Fe-30Ni合金表面酸化皮膜の成長と深さ方向の組成分布

抄録

Fe-30 Ni alloy samples were oxidized for 10 to 240 minutes at 433 to 473K under a pure oxygen pressure of 1.33×10⁴Pa. The thickness of oxide films was measured by a multiple-angle incidence ellipsometer. The kinetics of film growth was found to obey a parabolic rate law. The depth-profiling of oxidized surfaces, performed with simultaneous use of Auger electron spectroscopy (AES) and argon ion sputter-etching technique, reveals that the iron component is preferentially oxidized, producing a nickel-enrichment zone in the alloy side of the film/alloy interface.
As the oxidation time or the oxidation temperature increases, the nickel-enrichment zone tickens, whereas the concentration gradient in the nickel-enrichment zone decreases. During oxidation of the alloy, the rate of transport of iron component in the film was almost equal to the interdiffusion rate in the substrate alloy, indicating a steady-state. The apparent value of interdiffusion coefficient, D estimated at the steady-state is 7.3×10^-16cm²·s^-1 at 473K, which is more than ten orders of magnitude higher than the value extrapolated from the lattice-diffusion data obtained at high temperature. The large value of D may be explained in terms of the divacancy-enhanced lattice diffusion mechanism rather than the grain boundary diffusion mechanism.