Microstructure, Mechanical and Tribological Properties of High-Entropy Carbide (MoNbTaTiV)C5.

High-entropy carbide (NbTaTiV)C4 (HEC4), (MoNbTaTiV)C5 (HEC5), and (MoNbTaTiV)C5-SiC (HEC5S) multiphase ceramics were prepared by spark plasma sintering (SPS) at 1900 to 2100 °C, using metal carbide and silicon carbide (SiC) as raw materials. Their microstructure, and mechanical and tribological properties were investigated. The results showed that the (MoNbTaTiV)C5 synthesized at 1900-2100 °C had a face-centered cubic structure and density higher than 95.6%. The increase in sintering temperature was conducive to the promotion of densification, growth of grains, and diffusion of metal elements. The introduction of SiC helped to promote densification but weakened the strength of the grain boundaries. The average specific wear rates for HEC4 were within an order of magnitude of 10-5 mm3/N·m, and for HEC5 and HEC5S were within a range of 10-7 to 10-6 mm3/N·m. The wear mechanism of HEC4 was abrasion, while that of HEC5 and HEC5S was mainly oxidation wear.

Microstructure and Properties of Ti(C,N)-Based Cermets with AlxCoCrFeNiTi Binder.

AlxCoCrFeNiTi (x = 0.1, 0.3, 0.6, 1) powders were prepared via mechanical alloying and were used as binders for SPS-produced Ti(C,N)-based cermets. The effects of AlxCoCrFeNiTi binder on phase composition, morphology, room-temperature mechanical properties, and oxidation resistance of cermets were studied. The research showed that cermets with AlxCoCrFeNiTi binders exhibited a more homogeneous core-rim structure than cermets with cobalt binders. The Vickers hardness and fracture toughness of cermets with AlxCoCrFeNiTi binders increased with the aluminum molar ratio due to the grain refinement and solid solution strengthening effect of carbonitrides. After static oxidation at 1000 °C, the mass gain of the cermets with AlxCoCrFeNiTi binders changed according to a quasi-parabolic law, and the lowest mass gain was obtained in the cermet with Al0.6CoCrFeNiTi binder. The oxidation kinetics curve of the benchmark cermet with cobalt followed a linear law. The oxidation product of Ti(C,N)-based cermet with cobalt was rich in TiO2, and the Ti(C,N)-based cermets with AlxCoCrFeNiTi binders were transformed into complex oxides, such as NiMoO4, NiWO4, FeMoO4, Fe3Ti3O9, and Ni3TiO7. The oxide layer on the cermet with Al0.6CoCrFeNiTi appeared to be dense and protective, which inhibited the diffusion of oxygen into the cermet and improved the oxidation resistance of the final product.

CoAl-layered double hydroxide nanosheets as an active matrix to anchor an amorphous MoSx catalyst for efficient visible light hydrogen evolution.

CoAl-layered double hydroxide nanosheets (CoAl-NSs) could serve as an active matrix to effectively anchor amorphous MoSx nanoparticles with high dispersion and the formation of an additional active "CoMoS" phase. The resulting CoAl-NSs/MoSx catalyst showed 13 times higher H2 evolution activity than free MoSx nanoparticles from an erythrosin B-triethanolamine (ErB-TEOA) system under visible light.