OXIDATION STUDIES OF CU-CR-COATED CU-NB MICROCOMPOSITE

The use of appropriate copper-based alloy coatings on structural compo nents offers an avenue to minimize high temperature oxidation and exte nd component life in an oxidizing environment. Cr2O3 Scales, similar t o those formed on M-Cr (M = Ni, Co, Fe), would provide oxidation resis tance for copper-based materials if they could form on a Cu-Cr coating system. In the present study, three Cu-Cr coating compositions, i.e. Cu-15vol.%Cr,Cu-30vol.%Cr and Cu-45vol.%Cr, were produced by codeposit ion of copper and chromium on Cu-15vol.%Nb substrates. The oxidation k inetics and oxide morphologies were characterized after exposure to ai r at 649-degrees-C. The oxidation products of the Cu-15vol.%Cr coating consisted primarily of copper oxides with discontinuous Cr2O3 scales. A transition from discontinuous to continuous Cr2O3 scale formation o ccurred between 15 and 30 vol.% Cr. For the Cu-30vol.%Cr and Cu-45vol. %Cr coatings, protective Cr2O3 scales were formed which markedly reduc ed the oxidation rates.