| Silicon nitride bonded silicon carbide materials consist of silicon carbide as the main phase and silicon nitride as bonded phase, which have excellent properties such as great high temperature strength, high thermal conductivity, good thermal shock resistance, high softening point load, low thermal expansivity, splendid resistance to high temperature creep and acid as well as not wetting by non-ferrous metals and desirable oxidation resistance.. Its operating temperature can be up to1500℃in kinds of atmospheres, and it was used to ceramic sanitary ware, domestic ceramics, electronic ceramic, art porcelain ceramic, grinding wheel, abrasive tool and metallurgy industry, etc. can effectively reduce the energy consumption, reduce defects products, improve the quality of products.This paper by SiC, Si as the main raw material, add appropriate sintering additives and binder was molded by general repression, the greenbody was further compaction by the method of static pressure. Finally, the greenbody was sintered in the N2atmosphere. The influence of firing system, different particle sizes of SiC powder and sintering additives on Si3N4/SiC composite ceramic were studied by the SEM and XRD analysis. And the results are as follows:The firing process is divided into two stages. The first stage is heat preservation at low temperature and the second is heat preservation at high temperature. The time of heat preservation longer, the content of a-Si3N4of the sample more, but the content of β-Si3N4less, The performances of sample a-Si3N4/β-Si3N4after sintering at high temperature were best with lowest apparent porosity, highest volume density and highest crushing strength when the heat preservation was1hour at low temperature. During the stage of heat preservation at high temperature, with the preservation temperature increased, the apparent porosity was decreased and the volume density and crushing strength were increased at first, and then decreased at first and then was increased was increased and the volume density and crushing strength were decreased. The apparent porosity was lowest, the volume density and crushing strength were largest when the preservation temperature was up to1550℃. The optimal sintering system for the sample was that the time of heat preservation at low temperature(1350℃) was1hour, but at high temperature(1550℃) was3hours.Aiming at SiC materials in different particle size, the results showed that, with a single particle size as the research object, finer the particle size of SiC is, the sintering performance of sample is better, and the crushing strength is greater, when SiC particle size is0.5um, the strength of sample is biggest, as275MPa; with different gradation materials as the object of study, when addition of SiC fine powder(0.5μm) is35%, addition of SiC fine powder (325mesh) is10%, addtion of SiC fine powder (200mesh) is5%, various aspects of performance of sample achieve best value; the performance of sample with different gradation fine powder as raw materials is better than with single particle size as raw materials.We slelect Y2O3power, magnesium-alumina spinel, talc power, α-Al2O3power and ZrO2power as sintering additives, research results show that, sintering additives had important effect for Si3N4combination SiC composite ceramic, they can react with SiO2and Si3N4in high temperature generating low melting point phases, one side they can promote the sintering of sample, on the other hand, they can pomote change a-Si3N4to (3-Si3N4, decreasing in a-Si3N4production, both too much or too little a-Si3N4is adverse on sintering, difficult to close packing on sample, when we use the Y2O3power as sintering additives, the smaples we got have low apparent porosity, high volume density and compressive strength, also have the optimal sintering performance. |
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