Phase characterization and properties of AlN-BN composites

High-density AlN-BN particulate composites (5 percent to 30 percent BN) were fabricated by hot pressing using no additive, or 5 percent Y2O3, or 1 percent CaH2 as densification aids. BN remained as a discrete phase and platey particles were oriented perpendicularly to the pressing direction. No significant differences in coefficient of thermal expansion were found for the composites compared with AlN. Flexual strength of AlN-BN composites with no sintering aid and with Y2O3 additive were significantly lower than the corresponding AlN samples at room temperature, but differences were much smaller at 1500 C. Flexural strengths of AlN-BN composites with CaH2 additive were much lower, both at room temperature and at 1500 C. Fracture in all samples was predominantly intergranular. Room temperature Young's modulus determinations revealed decreasing values with increasing amounts of BN. 23 references.