A series of dual-phase high-entropy ultrahigh temperature ceramics (DPHE-UHTCs) are fabricated starting from N binary borides and (5-N) binary carbides powders. >~99% relative densities have been achieved with virtually no native oxides. These DPHE-UHTCs consist of a hexagonal high-entropy boride (HEB) phase and a cubic high-entropy carbide (HEC) phase. A thermodynamic relation that governs the compositions of the HEB and HEC phases in equilibrium is discovered and a thermodynamic model is proposed. These DPHE-UHTCs exhibit tunable grain size, Vickers microhardness, Young' and shear moduli, and thermal conductivity. The DPHE-UHTCs have higher hardness than the weighted linear average of the two single-phase HEB and HEC, which are already harder than the rule-of-mixture averages of individual binary borides and carbides. This study extends the state of the art by introducing dual-phase high-entropy ceramics (DPHECs), which provide a new platform to tailor various properties via changing the phase fraction and microstructure.
@article{arxiv.2002.09756,
title = {Dual-Phase High-Entropy Ultra-High Temperature Ceramics},
author = {Mingde Qin and Joshua Gild and Chongze Hu and Haoren Wang and Md Shafkat Bin Hoque and Jeffrey L. Braun and Tyler J. Harrington and Patrick E. Hopkins and Kenneth S. Vecchio and Jian Luo},
journal= {arXiv preprint arXiv:2002.09756},
year = {2020}
}