Mechanical properties and microstructure of pressureless sintered duophase sialon

Duophase ({alpha}{prime}/{beta}{prime}) sialon is being developed for ceramic engine applications by using the Quickset{trademark} injection molding process, followed by pressureless sintering and a thermal treatment. The sialon had an average four-point flexural strength of 670 MPa at room temperature and 490 MPa at 1370{degree}C. It survived the flexural stress rupture test at 1300{degree}C and 340 MPa for 190 hours. X-ray diffraction (XRD) and transmission electron microscopy (TEM) characterization showed that crystallization of the grain boundary phase improved the high temperature flexural strength of this sialon material. The creep behavior was also found to be affected by the crystallized grain boundary phases. The formation of a yttrium aluminum garnet (YAG) phase and elongated grains yielded better creep resistance. The correlation between mechanical properties and microstructure is discussed. 13 refs., 7 figs