Processing, characterization and mechanical properties of SiAlONs produced from low cost beta-Si3N4 powder

SiAlON ceramics have been known for many years as prime candidate materials in structural applications at ambient and high temperatures involving superior mechanical and/or chemical processes. In spite of their excellent properties, the utilization of SiAlONs has remained limited till today due to the high cost of raw materials and processing. In order to circumvent this problem, low cost refractory grade, coarse, impure, less sinter active beta-Si3N4 powder was used to produce SiAlON ceramics with satisfactory mechanical properties. In this article, the processing challenges in the production of SiAlON ceramics with beta-Si3N4 powder were discussed. The process parameters obviously affect the phase assemblage, densification, microstructural and mechanical properties of final SiAlON ceramics. Processed beta-Si3N4 powder characteristics are majorly investigated by SEM-EDX, XRD, XRF, laser particle sizer and elemental analyser. The existence of undesirable impurities in the beta-SiAlON crystal structure because of the use of impure Si3N4 powders has been shown to be tolerable by TEM microstructural analysis. Mechanical properties are in general evaluated by Vickers indentation method. Wear behaviour of the cost effective SiAlONs were compared with commercially available ceramic materials which are commonly being used in wear applications. Initially the use of such powders to produce materials for engineering applications proved challenging, however, satisfactory results have been obtained by the optimization of the initial chemical composition and process parameters.