Mechanical Property and Oxidation Behavior of Self-Reinforced Si3N4 Doped with Re2O3 (Re=Yb, Lu)

In this work, self-reinforced silicon nitrides with β-Si₃N₄ seeds doped with Re₂O₃ (Re=Yb, Lu) were investigated. Firstly, the two kinds of seeds were obtained by heating α-Si₃N₄ powder with Yb₂O₃ or Lu₂O₃, respectively. Then the self-reinforced silicon nitride ceramics were prepared by HP-sintering of α-Si₃N₄ powder, Re₂O₃ as additive, and the as-prepared seeds. Oxidation test was carried out at 1400°C in air for 100 h with thermogravimetry analysis (TGA) measurement. Mechanical properties, scanning electronic microscopy microstructures, and X-ray diffraction patterns were measured before and after oxidation. The results indicated that the introduction of the seeds doped with Re₂O₃ (Re=Yb, Lu) could obviously increase the toughness and keep the room temperature and high-temperature strength of the ceramics at high values. After oxidation, the crystalline phase in grain boundary changed and the mechanical properties decreased. TGA showed a parabolic weight gain and the oxidation mechanism was discussed.