Abstract

Different SiAlON composites based on alpha'-SiAlON are investigated, with respect to the phase relationships, densification behavior, and mechanical properties, The compositions are located on a phase-diagram line parallel to the Si3N4-Y2O3 . 9AlN compound in the Si3N4-SiO2-AlN-Al2O3-Y2O3-YN system, Analysis of the reaction sequences shows that the formation of the composites is associated with the transient appearance of Y4Al2O9 (YAM), yttrium-aluminum-garnet (YAG), melilite, and a nitrogen-rich liquid phase, The small shift of compositions on the Si3N4-Y2O3 . 9AlN compound phase-diagram line toward the Al2O3-rich side offers the advantage of a higher sinterability and the removal of the melilite phase from a wide range of compositions containing alpha'-SiAlON and polytypes, The alpha'/beta'-SiAlON composites show better mechanical properties in comparison to pure alpha'-SiAlON and composites of alpha'-SiAlON and polytypes, A post-heat-treatment causes the crystallization of YAG as a grain-boundary phase and leads to excellent strength retention up to temperatures of 1350 degrees C.