Abstract
Morphology of secondary grain boundary α phase (αGB) has great influence on grain boundary Widmanst?tten α phase (αWGB) cluster and further fracture toughness and ductility of the titanium alloys. In this paper, the bifurcation behavior and morphology of secondary αGB in TC18 titanium alloy were investigated through high and low temperature two-step heat treat experiment (910 °C/30 min→800 °C/45 min/WQ) combined with a three-dimensional reconstruction experiment. It was found that αGB showed flat, equiaxed, zig-zag morphologies, and αGB 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, β/β grain boundary or the triple junction (TJ) of β grain boundary. The bifurcation behavior of α phase at TJ is related to its original morphology. Bi-direction bifurcation occurs mostly in the flat αGB, but is not observed in the zig-zag αGB. The present results provide new information on αGB of TC18 titanium alloy.
NSTL
Elsevier