Microstructure and mechanical properties of (Ti, W, Mo, Nb, Ta) (C0.78, N0.22) high entropy cermets with 5–25 wt% Co–Ni binders

In this study, high entropy (Ti0.6,W0.1,Mo0.1,Nb0.1,Ta0.1)(C0.78,N0.22) ceramics (HECN) powders were synthesized by carbothermal reduction nitridation. (100-x) HECN-(x/2) Co-(x/2) Ni (x = 5–25 wt%) cermet was prepared by vacuum sintering. The relationship between microstructure and mechanical properties of HECN-based cermet sintered at 1450 °C and 1500 °C was studied. The results show that the second phase (W,Mo,Ti)3+x(Co, Ni)3−xC appears at both sintering temperatures, and its content decreases with the increase of binder Co, Ni content and sintering temperature; At the same time, the grain size of the hard phase of the cermet grows with the increase of Co and Ni content. In terms of mechanical properties, at both sintering temperatures, the cermet showed a decrease in hardness and an increase in fracture toughness with the increase of Co and Ni content, while the bending strength increased and then decreased. Among them, when the content of Co and Ni is 20 wt%, the bending strength of HECN-based cermet sintered at 1450 °C is the best, and the bending strength reaches 1640 MPa. This is attributed to the combined influence of many elements in high entropy cermet, which on the one hand leads to serious lattice distortion; On the other hand, improving the wettability and density of the cermet has a strengthening effect on the cermet. In addition, with the increase in Co and Ni content, the plastic deformation of the bond phase will inhibit crack propagation. The main paths are crack deflection and crack bridging, which increase the energy required for crack propagation and lead to a gradual increase in fracture toughness.