Microstructural Evolution in Liquid‐Phase‐Sintered SiC: Part III, Effect of Nitrogen‐Gas Sintering Atmosphere

摘要: Effects of N 2 sintering atmosphere and the starting SiC powder on microstructural evolution liquid-phase-sintered (LPS) were studied. It was found that, for β-SiC case, there complete suppression β → α phase transformation, which otherwise goes to completion in Ar atmosphere. also that microstructures equiaxed coarsening severely retarded, contrast with Ar-atmosphere case. Chemical analyses specimens sintered revealed presence significant amounts nitrogen, believed reside mostly intergranular phase. argued nitrogen LPS helped stabilize phase, thereby preventing transformation attendant formation elongated grains. To investigate retardation, internal friction measurements performed either or For atmosphere, a remarkable shift grain-boundary sliding relaxation peak toward higher temperatures very high activation energy values observed, possibly due incorporation into structure liquid The highly refractory viscous nature deemed responsible retarding solution-reprecipitation these materials. Parallel experiments using α-SiC powders further reinforce arguments. Thus, processing open possibility tailoring their room-temperature mechanical properties making high-temperature materials are resistant creep.