Abstract
The solidification structures of the liquid phase formed during sintering, such as domain structures (crystal grain) of Mg2SiO4 and MgAl2O4 phases, and the room temperature mechanical properties of Si3N4-(10-20)mo1%MgO-5.5 mo1% Al2O3 ceramics were investigated as a function of cooling rate (0.017-1Ks-1) after sintering. The sintering temperature, time and atmosphere were 1973 K, 3.6 ks and nitrogen of 0.1 MPa, respectively.
When the cooling rate became larger, the domain structures of the Mg2SiO4 and MgAl2O4 phases became finer and at the same time the amount of both phases decreased (the amount of glassy phase probably increased). The transverse-rupture strength of the ceramics increased with increasing cooling rate. This result would be attributed to both the improved toughness of ceramics caused by the refinement of microstructure and the decreased size of defect (pore) acting as a fracture source. The microstructural heterogeneous surface layer of sintered compact and the hardness were also varied by the cooling rate.
