Abstract
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 β-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 β-Si3N4 powder were discussed. The process parameters obviously affect the phase assemblage, densification, microstructural and mechanical properties of final SiAlON ceramics. Processed β-Si3N4 powder characteristics are majorly investigated by SEM-EDX, XRD, XRF, laser particle sizer and elemental analyser. The existence of undesirable impurities in the β-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.
Highlights
SiAlON ceramic materials are ver y significant with their highly desirable, and proved potential, especially in industrial wear and high temperature applications 1-3)
TEL: +90-216-4839666 FAX: +90-216-4839118 processing stage has a strong effect on microstructural development, since ceramic parts are produced by the sintering of initial powder mixtures 8-12)
Removal of impurities from the raw powders, initial particle size distribution, homogeneous dispersion of sintering additives, and grinding of starting nonoxide powders are the important parameters in the microstructural formation of SiAlON materials with superior mechanical properties13-19)
Summary
SiAlON ceramic materials are ver y significant with their highly desirable, and proved potential, especially in industrial wear and high temperature applications 1-3). Removal of impurities from the raw powders, initial particle size distribution, homogeneous dispersion of sintering additives, and grinding of starting nonoxide powders are the important parameters in the microstructural formation of SiAlON materials with superior mechanical properties). SiAlON production processes are based on homogenization of raw powders α or β-Si3N4 powder, Al2O3, AlN and sintering additives such as Y2O3, Sm2O3, Er2O3, Dy2O3, CaO, etc. Free silicon and iron may originate from milling of the raw β-Si3N4 powder Removal of these impurities and/or achieving desired final phases including these impurities in the sintered product is required. Besides milling and sintering process parameters have crucial effects on microstructural evolution. In this respect, SiAlON powder processing technology involves a number of knowhow developments to produce materials with superior properties at low cost. The pellets were sintered both by gas pressure sintering (KCE, FPW 100/150-2200-25 type furnace), under 2.2 MPa nitrogen gas in a stanInitial β-Si3N4 Powder
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