HOT ISOSTATIC PRESSING OF SIC/SI3N4 COMPOSITE WITH RARE-EARTH-OXIDE ADDITIONS

SiC/Si3N4 composites with rare earth oxide additions have been prepared by glass encapsulated hot isostatic pressing at 1850 degrees C and 200 MPa pressure. Mechanical properties and microstructures of the sintered samples have been studied. It is shown that different molar ratios of La2O3 to Y2O3 and the total amount of La2O3 and Y2O3 additions can affect the mechanical properties significantly. With 3 wt% La2O3 + Y2O3 additions, lower La2O3/Y2O3 molar ratio exhibits higher bending strength and median fracture toughness, but relatively lower Vickers hardness. For addition of 6 wt% La2O3 + Y2O3, the higher bending strength, Vickers hardness and fracture toughness correspond to a certain La2O3/Y2O3 molar ratio of 1.5, 1.0 and 0.5, respectively. SEM observation shows that the SiC matrix composite with fine grain size and homogeneous microstructure can be obtained.