The Kinetics and Morphological Development of the Oxide Scale on Nickel-Iron Alloys (0–25 w/o Fe) at 1000°C

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Abstract
The oxidation kinetics were determined for nickel alloys containing 0–25 w/o (weight per cent) iron in oxygen at 1000°C. The kinetics, which were obtained for periods up to 100 hr, followed a parabolic relationship at long times. The parabolic rate constant was obtained as a function of alloy composition; it increased in magnitude with addition of iron up to 5 w/o and subsequently decreased to a value approximately equal to that for pure nickel. The external scale on alloys containing up to 2 w/o iron was virtually single‐phase nickel oxide. All other alloys exhibited scales consisting of an inner nickel oxide layer and an outer two‐phase nickel oxide‐spinel layer. All alloys oxidized internally, the internal oxide being an iron‐nickel spinel, . Iron preferentially concentrated in the oxide phases. There was a large degree of iron depletion in the alloy towards the alloy/oxide interface where the iron concentration was less than 1 w/o. A schematic model based on thermodynamic and diffusion properties is advanced to account for the observed variation of the parabolic constant with alloy composition.

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