The third-element effect in the oxidation of Ni–xCr–7Al (x = 0, 5, 10, 15 at.%) alloys in 1 atm O2 at 900–1000 °C |
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Authors: | Y Niu XJ Zhang Y Wu F Gesmundo |
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Affiliation: | aState Key Laboratory for Corrosion and Protection, Institute of Metal Research, Chinese Academy of Science, Wencui Road 62, 110016 Shenyang, China;bShenyang Institute of Chemical Technology, 110142 Shenyang, China;cDICheP – Università di Genova, Fiera del Mare, Pad.D, 16129 Genova, Italy |
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Abstract: | The oxidation in 1 atm of pure oxygen of Ni–Cr–Al alloys with a constant aluminum content of 7 at.% and containing 5, 10 and 15 at.% Cr was studied at 900 and 1000 °C and compared to the behavior of the corresponding binary Ni–Al alloy (Ni–7Al). A dense external scale of NiO overlying a zone of internal oxide precipitates formed on Ni–7Al and Ni–5Cr–7Al at both temperatures. Conversely, an external Al2O3 layer formed on Ni–10Cr–7Al at both temperatures and on Ni–15Cr–7Al at 900 °C, while the scales grown initially on Ni–15Cr–7Al at 1000 °C were more complex, but eventually developed an innermost protective alumina layer. Thus, the addition of sufficient chromium levels to Ni–7Al produced a classical third-element effect, inducing the transition between internal and external oxidation of aluminum. This effect is interpreted on the basis of an extension to ternary alloys of a criterion first proposed by Wagner for the transition between internal and external oxidation of the most reactive component in binary alloys. |
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Keywords: | Ternary alloys Ni– Cr– Al Oxidation Third-element effect |
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