PREPARATION AND PROPERTIES OF X-SIALON

X-sialon has been produced by hot pressing Si3N4-Al2O3-SiO2 powder mix tures and Si3N4 powder-mullite gel mixtures at 1650 degrees C. The for mation mechanism of X-sialon has been studied and is correlated with t he processing technique for the two preparation routes. Microprobe ana lysis of the obtained X-sialon phase, combined with previous observed compositions and literature formulae suggests that, at 1650 degrees C, X-sialon exists as a narrow solid solubility region on the Si3N4-mull ite line in the Si3N4-SiO2-Al2O3-AlN phase diagram. The physical, mech anical and chemical properties of X-sialon have been evaluated. X-sial on has a modest hardness of 1280 kg mm(-2), a fracture toughness of 1. 7 MPa m(1/2), and an elastic modulus of 213 GPa. X-sialon exhibits exc el lent chemical stability in contact with iron-based alloys at 1200 d egrees C.