抄録
Si3N4-(5-25) mol%MgO-(2-17) mol%Al2O3 ceramics were sintered in N2 atmosphere of 100kPa at 1973K for 3.6ks. The optical microstructures, mechanical properties, etc., of sintered compacts were investigated as a function of distance from the compact surface and contents of MgO and Al2O3.
It was found that the microstructural heterogeneous layer(HL) was generally formed near the surface of sintered compact. The formation of the HL was attributed to escapes of nitrogen and silicon from the compact surface during sintering. The amount of MgAl2O4 spinel, Si3N4 grain size, etc., in the HL differed in general from those in the inside of compacts. The HL reduced sharply the room-temperature transverserupture strength of the ceramics, owing to facts that the size of defects (pore) which acted as a fracture source was increased and the intrinsic strength was reduced in the HL, compared with those in the inside of compacts.
