Influence of WC addition on mechanical properties of (HfNbTaZrTiMo)C‐Co cermet

Abstract

Abstract(HfNbTaZrTiMo)C‐Co high entropy carbide cermet was fabricated by conventional vacuum sintering. The effect of WC addition on the mechanical properties of cermets was also investigated. For cermets without WC addition, with the extension of sintering time, the hardness of cermets first rose and then fell, while the fracture toughness showed a decreasing trend. The increase in sintering temperature led to a decline in hardness and an enhancement of fracture toughness. The (HfNbTaZrTiMo)C‐15 wt. % Co cermet sintered at 1450°C for 2 h had the best comprehensive properties, with the hardness and fracture toughness of 16.36 ± 0.17 GPa and 7.19 MPa·m1/2, respectively. After adding WC, there was a typical black core (undissolved (HfNbTaZrTiMo)C phase)‐gray rim (seven‐component (HfNbTaZrTiMoW)C solid solutions) structure in the cermets. Meanwhile, Mo diffused into WC to form (Mo, W)C solid solutions. The formations of (HfTaZrNbMoTiW)C and (Mo, W)C solid solutions resulted in an improvement in hardness. In addition, since the addition of WC enhanced the wettability between carbides phase and Co phase, the comprehensive properties of cermets were improved. The hardness and fracture toughness of the (HfNbTaZrTiMo)C‐42.5 wt. % WC‐15 wt.% Co cermet sintered at 1450°C for 2 h were 17.42 ± 0.06 GPa and 8.22 MPa·m1/2, respectively.

Effect of WC content on microstructure and mechanical properties of (TiZrHfNbTaMo)C‐15 wt.% Co ceramics

“…The W atoms have not yet diffused into this region due to a low diffusion rate. As also reported in our previous study, 20 a typical black coregray rim structure appeared in HEC 6 -15 wt.% Co ceramics after adding WC. According to the EDS point analysis, the black core and gray rim were undissolved HEC 6 phase and (TiZrHfNbTaMoW)C solid solutions, respectively.…”

“…With the increase of WC content, the average grain size of HEC 6 decreases first and then increases, and the ceramic with addition of 5 wt.% WC has the smallest size of 0.43 ± 0.16 µm. However, compared with the HEC 6 -15 wt.% Co ceramic (0.72 ± 0.18 µm), 20 the grain sizes of all samples after adding WC are reduced. However, relative to the raw HEC 6 powder, there is a slight increase in the average grain size.…”

“…Considering the measurement error, there is no significant difference in the K IC among samples S1, S2, and S4. However, compared with pure HEC 6 -15 wt.% Co ceramic (7.68 ± 0.07 MPa⋅m 1/2 ), 20 the toughness of samples S1-S4 is somewhat improved. Because of the good wettability between WC and Co, the addition of WC improves the wettability between HEC 6 and Co and increases the interface strength.…”

“…The well wettability of Co to WC and a high solubility of WC in Co binder are conducive to the densification of WC-Co hardmetals during the sintering process. 21 According to our previous research, 20 the addition of WC could improve the mechanical properties of (TiZrHfNbTaMo)C-15 wt.% Co ceramics, while the relevant research on the influence of WC content on the microstructure and mechanical properties of (TiZrHfNbTaMo)C-15 wt.% Co ceramics has not been reported. In addition, it is not known whether a small amount of WC can be completely dissolved into the HEC 6 lattice to form (TiZrHfNbTaMoW)C solid solutions.…”

“…Pötschke et al 19 found that among Co, Ni, and FeNi, the HEC ceramics with Co as the binder phase had the best comprehensive properties, which was related to the solubility of carbides in the metal phase, as well as the wettability between metal phase and ceramic phase. In our previous work, 20 the influences of sintering temperature on the properties and microstructure of (HfNbTaZrTiMo)C-15 wt.% Co and (HfNbTaZrTiMo)C-WC-15 wt.% Co ceramics were explored. The increase of sintering temperature led to a decline in hardness and an improvement of toughness.…”