Microstructural development in AlN (YF 3) ceramics

Abstract

Microstructural developments in AlN ceramics with added YF 3 as sintering aid have been studied by sintering at 1880 °C. In particular, the wetting ability of the secondary phase and the grain growth have been systematically studied by varying the sintering time and the type of embedding of the samples during sintering. The wetting ability of the Al-Y-O-containing phase on AlN grains was found to be dependent on the content of oxygen impurities on the AlN grain surface. The composition (Al 5Y 3O 12 = YAG, AlYO 3 = YAP or Al 2Y 4O 9 = YAM) of the secondary phase and the nitrogen solubility in the Al-Y-O phase seem to have only minor importance for the wetting conditions. The observed grain growth is influenced by the wetting ability of the secondary phase which is determining the contiguity of the samples. From samples showing good wetting, the grain growth mechanism in AlN is determined to be diffusion controlled. In the non-wetting samples, the rate of grain growth is nearly independent of the amount of secondary phase present in the microstructure because the solid-liquid contact area is small.