High Strength and High Toughness Anisotropic Silicon Nitrides Fabricated by Forging Technique

Abstract

Grain alignment control to make anisotropic microstructure is one of the most promising techniques to achieve superior mechanical properties in specific directions. Anisotropic silicon nitrides, which were fabricated by a forging technique, can show superior mechanical properties at room temperature as well as at elevated temperatures. A sinter-forged silicon nitride with yttria and alumina additives exhibited very high strength of 2.1GPa at room temperature, meanwhile that with lutetia additive showed high strength of 700MPa at 1500oC. Anisotropic silicon nitrides are also advantageous to achieve higher fracture energy. Such silicon nitrides can show 3~5 times higher fracture energy than isotropic ones. Sinter-forging technique is also applicable to fabricate porous anisotropic silicon nitrides. In this paper, fabrication and mechanical properties of anisotropic silicon nitrides are briefly described.