Microstructure And Properties Of α-Sialon/SiC Composites Synthesized From Water Quenched Blast Furnace Slag

Sialon/SiC composite is a promising material for its high strength, good wear resistance and high chemical stability. It has been widely used in various fields, such as mechanical, chemical, metallurgical and other industries. However, the widespread application of Sialon/SiC composite has been restricted by the difficult synthesis of Sialon powder. Therefore, further studies should be made for this issue. Water quenched blast furnace slag consists of SiO2、Al2O3、CaO and some impurities including Fe, which is a suitable raw material for preparing Sialon powder. This study is focused on synthesizing low-cost a-Sialon/SiC composite with good properties by using a-Sialon powder mentioned above.The a-Sialon/SiC composite was synthesized by pressureless sintering technique. The Ca-a-Sialon powder derived from water quenched blast furnace slag and SiC were used as raw materials. In this study, the effect of SiC content on the sintering character, microstructure, mechanical properties and oxidation resistance of the a-Sialon/SiC composite was investigated. The phase identification, grain size, fracture mode, oxidation mechanism, strengthening and toughening mechanism of a-Sialon/SiC composite were also investigated by means of X-ray diffraction (XRD), scanning electron microscope (SEM), and the thermodynamic analyses.The experimental results showed that main phases of the composite after sintering were a-Sialon and SiC. The amount of columnar grains in a-Sialon/SiC composite decreased and the grain size became smaller with increasing the SiC content.The addition of SiC could promote densification and improve the mechanical properties of the composite. However, the mechanical properties decreased when the SiC content was more than10wt%. The a-Sialon/SiC composite with10wt%SiC showed the optimized properties. The volume density, bend strength, fracture toughness and Vickers-hardness of that were3.26g·cm-3,355MPa,5.5MPa·m-1/2and17.7GPa, respectively. The oxidation experiments showed that a-Sialon/SiC composite exhibited excellent oxidation resistance. The oxidation resistance enhanced with increasing the SiC content. The oxidation behavior followed with a parabolicrate law. The oxidation mass gain of the composite with different SiC content after oxidation at1200℃for40h was varied between0.29mg·cm-2and1.20mg·cm-2. The oxidation activation energy of the composite increased with increasing the SiC content. The oxidation activation energy of α-Sialon without SiC was79kJ/mol, while it was219kJ/mol for the a-Sialon/SiC composite with10wt%SiC. With the increase of oxidation temperature, oxidation products were changed because of Y3+and Ca2+diffusion into the oxide layer. The oxidation products after oxidation at1200℃were SiO2(cristobalite), Y2Si2O7and CaAl2Si2O8(anorthite). Furthermore, the a-Sialon/SiC composite material also showed good thermal shock performance. The thermal shock resistance enhanced with increasing the SiC content.