Microstructural design and mechanical properties of porous silicon nitride ceramics

In structural materials, pores are generally believed to deteriorate the mechanical reliability. This paper, however, shows that pores can cause improved or unique performance when the sizes, shapes, and orientation of pores as well as grains are controlled in porous silicon nitrides. Two types of porous materials are dealt with; one is isotropic porous silicon nitrides, where fibrous grains are randomly oriented, and the other is for anisotropic porous silicon nitrides, where fibrous grains are substantially aligned in one direction. Particular emphasis is placed in substantially improved properties including fracture energy, fracture toughness, strain tolerance, and thermal shock resistance of the porous materials, even compared with those of the dense materials.