MICROSTRUCTURAL DEVELOPMENT IN THE INITIAL PERIOD OF SINTERING AND ITS EFFECT ON THE MECHANICAL-PROPERTIES OF SINTER-HIPED SIALONS

Sinter-HIPed or low-pressure sintered sialon ceramics were prepared with different pretreatments in order to study the effect of the initial stage of sintering. The microstructure, flexural strength, hardness and modulus of elasticity were determined after both the initial and the final stages of sintering. Inhomogeneous microstructure with pores of different sizes developed if the sintering schedule was interrupted in a certain temperature range during heating up. Sintering or sinter-HIPing the samples pretreated in this temperature range resulted in dense material with poor flexural strength, while ceramics with high density and considerable strength were obtained if the sintering schedule was conducted without interruption or was interrupted above or under this temperature range. The viscosity change of the liquid phase during the heating period may explain the development of inhomogeneous microstructure.