2.45 GHz microwave sintered Si3N4-ZrO2 composites

An investigation has been made of the use of 2.45 GHz microwave energy to sinter SbN4-ZrO2 (4 mol% Y2O3 stabilized) composites with 5 mass% MgO as a densifying aid at 1600 degrees C to avoid the formation of ZrN. XRD phase analysis showed the presence of ZrN in all the sintered samples. Higher temperature developed within the specimen favored the reaction between Si3N4 and ZrO2 to form ZrN. SEM microstructures revealed elongated beta-Si3N4 grains with high aspect ratio. Indentation fracture toughness of the composites increased with increasing weight fraction of ZrO2. Cracks were propagated intergranularly through Si3N4/ZrO2 interfaces and transgranularly through ZrO2 grains with many microcracks in the process zone of the main crack. The results indicated that the dominant toughening mechanisms operating were crack deflection and bridging in the case of 0 mass% ZrO2 and 10 mass% ZrO2 whereas crack deflection, bridging and microcrack toughening were observed when the amount of ZrO2 in the composites increased to 25 and 40 mass%. (c) 2008 The Ceramic Society of Japan. All rights reserved.