Study On The Properties Of SiC Composite Materials Prepared By Carbonization And Nitriding

SiC refractories are widely used in metallurgy, machinery, chemical and other industries with excellent properties such as high strength, good thermal shock resistance, wear and corrosion resistance, etc. At the present, the industrial production of Si₃N₄-SiC and Sialon-SiC are generally have high cost of production and energy using which have limited their large-scale use. Si/β-SiC/Si₂N₂O/SiO₂-SiC composites were produced by Si powders and SiC particles as the raw material, adopting the method of semi-dry process, sintering buried in carbon particles at 1400℃and 1500℃. Phase composition, microstructure and micro-component of the samples were tested by XRD, SEM and EDS. And the relations of their phase composition and microstructure to the sintering performance, mechanical properties, thermal shock resistance, resistance to erosion and blast furnace slag were studied. The influence of Si powders content and sintering temperature on the properties of the composites were mainly discussed.The research showed that when adding 10%⁵0% Si powder to SiC particle and then buried in carbon particles sintering at 1400℃and 1500℃, the primary phase wereα-SiC,β-SiC,SiO₂,Si₂N₂O and Si. There were large amounts of acicular SiC fibers at both the surface and fracture of sample. Meanwhile platelike Si₂N₂O and some residual Si were discovered inside the sample. Research found that as the content of Si powder increased, both the bulk density and modulus of rupture of the sintered sample increased first and then decreased, and the samples with 25% Si powder had the biggest bulk density and best mechanic properties. They were 2.45g/cm³ and 96.85MPa respectively when sintering temperature was 1400℃, and as the sintering temperature was up to 1500℃, they were 2.34g/cm³ and 83.90MPa. The samples sintered at 1400℃were with higher mechanical properties and bulk density was mainly because that the residual Si they had. Experiment indicated that the existence of residual Si was helpful to the increase of the strength. Thermal shock experiment was done atâ–³T =1200℃, and the result showed that the samples with 25% Si powder had the best thermal shock resistance. Under the same experimental conditions, the modulus of rupture of the samples sintered at 1400℃were higher than that sintered at 1500℃after thermal shock. Their modulus of rupture of the samples with 25% Si powder sintered at 1400℃was 68.78MPa after thermal shock, which was its 71.01% of previous strength. Analysis believed that the numerous acicular SiC fibers, platelike Si₂N₂O and small residual Si crystal grains contributed to the improvement of the thermal shock resistance. We corroded the samples with cryolite and blast furnace slag, and the result showed that samples with content of Si powder higher than 25% all had good resistance to the cryolite and blast furnace slag. The corrosion layer was very thin, and dense protection layer was formed at the edge of the corrosion layer.