Patent ID: 7094717

Claim:
A method for making a crystallized ceramic body containing a two phase composite comprising an alpha prime SiAlON phase that contains ytterbium and a beta prime SiAlON phase, the process comprising the steps of: blending together a starting powder mixture that upon densification forms the SiAlON ceramic, the starting powder includes at least about 70 weight percent silicon nitride powder wherein the silicon nitride powder contains beta silicon nitride in an amount less than or equal to about 1.6 weight percent of the silicon nitride powder, and the starting powder further including one or more powders that contribute aluminum, oxygen, and nitrogen to the beta prime SiAlON phase and aluminum, oxygen, nitrogen and ytterbium to the alpha prime SiAlON phase; and densifying the starting powder mixture to form a densified SiAlON ceramic; and heat treating the densified ceramic body so as to form the crystallized ceramic body wherein the alpha prime SiAlON phase comprises at least about 20 weight percent of the two phase composite.