B4C‒15 vol% TiB2 composites were fabricated by in situ reactive spark plasma sintering with B4C, TiC, and amorphous B powders as the raw materials. The size coupling of initial B4C and TiC particles was optimized based on the reaction mechanism to derive B4C‒TiB2 composites with enhanced microstructure and properties. During the reactive sintering, fine B4C–TiB2 particles were firstly formed by an in situ reaction between TiC and B. Then, large B4C particles tended to grow at the cost of small B4C particles. The in situ TiB2 grains gradually grew up and interconnect, distributing around the large B4C grains to form an intergranular TiB2 network. The results showed that the B4C‒15 vol% TiB2 composite prepared from 3.12 μm B4C powder and 0.80 μm TiC powder had the optimal comprehensive properties, with a relative density of 99.50%, a Vickers hardness of 31.84 GPa, a flexural strength of 780 MPa, a fracture toughness of 5.77 MPa·m1/2, as well as an electrical resistivity of 3.01 × 10−2 Ω·cm.
In this study, Si3N4−Si2N2O composite ceramics were prepared through a two‐step combination of the direct nitriding method and spark plasma sintering method with diamond‐wire saw silicon waste in the photovoltaic industry as raw material. The whole holding time at the constant temperature of the preparing process only lasts 35 min, in which the nitriding time only takes 30 min and the sintering time only takes 5 min. The effects of the Fe2O3 additive on the nitriding and sintering process were investigated in detail. The results show that the Fe2O3 additive accelerates the nitriding process by promoting the formation and diffusion of the gas phase and reducing the apparent activation energy of the reaction between the gas phase containing silicon and N2. Meanwhile, the Fe2O3 additive also promotes the sintering process by lowering the eutectic temperature of the SiO2−Al2O3 and the SiO2−Y2O3 binary system. The optimal technical parameters follow the nitriding temperature of 1400°C, the nitriding time of 30 min, the sintering temperature of 1800°C, and the sintering time of 5 min. The Si3N4−Si2N2O composite ceramic prepared under the above conditions exhibits good performance with an apparent porosity of 2.7%, Vickers hardness of 16.54 GPa, and fracture toughness of 4.1 MPa·m1/2.
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