Temperature-Dependent Phase Separation and Microstructural Evolution in a TiZrNbTaMo Refractory High-Entropy Alloy

The TiZrNbTaMo high-entropy alloy is known to undergo phase separation during annealing at elevated temperatures; however, the relationship between compositional partitioning and crystallographic evolution remains unclear. In this study, the phase separation behavior of arc-melted TiZrNbTaMo alloy was systematically investigated across varying annealing temperatures (1073–1473 K) and times (5–168 h). Microstructural evolution was characterized by X-ray diffraction, backscattered electron imaging, electron probe microanalysis, and electron backscatter diffraction combined with energy-dispersive X-ray spectroscopy to correlate chemical distribution with crystallographic orientation. The as-cast specimen exhibited chemically heterogeneous Zr-rich and Zr-poor regions with an identical crystallographic orientation, reflecting solidification-induced dendritic segregation. During annealing at 1073 and 1273 K, phase separation proceeded through the formation of crystallographically distinct domains, suggesting a nucleation-and-growth-type phase separation pathway accompanied by chemical partitioning. In contrast, prolonged annealing at 1473 K for 168 h induced phase separation into two body-centered cubic phases while maintaining crystallographic continuity within the phase-separated regions. The results demonstrate a temperature-dependent transition in the microstructural evolution pathway of TiZrNbTaMo, highlighting the strong interplay between chemical partitioning and crystallographic stability in this multi-principal-element alloy.