Self Reinforced Behavior of Silicon Nitride Ceramics by Reaction Bonding Method

Abstract

Microstructure control of Si3N4 ceramics using reaction bondiing method with mixtures of the two types of Si powder is discussed. Specifically, the effect of the Si powder size on mechanical properties of reaction bonded Si3N4 ceramics is investigated. In order to increase the fracture toughness without decreasing the bending strength of the ceramics, it is effective to mix fine and coarse Si powders. The fracture toughness of nitrided bodies using mixtures of 0.4μm Si powder and 3μm or 11μm Si powder was 3.7MPa. m1/2, which is 1.5 times higher than that of using fine Si powder alone. The bending strength (300MPa) was the same as the nitrided body using fine Si powder alone. The fracture toughness was improved by the dispersing coarse Si3N4 grains in fine grained Si3N4 matrix.