RAPID CONSOLIDATION PROCESSING OF SILICON-NITRIDE POWDERS

Using a Plasma Assisted Sintering (PAS) process, submicron size, silic on nitride powders were consolidated to >99% of the theoretical densit y (TD) at 1750 degrees C in less than 5 min with retention of the a ph ase and the submicron grain size. The silicon nitride powders were sin tered with 5 wt. % Y2O3 and 5 wt. % Y2O3 + 5 wt. % MgAl2O4 additives. The PAS processing method for the silicon nitride additive mixtures is attractive for retention of fine-grained microstructures favorable fo r superplastic deformation. Post superplastic forming heat treatments to transform the alpha-Si3N4 to lath-like, creep-resistant beta-Si3N4 is another feature of the present processing method.