Solid state reactions between Ni₃Al and SiC

Solid state reactions between SiC and Ni₃Al were studied at 1000 °C for different times. Multi-reaction-layers were generated in the interdiffusion zone. Cross-sectional views of the reaction zones show the presence of three distinguishable layers. The Ni₃Al terminal component is followed by NiAl, Ni_5.4Al₁Si₂, Ni_(5.4−x)Al₁Si₂ + C layers, and the SiC terminal component. The Ni_5.4Al₁Si₂ layer shows carbon precipitation free, while modulated carbon bands were formed in the Ni_(5.4−x)Al₁Si₂ + C layer. The NiAl layer shows dramatic contrast difference with respect to the Ni₃Al and Ni_5.4Al₁Si₂ layers, and is bounded by the Ni₃Al/NiAl and Ni_5.4Al₁Si₂/NiAl phase boundaries. The kinetics of the NiAl formation is limited by diffusion, and the growth rate constant is measured to be 2 × 10⁻¹⁰ cm²/s. The thickness of the reaction zone on the SiC side is always thinner than that on the Ni₃Al side and no parabolic growth rate is obeyed, suggesting that the decomposition of the SiC may be a rate limiting step for the SiC/Ni₃Al reactions. The carbon precipitates were found to exist in either a disordered or partially ordered (graphitic) state, depending upon their locations from the SiC interface. The formation of NiAl phase is discussed based on an Al-rejection model, as a result of a prior formation of Ni-Al-Si ternary phase. A thermodynamic driving force for the SiC/Ni₃Al reactions is suggested. © 1990, Materials Research Society. All rights reserved.