The effect of particle size gradation on the microstructure, mechanical and thermal physical properties of BN-ZrO2-SiC composites

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By regulating the proportion of large and small boron nitride particles, BN-ZrO2-SiC composites with particle gradation are designed. Through the strategy of particle grading, small particles could be filled into the “card-house structure” formed by h-BN with large particle size, promoting the densification process. At the same time, this also shortens the mass transfer distance between particles, which is conducive to the mass transfer during the hot-pressing sintering. On the basis of achieving the second phase strengthening effect, the performance of hexagonal boron nitride composite has been further improved. The results demonstrate that by a volumetric proportionality of 6:4 between the constituent large particle (7 μm) and small (1 μm) particle. Thus, the BN-ZrO2-SiC composite with high density has been successfully fabricated at a sintering temperature of 1700 °C under 25 MPa. The optimization mechanical properties of BN-ZrO2-SiC composites are achieved when the volumetric ratio of large particle (7 μm) to small (1 μm) particle is 6:4. The optimal flexural strength, fracture toughness, Vickers’ hardness and elastic modulus is 187 ± 4 MPa, 2.2 ± 0.3 MPa m1/2, 0.74 ± 0.06 GPa, and 57 ± 1.1 GPa, respectively. Comparing to the h10 and H10 sample, the thermal conductivity of samples with particle size gradation has been improved, especially the H8h2 and H4h6 samples. The thermal conductivity is significantly enhanced from 14.79 W/(m·K) to 16.83 W/(m·K).