On the extension of the α-SiAlON solid solution range and anisotropic grain growth in Sm-doped α-SiAlON ceramics

Abstract

α-SiAlON samples of the overall composition Sm xSi 12−(m+n)Al m+nO nN 16 − m, with m and n in the ranges 0.6 ≤ m ≤ 1.44 and 1.3 ≤ n ≤ 1.7 ( m = 3 x), were prepared by a hot-pressing technique at 1800 and 1700 °C. Based on X-ray powder diffraction studies and elemental analysis of individual α-SiAlON grains in the obtained ceramic compacts, the extension of the Sm-doped α-SiAlON solid solution range was mapped out. The m-value was found to vary between 0.89 and 1.52 while n was always less than 1.23. Elongated α-SiAlON grains were found preferentially in compacts having overall compositions located slightly outside the oxygen-rich border-line of the homogeneity region of the Sm-doped α-SiAlON phase, i.e. for m ≈ 1.2 and n ≈ 1.3. We also noticed that elongated α-SiAlON grains were formed preferentially perpendicular to the pressure applied in the sintering procedure. All samples exhibited HV10-values in the range 21–22 GPa and K IC -values in the range 4.0–4.7 M Pa m 1 2 .