Molecular‐level composition design for efficient synthesis of SiAlON ceramics

Abstract

AbstractSiAlONs are a class of liquid‐phase sintered ceramics with excellent room‐temperature strength and toughness, but whose residual grain boundary glass softens at high temperatures, limiting use in extreme environments. For this reason, efforts are made to minimize the volume of the grain boundary glass while still facilitating full densification. This work describes a potential route for the densification of SiAlONs with very low concentrations of liquid‐phase sintering additive (e.g., rare‐earth oxides such as yttria) by using an organometallic precursor. Solid solution of Al and O in the Si3N4 lattice was accomplished through the incorporation of solute atoms via liquid organic precursor aluminum sec‐butoxide (ASB). Al2O3 powder is conventionally used for this purpose, and the subsequent lattice softening associated with the solid solution helps to facilitate densification. However, a liquid‐phase additive is still essential for the full densification of SiAlONs. Higher densities were obtained from SiAlON powder blends utilizing organometallic ASB than those utilizing alumina powder, allowing for greater densification at very low Y2O3 concentrations. The thermal decomposition of the organic precursor was investigated by high‐temperature scanning electron microscopy, thermogravimetric analysis, and various X‐ray diffraction experiments. Immersion density measurements and lattice parameter refinements were performed for samples sintered with varying Y2O3 concentrations and/or dwell times. Results indicate that ASB‐containing powder blends favor SiAlON formation more strongly than Al2O3‐containing powder blends and favor densification at very low Y2O3 concentration.