Patent ID: 7223709

Claim:
A method of making a SiAlON ceramic body that comprises a two phase composite comprising an alpha prime SiAlON phase and a beta prime SiAlON phase, the method comprising the steps of: providing a starting powder mixture that comprises at least about 70 weight percent silicon nitride powder and one or more other powders that provide aluminum, oxygen, nitrogen, and at least two selected rare earth elements to the SiAlON ceramic body wherein the rare earth elements are selected from at least two groups of the following three groups of rare earth elements wherein Group I comprises La, Ce, Pr, Nd, Pm, Sm and Eu, and Group II comprises Gd, Tb, Dy and Ho, and Group III comprises Er, Tm, Yb and Lu, wherein the silicon nitride powder in the starting powder mixture contains essentially zero weight percent beta silicon nitride; and consolidating the starting powder mixture to form a ceramic body comprising a two phase composite comprising an alpha prime SiAlON phase and a beta prime SiAlON phase, and the alpha prime SiAlON phase containing one or more of the selected rare earth elements excluding La and Ce, and the ceramic body having a composition falling within the area bounded by the trapezoid defined by points A, B, C and D in FIG. 7 .