Study On Gelcasting Of Reaction-bonded Silicon Carbide And Properties Of Sintered Ceramics

In order to fabricate homogenous silicon carbide components with large dimensions and complex shapes, gelcasting technique was employed to form silicon carbide/carbon (SiC/C) green bodies, and then the green bodies were reacted with liquid silicon to make reaction-bonded silicon carbide (RBSC) ceramics. In this paper, preparation of SiC/carbon black slurries with low viscosity and high solid loading, uniform consolidation of SiC/carbon black slurries, and the properties and microstructure of the green body and RBSC have been researched. The main contents and conclusions of the research were listed as below:(1) Three types of silicon carbide powders and tvo types of carbon black were used to make SiC/carbon black slurries with low viscosity and high solid loading. The effects of particle size of the SiC and carbon black powders on the rheological behavior of the slurries were investigated. It was fourd that it was difficult to prepare SiC/carbon black slurries with high solid loading only using one kind of silicon carbide powder. When two kinds of silicon carbide powders with different particle size distribution were mixed as starting materials, the viscosity of SiC/carbon black slurries decreased. At optimum condition, SiC/carbon black slurries with 70vol% solid loading were prepared. The slurry with viscosity of 1.6Pa S at the shear rate 50 S"1 showed good rheological behavior, and was suit able for gelcasting process.(2) Polymerization of the acrylamide monomer in the consolidation was deeply researched. Microwave heating consolidation, room-temperature consolidation and routine heating consolidation were used to realize ccnsolidation of SiC/carbon black slurries. It was found that uniform consolidation could be realized if the polymerization of the acrylamide monomer took place after the time when temperature equilibrium of the slurry was reached during routine heating consolidation process. Uniform consolidation provided the basis for fabricating homogenous silicon carbide components with large dimensions.(3) The effects of monomer concentration and ratio of MBAM/AM on the strength and shrinkage of the green bodies were studied. With the increase of monomer concentration or the increase of the ratio of MBAM/AM, the strength of the green body increased. The highest value of bending strength was 8 MPa and theshrinkage of the green body is below 1%. Samples with large dimensions and complex shapes were prepared.(4) The properties and microstructure of the green body and RBSC ceramics were investigated. The SEM photos of the samples indicated that both the green bodies made by gelcasting and the RBSC ceramics showed homogeneous microstructure. The weibull modulus of the RBSC ceramics was up to 12.05, and the mean bending strength was up to 367.69MPa. Through the analysis of the microstructure of RBSC, it was thought that the mechanism of reaction sintering process could be explained by the solution-precipitation theory.