Fracture behavior and toughness of h-BN/Si₃N₄ ceramic composites

h-BN/Si₃N₄ composites were fabricated by hot-pressing using sub-micrometer sized α-Si₃N₄, h-BN powders and Y₂O₃-Al₂O₃ sintering additives. The effects of h-BN content on the fracture behavior and toughness of the h-BN/Si₃N₄ ceramic composites were investigated. The results reveal that the diameter and aspect ratio of elongated β-Si₃ N₄ grains in the composites decrease with increasing h-BN content. The dominant fracture behavior of the monolithic Si₃N₄ is intergranular fracture. After adding h-BN into Si₃N₄ ceramic, the intergranular and transgranular fracture are both significant in the composites containing 6% and 8% h-BN (volume fraction). However, the dominant fracture behavior of the composites containing 6% h-BN is intergranular. The fracture toughness of the h-BN/Si₃N₄ ceramic composite decreases with increasing h-BN content; however, the reduction extent is not pronounced due to the effect of the h-BN particles on the cracks propagation.