Effect of Re2O3–MgO additives on the microstructure evolution and properties of β-Si3N4 ceramics

Abstract β-Si3N4 ceramics were prepared by gas pressure sintering using α-Si3N4 powders, β-Si3N4 whiskers and Re2O3–MgO (Re = Y, La, Gd, Ho, Yb) additives. The phase transformation from α-Si3N4 to β-Si3N4 was completed after sintering. The distribution of oxide particles gets more homogeneous with the increase of the atomic number of the Re element, resulting in an increase of the grain size and the formation of elongated β-Si3N4 grains, which significantly influence the fracture mode and the mechanical properties of β-Si3N4 ceramics. The thermal conductivity of β-Si3N4 ceramics is determined by both the grain size and the distribution homogeneity of oxide particles, thus showing no regular trend between different specimens.