Studies On The Interfacial Solid State Reaction Of SiC/Fe-Al Intermetallic Compounds

It is well known that SiC is the typical high temperature structural ceramic material, and Fe-Al intermetallic compounds (Fe₃Al, FeAl) own higher toughness, reliability and machinability than most of ceramics. The SiC/Fe-Al intermetallic compound complexes and the SiC/Fe-Al intermetallic compound composites have great potential applications in the aeronautic and astronautic areas. Study on the intherfacial solid state reactions between SiC and the Fe-Al intermetallic compounds is important theoretically and practically, however, it is not systematically reported so far, to the author's knowledge. In the current study, the interfacial solid state reactions of SiC/Fe-Al intermetallic compounds were investigated, especially on the phase compositions and microstructures of the reaction zones, the reaction kinetics and the reaction mechanisms. The conclusions are believed to provide valuable data for the developing the SiC/Fe-Al intermetallic compound complexes and the SiC/Fe-Al intermetallic compound composites.This paper focuses on the interfacial solid state reaction of the SiC/Fe-Al intermetallic compound planar couples after annealing at different temperatures for various times. The morphologies, microstructures and phase compositions of the reaction zone were mainly studied using scanning electron microscope (SEM) with energy disperse spectroscopy analyzer (EDS) and X-ray diffraction (XRD). Meanwhile, the effect of the heat treatment on the interfacial reaction was also investigated. Finally, the kinetics of the reaction was determined, and a schematic model was established to explain the interfacial solid state reaction between SiC and Fe₃Al.Summarily, the reaction zone of the SiC/Fe₃Al couples is composed of Fe₃Si, graphitic carbon precipitates and the Fe-Si-Al ternary compounds (FeSiAl₅ and FeSi₃Al₉). When annealing at 1050℃for 10 hours, the reaction between SiC and Fe₃Al is considerable with a thickness of about 128μm. The reaction zone is consisted of the band structure, i.e. the modulated carbon precipitation zone (M-CPZ) and the random carbon precipitation zone (R-CPZ) from the SiC terminal to the Fe₃Al terminal. The formation of the M-CPZ results from the discontinuous decomposition of SiC. On the contrary, the reaction between SiC and Fe₃Al in the temperatures below 1000℃is rather weak, indicating a high chemical compatibility of the SiC/Fe₃Al couple.After annealing at the same temperature of 1050℃for 20 hours, the reaction zone of the SiC/FeAl couple is only about several microns in thickness, which is much smaller than that of the SiC/Fe₃Al couple. It is due to the restraining effect of aluminium on reactive activity of the Fe-Al alloys. In other words, the reactive activity of the Fe-Al alloys decreases with increasing the Al content in them. So, in the case of the SiC/FeAl couple, the interfacial reaction is weaker with a thinner reaction zone thickness, compared with that in the SiC/Fe₃Al couples.The reaction kinetics of the interfacial solid state reaction between SiC and Fe₃Al was determined to be a parabolic rate, indicating a diffusion-controlled function. The reaction rate constant, K, can be described as K=1.6×10^-4exp(-217×10³/RT), m²/s. The diffusion of Fe in the reaction zone of the SiC/Fe₃Al couple should be the reaction rate controlled species.