High temperature corrosion of nanocrystalline three-phase Cu-20Ag-20Cr bulk alloy

• When grain size is refined, the corrosion rates of Cu-20Ag-20Cr alloy become higher at 600–700 °C, but lower at 800 °C.
• Coarse-grained Cu-20Ag-20Cr alloy is unable to form the scales of chromia.
• Nanocrystalline Cu-20Ag-20Cr alloy is also unable to form the scales of chromia at 600 °C.
• Nanocrystalline Cu-20Ag-20Cr alloy is able to form a bright and continuous layer of Ag2O at 700 °C.
• Nanocrystalline Cu-20Ag-20Cr alloy is able to form an irregular and continuous layer of chromia at 800 °C.

High temperature corrosion of nanocrystalline MACu-20Ag-20Cr(at.%) alloy prepared by mechanical alloying(MA) was studied as compared with that of coarse grained PMCu-20Ag-20Cr alloy prepared by powder metallurgy(PM). PMCu-20Ag-20Cr alloy forms an external layer composed of CuO or CuO and CuCr2O4, while the internal layer is composed of alloys as well as Cu, Ag and Cr oxides. MACu-20Ag-20Cr alloy forms the same scale structures as PMCu-20Ag-20Cr alloy at 600 °C. On the contrary, it forms a bright layer of Ag2O at 700 °C, but an irregular and continuous layer of chromia at 800 °C, which prevent the alloy from being oxidized further.

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