Si₃N₄-Y₂O₃-ZrO₂-Al₂O₃加圧焼結体の室温強度と組織

抄録

The Si₃N₄-(0-24) mol%Y₂O₃-(0-27) mol%ZrO₂-(4.0-4.6) mol%Al₂O₃ compacts were sintered under 0.5 MPa of nitrogen gas at 2073 K for 7.2 ks. The room temperature mechanical properties such as transverse-rupture strength (σ_m), fracture toughness (K_IC) and hardness (H_V) and the microstructure of the compacts were investigated.
It was found that the compact showed high strength of about 0.7 MPa in the composition range of low Y₂O₃, low-high ZrO₂ or low-medium Y₂O₃+ZrO₂ contents, and it showed low strength of about 0.3-0.5 GPa in the other composition range. The dependences of both K_IC and H_V on the composition were nearly the same as am. The low values of the mechanical properties in the above composition range could mainly be attributed to the appearance of the soft grain boundary phases such as Y₂SiO₅, Y₂₀N₄Si₁₂O₄₈, etc., and also to the largeness of the domain of those grain boundary phases.