Fabrication And Properties Of Silicon Nitride Bonded Silicon Carbide By Reaction Sintering

Reaction sintering was applied into fabrication of silicon nitride bonded silicon carbide because of simple prinicple, controlled process parameters and perfect sample dimenison precission, etc. However, its industrial application was hindered by long reaction period and low effecience. There is a way to accelerate reaction speed and improve densification behavior and mechanical performance by adding additives. In this thesis, silicon nitride bonded silicon carbide was prepared by "stage-temperature" reaction sintering when SiC powder, Si powder as raw materials, and ZrO₂, Y₂O₃, Al₂O₃ as sintering additives, and Al,α-Si₃N₄ as inducer. Archimedes' method was applied to analyze sintering properties, including bulk density, apparent porosity and hygroscopic coefficient. Flexural strength was evaluated by three-point bending test. Thermal shock resistance was obtained by water quenching method. Phases of reaction products and fracture microstrcture were determinded by XRD and SEM.Sample with coarse SiC powder and more additives has the better combination properities through orthogonal design experiment. Densification and flexural strength was deteriorated when particle size of SiC decreased because more liquid phase easily leads to block diffusion of nitrogen. The most appreciate final sintering temperature was obtained by process experiment. Densification and flexural strenghth are fitted to parabola model as sintering temperature increased. The most appreciated amount of mixed rare-earth oxidation was determinded by additives experiment. As a result, adding more additives simply can't improve densification and mechanical performance. Finally, the sintering mechanism of silicon nitride was explored by XRD and SEM, which is solution- reprecipitation mechanism.