NUCLEATION AND GROWTH OF THE ELONGATED ALPHA'-SIALON

Nucleation and growth behavior of the elongated alpha'-SiAlON grains h ave been studied in alpha'-SiAlON ceramic with an overall composition Y0.48Si10.00Al2.30O1.17N15.29 prepared by hot-pressing at 1825 degrees C. Transmission electron microscopy (TEM) and high resolution electro n microscopy (HREM) have shown that the elongated alpha'-SiAlON grains always contain an alpha-Si3N4 core, implicating heterogeneous nucleat ion operating in the present system. The growth mode is epitaxial. Sel ected area. diffraction (SAD) and HREM analyses reveal that the crysta l structure of the elongated alpha'-SiAlON has dilated and does not st rictly comply with the hexagonal construction, i.e. the c axis tilting by no more than 2 degrees is no longer normal to (001) plane, giving a conclusion that the deformed structure, probably formed by local hig h stress at high temperatures, changes the chemical bonding conditions especially, on (001) plane, leading to faster deposition of atoms on (001) plane than on other planes. Additionally, morphology and growth defects have been studied in this paper. (C) 1997 Elsevier Science Lim ited.