Microstructure of hot-pressed h-BN/Si3N4 ceramic composites with Y2O3–Al2O3 sintering additive

The microstructure of hot-pressed h-BN/Si3N4 ceramic composites with Y2O3–Al2O3 sintering additive was characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). SEM examination shows the diameter and aspect ratio of elongated β-Si3N4 grains in the composites to decrease with increasing h-BN content. TEM shows some β-Si3N4 grains in the composites to be unable to develop sufficiently and integrally since h-BN flake limits the growth space for β-Si3N4 grain and reduces the diffusion rate of Si and N in the liquid glass phase. XRD and TEM reveal that the hot-pressed composites are composed of β-Si3N4, h-BN, Y2Si3O3N4 and a glassy phase mainly containing Y and Si. The phase composition of the Si3N4 ceramic matrix is unaffected by h-BN addition.