Solidification microstructures of multielement carbides in the high entropy Zr-Nb-Hf-Ta-Cx system produced by arc melting

Abstract

Multielement, high entropy carbides are a new class of refractory materials typically manufactured by solid-state synthesis. Although high entropy alloys are usually produced by solidification of a melt, the solidification of high entropy carbides has not been investigated to date. Herein, we report the first arc melting study of the solidification microstructures of the Zr-Nb-Hf-Ta-Cx system. The results highlight the presence of elemental segregation in interdendritic regions whose composition depends on the carbon load (i.e., the composition of the primary solidification phase changes with the amount of carbon in the melt). Duplex microstructures containing two distinct multielement carbides, possessing hardness as high as 30 GPa, are obtained. Interestingly, under certain conditions, there is a perfect “crystallographic continuity” (no grain boundaries and cell parameter variations) between the two phases, though their composition differs. Arc melting produces new and exotic microstructures not observed in materials processed in the solid state.