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

Abstract

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.