Method of making a SiAION ceramic

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 tat 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;
• and wherein the beta-silicon nitride content of the silicon nitride powder has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent of the silicon nitride powder;
• 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.

A method for 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 includes silicon nitride powder and one or more powders that provide aluminum, oxygen, nitrogen, a liquid phase-forming element, and at least one selected rare earth element to the SiAlON ceramic body wherein:
• in the case of a single of the selected rare earth element, the selected rare earth element is selected from any of the following groups wherein Group I comprises Pr, Nd, Pm, Sm and Eu, and Group II comprises Gd, Tb, Dy and Ho, and Group III comprises Er, Tm, Yb and Lu;
• and in the case of a plurality of the selected rare earth elements, the rare earth elements are selected from at least two groups of the following three groups of rare earth elements wherein Group IA comprises La, Ce, Pr, Nd, Pm, Sm and Eu, and Group II comprises Gd, Tb, Dy and No, and Group III comprises Er, Tm, Yb and Lu;
• 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 silicon nitride powder comprises at least about 70 weight percent of the starting powder mixture, the silicon nitride powder has a beta-silicon nitride content that has a lower limit equal to zero weight percent and an upper limit equal to about 1.6 weight percent of the silicon nitride powder.