The air oxidation of a nanocrystalline Cu–10 wt%Ni alloy at 800°C

Abstract

The air oxidation of two copper-base Cu–Ni alloys having the same overall composition, but prepared by different methods and presenting widely different grain sizes, has been carried out at 800°C to examine the effect of a large reduction in the grain size on the oxidation behavior of a solid-solution alloy. Both alloys formed an external scale of copper oxide (CuO+Cu 2O) plus a region of internal oxidation of nickel. However, the overall oxidation rate of the alloy with a grain size in the nanometer range was faster and the depth of internal oxidation was larger than those measured for the conventional alloy under the same conditions. Moreover, the particles of nickel oxide (NiO) formed by internal oxidation were present only in the alloy-consumption region for the conventional alloy, while for the mechanical alloy they were distributed throughout the whole thickness of the external scale. These differences were attributed to a faster transport of oxygen in the alloy and of oxygen and copper in the scales for the fine-grained material resulting from a decrease of the grain size both in the alloy and in the scale and from a concomitant increase in the effective diffusion coefficients of the relevant species.