ON THE EXTENSION OF THE ALPHA-SIALON SOLID-SOLUTION RANGE AND ANISOTROPIC GRAIN-GROWTH IN SM-DOPED ALPHA-SIALON CERAMICS

alpha-SiAlON samples of the overall composition SmxSi12-(m+n)Alm+nOnN1 6-m with m and n in the ranges 0.6 less than or equal to m less than o r equal to 1.44 and 1.3 less than or equal to n less than or equal to 1.7 (m = 3x), were prepared by a hot-pressing technique at 1800 and 17 00 degrees C. Based on X-ray powder diffraction studies and elemental analysis of individual alpha-SiAlON grains in the obtained ceramic com pacts, the extension of the Sm-doped alpha-SiAlON solid solution range was mapped out. The m-value was found to vary between 0.89 and 1.52 w hile n was always less than 1.23. Elongated alpha-SiAlON grains were f ound preferentially in compacts having overall compositions located sl ightly outside the oxygen-rich border-line of the homogeneity region o f the Sm-doped alpha-SiAlON phase, ie. for m approximate to 1.2 and n approximate to 1.3. We also noticed that elongated alpha-SiAlON grains were formed prefererentially perpendicular to the pressure applied in the sintering procedure. All samples exhibited HV10-values in the ran ge 21-22 GPa and K-1c-values in the range 4.0-4.7 MPa m(1/2). (C) 1997 . Published by Elsevier Science Limited. All rights reserved.