 titanium alloy. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study investigated the bifurcation behavior and morphology of secondary alpha(GB) in TC18 titanium alloy. Two types of bifurcation behaviors, bi-direction bifurcation and tri-direction bifurcation, were observed. Bi-direction bifurcation mainly occurred in flat alpha(GB), while it was not observed in zig-zag alpha(GB).