Abstract
The mechanical properties of ceramics have been tremendously improved through well-organized control of the microstructure elements during the past few decades. This paper intends to describe how mechanical properties change via such microstructural controls, taking several examples of such research efforts in silicon nitride, one of the most important engineering ceramics. These include (1) super strong silicon nitride with > 2 GPa strength via refinement and alignment of fibrous grains, (2) super heat resistant silicon nitride with strength retention up to 1500 ˚C and toughness of ～800 J/m2 (double that of cast iron) via alignment of fibrous grains and adjustment of grain boundary phases, (3) porous silicon nitride via control of grain morphologies, and (4) porous silicon nitride with high strength (> 1 GPa), and high toughness (300 − 500 J/m2; far higher than that of the dense) via alignment of fibrous grains and pores.
