Oxidation behavior of CuNb microcomposites

The general isothermal oxidation behavior of Cu–8Cr–4Nb

“…Oxidation of Cu-8Cr-4Nb seems to differ somewhat from that of the Cu-Cr and Cu-Nb alloys studied by' Chiang et al [7][8][9]. They suggested that the second phase (which was Cr or Nb) oxidizes in-situ in the Cu matrix.…”

“…9(a), and the EDS line scan along the dotted line is shown in Fig. 9 The Cll matrix in this material would be expected to oxidize in the same way as pure Cll, by outward diffusion of Cu + through the oxide scale as the rate limiting event [4]; and the precipitates probably react with oxygen that has diffused through the oxide scale to the substrate interface, in the manner proposed for Cu-Cr and Cu-Nb alloys [7][8][9]. Oxidation of the Cr2Nb precipitates best explains the enhanced oxidation resistance of Cu-8Cr-4Nb at intermediate temperatures, since these precipitates are the only point of difference from pure Cu.…”

“…of other Cr2Nb-containing alloys [11] and ofCu-Cr and Cu-Nb [7][8][9] give no indication that the Cr2Nb precipitates in Cu-8Cr-4Nb might confer any oxidative advantage. In any case, even the complete oxidation of the 8 at% Cr in this alloy would be insufficient to provide complete Cr203 coverage.…”

“…Chiang and co-workers have evaluated the oxidation resistance of Cu-Nb and Cu-Cr coatings proposed for rocket engine applications [7][8][9]. Using mini composites made by co-deposition of the elemental constituents from vapor phase or by sputtering, they found that: (1) Cu-Nb fonned a non-protective duplex scale, with the thickening of CuOlCu 2 0 at the surface controlled by outward diffusion of Cu, while inward diffusion of oxygen controlled the growth of a poorly consolidated subscale comprised of niobium oxides (Nb20S and CUNb206); (2) in Cu-Cr a Cr content of 15 -30 vol % was necessary to assure formation of a continuous and protective Cr203 top scale.…”

Comparison of the Isothermal Oxidation Behavior of As-Cast Cu–17%Cr and Cu–17%Cr–5%Al. Part II: Scale Microstructures

“…It was demonstrated that the addition of 5%Al to the Cu-17%Cr significantly improved its oxidation properties. In contrast to Cu-17%Cr, which exhibited parabolic oxidation behavior similar to pure Cu [1][2][3][4][5][6][7][8][9][10][11], Cu-Al [11][12][13], and several Cu-Cr [7,9] alloys, the oxidation behavior of Cu-17%Cr-5%Al is better represented by either a combination of parabolic and quartic equations or a logarithmic equation. The ternary phase diagrams [14,15], as well as the microstructural observations shown in Fig.…”