Densification of α- and β-Si 3N 4 under pressure

Abstract

Effect of phase transformation on densification, microstructural changes and bonding beetween grains of Si 3N 4, without additives was studied by high pressure hot-pressing using α- and β-Si 3N 4 as starting materials. Densification of Si 3N 4 did not depend on the difference of the phase in starting materials. During the hot pressing of α-Si 3N 4, a drastic change in grain morphology took place with the progress of phase transformation, and the final microstructure showed the existence of self bonding and the development of polyhedral grains. In the hot-pressing of β-Si 3N 4, no appreciable change in grain morphology was observed and densification was proceeded only due to a plastic deformation mechanism. Phase transformation seems to play a significant role in the bonding between grains.