Coatings of Nb-based Alloy by Cr and/or Al Pack Cementations and Its Oxidation Behavior in Air at 1273–1473K

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 1473K 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 -Cr and inner Cr2Nb layer, and showed good oxidation resistance up to 1373K. The alloy packed with Cr and then Al formed a coating layer with outermost -Cr(Al), outer -Cr(Nb), and inner Cr2Nb layers, and this coated alloy showed good oxidation resistance up to 1473K by forming an Al2O3 scale