Interfacial Solid State Reactions Of The SiC/Ni-Al Systems

The interfacial solid state reaction between SiC and various metals is one of the acute problems, when SiC is used in fabricating for high-temperature structural ceramics and metal matrix composites, etc. In this study, an all-around research aimming at the SiC/Ni-Al (NiAl, Ni₃Al) interfacial solid state reactions has been done to reveal the phenomena and regularities in the reations. They are the essential points for fabricating and using the SiC reinforced Ni-Al matrix composites and the SiC/Ni-Al alloy high-temprecture complexes.After the SiC/Ni-Al plane-interface couples annealed range from 1000℃to 1100℃for times from 5 to 15 hours, the reaction zones were detected using scaning electron microscope(SEM), energy disperse spectroscopy analyzer(EDS) and X-ray diffraction analyzer (XRD). The studies mainly focus on the morphologies, the microstructures and the elemental distributions of the reaction zone. The effects of the annealing temperature and time on them were also investigated. Meanwhile, the thermodynamic and kinetic analyses of the SiC/Ni-Al interfacial solid state reactions were carried out, too.After the SiC/Ni₃Al planar interface couple annealed at 1000℃for 5h, the results show that the reaction zone is composed of Ni₂Si, graphitic carbon precipitates and Ni_5.4AlSi₂. However, after the SiC/Ni₃Al planar interface couple annealed at 1100℃for 5h, the phase compositions of the reaction zone is changed to Ni_5.4AlSi₂, graphitic carbon and NiAl. The reaction zone is composed of two sublayers of random carbon precipitation zone (R-CPZ) and carbon precipitation free zone (C-PFZ). The R-CPZ, adjacent to the SiC terminal, is of Ni_5.4Al₁Si₂ matrix, in which the plate and sphere-like graphitic carbon precipitates are randomly distributed. The C-PFZ, adjacent to the Ni₃Al terminal, is of Ni_5.4AlSi₂ and NiAl without the graphitic carbon precipitates.The formation of the SiC/Ni-Al interfacial solid state reaction zones was analyzed in terms of the thermodynamic calculations. And a model of the SiC/Ni₃Al interfacial solid state reaction was established. The reaction follows the parabolic growth mechatism, indicating the diffusion controlled reaction kinetics. The kinetic function of the SiC/Ni₃Al interfacial solid state reaction is described: K=1.9×10^-3exp(-213×10³/RT), m²/s.The SiC/Ni₃Al interfacial solid state reaction is controlled by the the lattice diffusion and grain boundary diffusion of Ni in Ni_5.4AlSi₂. The SiC/NiAl composite system has much higher chemical compatibility than the SiC/Ni₃Al composite system, because no reaction was detected in the SiC/NiAl planar interface couple on the same annealing conditions as for the the SiC/Ni₃Al one.