Spark Plasma Sintering of Si ₃ N ₄ –BN Ceramic Composites With Improved Properties

ABSTRACT Si 3 N 4 –BN composites were fabricated by spark plasma sintering, and the effects of starting BN particle sizes on microstructure, mechanical properties, and thermal shock resistance of the composites were systematically investigated. The samples with submicron BN effectively refined β ‐Si 3 N 4 grains, resulting in enhanced mechanical properties, including flexural strength and hardness. Among all samples, the 800‐S7B2 sample exhibited the optimal combination of properties, with a flexural strength of 1008 ± 49 MPa, fracture toughness of 6.8 ± 0.1 MPa·m 1/2 , and hardness of 8.1 ± 0.1 GPa. Thermal shock tests indicated that both the samples with submicron BN and the samples with microscale BN retained approximately 90% of their residual flexural strength after thermal shock at 1200°C. Notably, the samples with microscale BN exhibited higher R IV and α cr values due to their greater fracture toughness‐to‐strength ratio, enhancing resistance to crack propagation and resulting in superior thermal shock performance, with residual flexural strength exceeding 90% after thermal shock at 1200°C. These results demonstrate that controlling the BN particle size is an effective strategy to optimize the microstructure, mechanical performance, and thermal shock resistance of Si 3 N 4 –BN composites.