Dynamic oxidation behavior of TD-NiCr alloy with different surface pretreatments

  • C. T. Young
  • D. R. Tenney
  • H. W. Herring


Oxidation tests of TD-NiCr alloy with different surface pretreatments were conducted in a Mach-5 arc-jet at 1200°C and 0.002 lb/s flowing air environment. Extensive scanning electron microscopy and X-ray analyses were carried out to determine the mechanisms responsible for the observed oxidation behavior. The presence of atomic oxygen in the air stream plays a significant role in determining the oxidation characteristic of the alloy. The rate of Cr2O3 vaporization by formation of volatile CrO3 is greatly enhanced by the flowing conditions. The typical microstructure of oxides formed in the dynamic tests consists of an external layer of NiO with a porous “mushroom”-type morphology, an intermediate layer of NiO and Cr2O3 oxide mixture, and a continuous inner layer of Cr2O3 in contact with the Cr-depleted alloy substrate. The formation of mushroom-type NiO is attributed to three basic processes: 1) vaporization of NiO by dissociation into its elements, 2) reoxidation of Ni vapor predominantly with atomic oxygen, and 3) condensation of NiO at elevated sites on the specimen surface. The oxidation rate is determined by the rate of vaporization of NiO. Surface pretreatment has a significant effect on the oxidation behavior of the alloy in the early stage of oxidation, but becomes less important as exposure time increases. Mechanical polishing induces surface recrystallization, which enhances the formation of Cr2O3 in static environment, but promotes the concurrence of external growth of NiO and internal oxidation of the alloy in the dynamic atmosphere.


Metallurgical Transaction Oxide Morphology Dynamic Oxidation External Growth Duplex Oxide 
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Copyright information

© The Minerals, Metals & Materials Society - ASM International - The Materials Information Society 1975

Authors and Affiliations

  • C. T. Young
    • 1
  • D. R. Tenney
    • 2
  • H. W. Herring
    • 3
  1. 1.Bendix Research LaboratoriesThe Bendix CorporationSouthfield
  2. 2.NASA-Langley Research CenterHampton
  3. 3.NASA-Marshall Flight CenterHuntsville

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