Synthesis, microstructure, and properties of novel series of (Ti, W, Mo, Nb, Ta) (C0.78, N0.22) high entropy ceramic-based cermets

Abstract

Five high-entropy carbonitride ceramic (HECN) powders consisting of pentavalent cations (Ti,W,Mo,Nb,Ta) (C0.78,N0.22) are synthesized by the carbothermal reduction-nitridation (CRN) method. Subsequently, a series of 85HECN-7.5Co-7.5Ni(wt.%) cermet is fabricated employing the powder metallurgy method. The phase constitution, microstructure, and composition distribution of the HECN powders are analyzed. The synthesis temperature of the HECN powders is reduced by 100 °C compared to the non-high-entropy (Ti,Me) (C,N) ceramic powder when ΔSmix >1.5R, which demonstrates that the high entropy effect promotes the synthesis of solid solution powder. A uniform element distribution, 600 nm single-phase (Ti0.6,W0.1,Mo0.1,Nb0.1,Ta0.1) (C0.78,N0.22) high-entropy ceramic solid solution powder, could be synthesized through the CRN at 1400 °C for 2 h under a 2 kPa N2 atmosphere. Subsequently, five types of (Ti,W,Mo,Nb,Ta) (C0.78,N0.22)-Co-Ni high-entropy cermets are prepared via vacuum sintering at 1500 °C for 1 h. Among them, the (Ti0·6W0·1Nb0·1Ta0·1Mo0.1) (C0.78,N0.22)-Co-Ni cermet exhibited the most outstanding performance with a Vickers hardness of 2053.4 HV, fracture toughness of 12.3 MPa m1/2, and TRS of 1220 MPa, which present an increase of 17.0 %, 16.2 %, and 60.0 %, respectively, compared with the non-high-entropy TiCN–Co–Ni cermet. It was attributed to the addition of high-entropy ceramic powders, which resulted in fine grain strengthening, severe lattice distortion, and long crack deflection paths. This study presents a novel approach for the preparation of high-entropy Ti(C,N)-based cermets.