Oxidation kinetics of Cu-30vol.%Cr coating

Chiang, K.T.; Ampaya, J.P.

doi:10.1016/0257-8972(95)02421-2

“…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.…”

Section: The Oxidesmentioning

confidence: 77%

“…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.…”

mentioning

confidence: 99%

“…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.…”

mentioning

confidence: 99%

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

Thomas‐Ogbuji

¹

,

Gray²

2004

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Oxidation kinetics of Cu-8Cr-4Nb was investigated by TGA exposures between 500 and 900°C (at 25-50°C intervals) and the oxide scale morphologies examined by microscopy and micro-analysis. Because Cu-8Cr-4Nh is comprised of fine Cr2Nb precipitates in a Cu matrix, the results were interpreted by comparison with the behavior of copper (OFRC) and "NARloy-Z" (a rival candidate material for thmst cell liner applications in advanced rocket engines) under the same conditions. While NARloy-Z and Cu exhibited identical oxidation behavior, Cu-8Cr-4Nb differed markedly in several respects: below ~ 700°C its oxidation rates were significantly lower than those of Cu; At higher temperatures its oxidation rates fell into two categories: an initial rate exceeding that of Cu, and a terminal rate comparable to that of Cu. Differences in oxide morphologies paralleled the kinetic differences at higher temperature: While NARloy-Z and Cu produced a uniform oxide scale of CU20 inner layer and CuO outer layer, the inner (CU20) layer on Cu-8Cr-4Nb was stratified, with a highly porous/spongy inner stratum (responsible for the fast initial kinetics) and a dense/blocky outer stratum (corresponding to the slow terminal kinetics). Single and spinel oxides ofNb and Cr were found at the interface between the oxide scale and Cu-8Cr-4Nb substrate and it appears that these oxides were responsible for its suppressed oxidation rates at the intermediate temperatures. No difference was found between Cu-8Cr-4Nb oxidation in air and in oxygen at 1.0 atm.

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“…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.…”

Section: The Oxidesmentioning

confidence: 99%

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

Ogbuji¹

2004

Materials at High Temperatures

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Oxidation kinetics of Cu-8Cr-4Nb was investigated by TGA exposures between 500 and 900°C (at 25-50°C intervals) and the oxide scale morphologies examined by microscopy and micro-analysis. Because Cu-8Cr-4Nh is comprised of fine Cr2Nb precipitates in a Cu matrix, the results were interpreted by comparison with the behavior of copper (OFRC) and "NARloy-Z" (a rival candidate material for thmst cell liner applications in advanced rocket engines) under the same conditions. While NARloy-Z and Cu exhibited identical oxidation behavior, Cu-8Cr-4Nb differed markedly in several respects: below ~ 700°C its oxidation rates were significantly lower than those of Cu; At higher temperatures its oxidation rates fell into two categories: an initial rate exceeding that of Cu, and a terminal rate comparable to that of Cu. Differences in oxide morphologies paralleled the kinetic differences at higher temperature: While NARloy-Z and Cu produced a uniform oxide scale of CU20 inner layer and CuO outer layer, the inner (CU20) layer on Cu-8Cr-4Nb was stratified, with a highly porous/spongy inner stratum (responsible for the fast initial kinetics) and a dense/blocky outer stratum (corresponding to the slow terminal kinetics). Single and spinel oxides ofNb and Cr were found at the interface between the oxide scale and Cu-8Cr-4Nb substrate and it appears that these oxides were responsible for its suppressed oxidation rates at the intermediate temperatures. No difference was found between Cu-8Cr-4Nb oxidation in air and in oxygen at 1.0 atm.

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“…In addition, the use of a suitable top coat to act as a thermal barrier can allow the engine to run at higher temperatures thereby resulting in its increased thermal efficiency. As a result, several types of ceramic [1,5] and metallic [10,11,12,13,14,15] coatings have been advocated as protective coatings for copper alloy liners. However, differences in the mechanical and thermophysical properties between the coatings and copper alloy substrates can lead to the development of large residual stresses and coating spallation as the coated liner experiences variations in temperature during processing and engine operation [16].…”

Section: Introductionmentioning

confidence: 99%