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Microstructure and growth kinetics of the fibrous composite subscale formed by internal oxidation of SmCo5

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Abstract

The oxidation of SmCo5 is an unusual example of selective internal oxidation in which the subscale formed consists of a composite microstructure containing samarium oxide fibers and β-cobalt. The oxide fiber size increases with oxidation temperature, and the orientation of the fibers is generally perpendicular to the subscale-alloy interface. The unusual structure results because of the high concentration of samarium in the intermetallic compound, coupled with a low solubility of samarium in metallic cobalt resulting in a subscale consisting of 39 vol pct oxide. Growth of the subscale follows the parabolic oxidation law, and the kinetics have been determined between 100 and 1125°C. The kinetics are too fast to be explained by lattice diffusion in either the oxide or the cobalt phases. Oxygen diffusion down the cobalt-oxide fiber interface appears to be the transport mechanism for this diffusion controlled process. The oxidation behavior of PrCo5 is identical with that of SmCo5.

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Authors and Affiliations

  1. Department of Applied Earth Sciences, Stanford University, 94305, Stanford, Calif.

    Robert W. Bartlett (Associate Professor, Process Metallurgy Group)

  2. Materials Laboratory, Stanford Research Institute, 94025, Menlo Park, Calif.

    Paul J. Jorgensen (Assistant Director)

Authors
  1. Robert W. Bartlett
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  2. Paul J. Jorgensen
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Bartlett, R.W., Jorgensen, P.J. Microstructure and growth kinetics of the fibrous composite subscale formed by internal oxidation of SmCo5. Metall Trans 5, 355–361 (1974). https://doi.org/10.1007/BF02644102

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  • DOI: https://doi.org/10.1007/BF02644102

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