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An Nb–5Mo–15W alloy (mass%) was surface-treated in vacuum by Cr and/or Al pack cementations, and the oxidation behavior of the coated alloys was investigated in air at temperatures up to 1473 K for 32.4 ks. The Al packed alloy formed a coating layer with the outer NbAl2 and the inner Nb3Al, and showed poor oxidation resistance. The Cr packed alloy formed a coating with outer α-Cr and inner Cr2Nb layer, and showed good oxidation resistance up to 1373 K. The alloy packed with Cr and then Al formed a coating layer with outermost α-Cr(Al), outer α-Cr(Nb), and inner Cr2Nb layers, and this coated alloy showed good oxidation resistance up to 1473 K by forming an Al2O3 scale.
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Fukumoto et al. (2003) studied this question.
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