Abstract

An investigation has been made of the use of 2.45 GHz microwave energy to sinter Si 3 N 4 -ZrO 2 (4 mol% Y 2 O 3 stabilized) composites with 5 mass% MgO as a densifying aid at 1600°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 Si 3 N 4 and ZrO 2 to form ZrN. SEM microstructures revealed elongated β-Si 3 N 4 grains with high aspect ratio. Indentation fracture toughness of the composites increased with increasing weight fraction of ZrO 2 . Cracks were propagated intergranularly through Si 3 N4/ZrO 2 interfaces and transgranularly through ZrO 2 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% ZrO 2 and 10 mass% ZrO 2 whereas crack deflection, bridging and microcrack toughening were observed when the amount of ZrO 2 in the composites increased to 25 and 40 mass%.

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