Outstanding specific yield strength of a refractory high-entropy composite at an ultrahigh temperature of 2273 K

We reported on the mechanical properties and microstructural evolution of a W 20 Ta 30 Mo 20 C 30 (at.%) refractory high-entropy composite (RHEC). The RHEC exhibited outstanding yield strength at both 2273 and 1873 K. Microstructural investigations revealed that the as-cast RHEC had a triple-phase structure consisting of FCC dendrites, HCP matrix, HCP-BCC eutectic structure, and FCC-BCC eutectoid structure, and exhibited high-density defects owing to the complex phase transformations during solidification. After annealing at 2273 K, the precipitation of the BCC phase from the FCC dendrites and the decomposition of the HCP phase into the FCC-BCC eutectoid structure was observed to significantly refine the grain sizes of all triple phases. After compression at 2273 K, the ceramic phases and solid solution precipitated out from each other, which helps to avoid persistent softening after the yielding of RHEC. Further analyses suggested that the dominant deformation mechanisms of the BCC phase and HCP phase are dislocation glide and transformation-induced plasticity; whereas those of the FCC phase are twinning- and transformationinduced plasticity. The outstanding yield strength of this RHEC at ultrahigh temperatures may originate from the high-content ceramic phases and the structural metastability of the multi-principal composition. These findings provide a novel strategy to design RHECs by alloying high-content nonmetallic elements, which contributes to further breaking through their performance limits at ultrahigh temperatures. & COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Automated summary

This study investigated the mechanical properties and microstructural evolution of a W 20 Ta 30 Mo 20 C 30 (at.%) refractory high-entropy composite (RHEC). The RHEC exhibited outstanding yield strength at high temperatures and had a complex triple-phase structure. Microstructural investigations showed significant grain refinement after annealing and compression, with different deformation mechanisms identified for each phase. The high-content ceramic phases and structural metastability were found to contribute to the outstanding yield strength at ultrahigh temperatures.