PHASE-SEPARATION AND TOUGHENING OF SIC AIN SOLID-SOLUTION CERAMICS

SiC-AIN solid-solution ceramics were prepared by pressureless sintering using Al2O3 and Y2O3 as the sintering additives. The resulting ceramics were subjected to annealing treatments over a range of temperatures from 1400-degrees-C to 1800-degrees-C in the spinodal region. The fracture toughness of the annealed ceramics was examined, by the indentation method, in relation to the annealing temperature and annealing time. X-ray diffraction profiles revealed that phase separation occurred during annealing. In ceramics containing 50 mol % SiC annealed at 1800-degrees-C, the morphology of the phase separation is the characteristic modulated stratiform structure. Energy-dispersive X-ray spectroscopy (EDS) showed that the structure consisted of alternations of silicon-rich and aluminium-rich composition. The fracture toughness of the annealed ceramics increased compared to the as-sintered solid-solution ceramics. The phase separation is expected to contribute to the toughening of ceramics with nanometre-scale texture.