Microstructure evolution of carbon doped Ta-W-Hf alloy by hot forging and annealing

Ta-W-Hf based alloys (T-111 and ASTAR-811C) doped with various carbon contents ((0, 0.01 and 0.025 wt%) were fabricated via high-temperature vacuum sintering and electron beam melting, followed by thermal forging and annealing. Effects of carbon content on the microstructural evolution and carbide distributions in Ta-W-Hf based alloys was investigated in this study. Microstructural analysis revealed that carbon doping effectively refined the grain sizes of the as-forged TaWHf-0.025C alloy owing to the precipitation of carbides along grain boundaries. In contrast, the formation of carbides in the as-forged TaWHf-0.01C alloy was not pronounced. It was found that fine Ta₂C particles formed and uniformly distributed in the grains of the TaWHf-0.01C alloy after annealing, whereas the carbides in the TaWHf-0.025C alloy remained predominantly located at grain boundaries. Furthermore, the interface between the Ta matrix and Ta₂C with crystallographic relationships of [001]_matrix∥[11¯01]_Ta₂C and (200)_matrix∥(1¯011)Ta₂C was identified， These findings highlight the role of carbon content in tailoring carbide distributions and interfacial coherence, which critically influence the mechanical properties and thermal stability of Ta-W-Hf based alloys.