In this paper, a high-entropy composite bulk ceramic of (Hf_0.2Zr_0.2Ti_0.2Nb_0.2Ta_0.2)N/silicon carbide (i.e., HEN-SiC) was fabricated via spark plasma sintering (SPS) at 2100°C with submicron-sized single-phase (Hf_0.2Zr_0.2Ti_0.2Nb_0.2Ta_0.2)N (HEN) powder as a raw material and SiC particles as a sintering aid. The crystal structure, phase composition, and grain size/morphology of the composite were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and energy dispersive spectroscopy. The relative density and the mechanical property (i.e., bending strength, Vickers’ hardness and fracture toughness) of the composite bulk ceramic were analyzed. The results show that the relative density of the composite bulk ceramics incorporated with SiC particles content increasing from 0 to 10.0 wt.% increases from 93.08±0.13% to 99.12±0.12%. The high-entropy composite bulk ceramic with SiC particles content of 10.0 wt.% exhibits the optimum mechanical property (i.e., Vickers’ hardness of 23.34±0.67 GPa, fracture toughness of 4.35±0.13 MPa·m^1/2, and bending strength of 409±11 MPa), compared to the ceramic without SiC particles (i.e., Vickers’ hardness of 19.16±0.56 GPa, fracture toughness of 3.78±0.09 MPa·m^1/2, and bending strength of 335±11 MPa). It is indicated that SiC particles can be distributed and filled at the HEN grain boundaries in the ceramic matrix, promoting the composite densification via pinning grain boundaries and inhibiting the grain growth. The enhanced fracture toughness can be mainly due to fine-grain toughening besides lamellar/chain structures toughening. The use of SiC as a sintering aid can promote the densification and fracture toughness of high-entropy nitride bulk ceramics, providing a promising approach for the preparation of high-density, high-performance high-entropy nitride bulk ceramics.

Based on the promotion and application of green and low-carbon technology, this study aims to develop a high-safety performance cement concrete incorporating a large dosage of fly ash (FA). The safety and effect of FA content on the mechanical properties of FA composited cement were studied through compressive strength, flexural strength, and microscopic tests. The results show that when the FA replaced 20% cement, the properties of concrete were the best in this study. The flexural strengths and compressive strengths of the standard cured concrete for 28 days with 20% FA content are 0.82 MPa and 4.32 MPa larger than that of the pure cement concrete. The XRD and SEM analysis suggested that the mechanical properties of the composite cement FA system are improved significantly since the replacement of cement by FA promotes secondary hydration of calcium hydroxide in the concrete, leading to a more compact and safe interface between cement and FA.