Mechanical Properties of Silicon Nitride Ceramics Containing Yb₂O₃ Sintering Additives

We have studied the effect of Yb₂O₃ additions on the phase composition and mechanical properties of Si₃N₄ ceramics and shown that, in all of the samples studied, the Yb₄Si₂O₇N₂ compound was a major component of the grain boundary phase, with ytterbium silicates as minor phases, whose content has been found to increase with increasing Yb₂O₃ concentration in the starting powder mixture. The bending strength of the ceramics has a tendency to decrease with increasing sintering additive content at both room temperature and 1600°C. The load–displacement curves obtained at 1600°C point to plastic deformation and creep of the material, the latter increasing with increasing Yb₂O₃ content, which is due to incomplete crystallization of the grain boundary phase.