Fracture toughness of Si3N4 ceramic composites: Effect of texture

Silicon nitride (Si3N4) ceramics with Al2O3, MgO and Y2O3 as sintering additives were fabricated via hot-pressing sintering and gas pressure sintering, respectively, focusing on the texture and fracture toughness. The hardness and fracture toughness on the plane perpendicular and parallel to the hot-pressing direction were different in the hot-pressing sintered samples, and similar values were obtained in the gas pressure sintering. The orientation distribution function (ODF) analyses via X-ray diffraction measurements revealed the presence of {11 (2) over bar0} < 0001 > type texture in the hot-pressing sintered samples. This suggested that the {0001} planes of most rod-shaped beta-Si3N4 grains were oriented in the hot-pressing direction or their c-axes were oriented towards the radial directions of the sintered cylinder-shaped samples. The presence of such a beta-Si3N4 grain texture led to the anisotropy in fracture toughness, with its values changing from 9.3-11.3 MPa m(1/2) with increasing indentation angles on the plane parallel to the hot-pressing direction.