Article Dans Une Revue Oxidation of Metals Année : 2020

Growth Kinetics and Characterization of Chromia Scales Formed on Ni–30Cr Alloy in Impure Argon at 700 °C

Résumé

The oxidation of a Ni–30Cr alloy at 700 °C in impure argon was studied in order to provide new elements of understanding on chromia scale growth in low oxygen partial pressure atmosphere (10−5 atm). Oxidation tests were carried out during 30 min to 50 h in a thermogravimetric analysis system using a symmetrical balance with in situ monitoring of the oxygen partial pressure. The oxidation kinetics were determined as parabolic with an estimated stationary parabolic constant value of 10−15 cm2 s−1, after a transient stage of about 3 h. The oxide scale was identified as a pure chromia layer by TEM and XPS characterisations. After 50 h at 700 °C, the scale thickness estimated by TEM cross section observation was about 100 nm. A slightly thicker and more porous oxide scale was observed above the alloy’s grain boundaries. The metal/oxide interface also exhibited a deeper recession towards the substrate above the alloy’s grain boundaries. The orientation of chromia grains was determined by TKD (transmission Kikuchi diffraction). A strong preference was noted for the orientation perpendicular to the surface, along the < 0001 > direction of the corundum structure. Finally, the type of semiconduction was determined for the scales formed after 7 h and 50 h of oxidation. For the shorter oxidation time, the chromia scale exhibited an n-type semiconduction, whereas for the longer exposure, both n-type and insulating semiconduction were identified.

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hal-02995654 , version 1 (09-11-2020)

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Léa Bataillou, Laure Martinelli, Clara Desgranges, Sophie Bosonnet, Kevin Ginestar, et al.. Growth Kinetics and Characterization of Chromia Scales Formed on Ni–30Cr Alloy in Impure Argon at 700 °C. Oxidation of Metals, 2020, 93 (3-4), pp.329-353. ⟨10.1007/s11085-020-09958-7⟩. ⟨hal-02995654⟩
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