Tailored microstructures of silicon nitride ceramics

The microstructural evolution in Si3N4 ceramics is analysed by studies
of pressureless and gas pressure sintered materials.Parameters
controlling the size and aspect ratio of elongated grains are
discussed, based on the assumption that only pre-existing beta-Si3N4
particles of the starting powder grow.Furthermore, it shown that the
grain morphology is also controlled by the sintering additives due to
their influence on the surface energy of Si3N4 crystals.
Microstructures are also related to strength as well as toughness
measurements at room temperature.It is demonstrated that strength
decreases with increasing grain size, but controlled grain growth could
significantly improve fracture toughness, reliability and thermal
shock-behaviour.