Densification behavior and properties of Y2O3-containing alpha-SiAlON-based composites

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.