PROCESSING AND MECHANICAL-PROPERTIES OF SI3N4 WITH LOW CONTENT OF ADDITIVES

In this work Si3N4 materials with low additive content have been produced and characterized. In doing so the handling properties could be found out and the processing technology was optimized for this kind of materials. The applied Si3N4 powder showed an extremely low oxygen content and Al2O3 and Y2O3 have been used as sinter additives. The material was processed in a conventional mixing milling procedure with a subsequent gas pressure sintering process. The samples reached four point bending strengths up to 980 MPa at room temperature and up to 500MPa at 1200 degrees C. hence, the K-IC-values were in the order of 6.5MPam(1/2). Oxidation tests were carried out at 1400 degrees C in flowing oxygen and revealed an extremely good oxidation resistance compared to standard compositions. The mechanical properties with regard to the variations of the process will be discussed.