Electroplating has been widely used to synthesize nanocrystalline (nc) metals and alloys with grain sizes smaller than 100 nm. Because these nc metals and alloys possess nearly full density, narrow grain size distribution and controllable composition, they have been used extensively as paradigms for understanding the intrinsic mechanical properties of nc materials. However, it has been recognized that impurities from electrolyte and additives cannot be completely excluded during electroplating. These impurities can more or less transport into the deposited nc materials by surface adsorption and thereby influence the properties of the electroplated materials. However, quantitative measurements on the distributions of alloying elements and impurities in electroplated nc metals have not been reported before. In this study, atom probe tomography was employed to investigate atomic-scale element distributions in an electroplated nanocrystalline Ni alloy. Quantitative characterization evidences that weak yet detectable grain boundary segregations of carbon and cobalt occur during low-temperature electroplating (shown in Figure 1). Nanoindentation measurements suggest that the hardness of the alloy is ～1 GPa higher than that of the nanocrystalline pure Ni with the same grain size (shown in Figure 2). Classical solid solution strengthening cannot completely account for the hardness increment and hence the grain boundary segregations appear to play an important role in the strength improvement.
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