Oxidation Mechanism of Ni—20Cr Foils and Its Relation to the Oxide-Scale Microstructure |
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Authors: | Calvarin G Molins R Huntz A M |
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Affiliation: | (1) LEMHE, CNRS, UMR 8647, Université Paris XI, 91405 Orsay, France;(2) ENSMP, UMR CNRS 7633, Centre des Matériaux, 91003 Evry, France |
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Abstract: | The oxidation behavior of Ni—20Cr foils of 100- and 200-m thickness wasstudied in air between 500 and 900°C. Simultaneously, the morphology,microstructure, and composition of the oxide layers were determined byscanning and transmission electron microscopies. Depending on thetemperature, the oxide layer differed significantly. The scale formedat all temperatures was complex, with an outer NiO layer having columnargrains, and an inner layer of equiaxedNiCr2O4+NiO+Cr2O3 grains. At low temperatures (500 and 600°C),the chromium content was insufficient to form a continuousCr2O3 layer, while such a continuous layer formed at theinner interface at oxidation temperatures of 700 to 900°C. At 600°C,internal oxidation of chromium occurred in the substrate. The oxidationmechanism is described taking into account these morphologies and theoxidation kinetics. The observation of no significant differences betweenthe oxidation behavior of thin strips and thick materials is related to thelimited exposure times of the study. |
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Keywords: | Oxidation mechanism Ni— Cr foils NiO Cr2O3 electron microscopy |
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