Ff. Xu et al., Influences of intergranular precipitates on the structure and chemistry ofinterface in silicon nitride materials, SURF INT AN, 31(2), 2001, pp. 59-67
Pure beta -Si3N4 is used in the present work as the starting powder to synt
hesize alpha -sialon (alpha') ceramics; 5 wt.% alpha'-seeds are added to pr
omote nucleation of cu-sialon. Transmission electron microscopy (TEM) obser
vations reveal an inhomogeneous microstructure in which intergranular preci
pitates are produced in some regions where the structure and the chemistry
of the interfaces vary significantly. The surfaces of the sialon grains adj
acent to the precipitates are always rounded and corrugated, and the interf
acial thickness increases. An internal band structure is usually discovered
in these grains. Chemical analyses find that a small number of Y ions have
been incorporated into the surface lattice. A possible formation mechanism
of the corrugated surface is proposed and suggests a redissolution process
of sialon grains during the crystallization of intergranular precipitates
and an enhanced growth during cooling that is governed by interface-control
led kinetics. The increased number of growth sites eventually gives rise to
a corrugated surface. Copyright (C) 2001 John Wiley & Sons, Ltd.