Solute distribution in nanocrystalline Ni–W alloys examined through atom probe tomography

Abstract

Abstract Atom probe tomography is used to observe the solute distribution in electrodeposited nanocrystalline Ni–W alloys with three different grain sizes (3, 10 and 20 nm) and the results are compared with atomistic computer simulations. The presence of grain boundary segregation is confirmed by detailed analysis of composition fluctuations in both experimental and simulated structures, and its extent quantified by a frequency distribution analysis. In contrast to other nanocrystalline alloys previously examined by atom probe tomography, such as Ni–P, the present nanocrystalline Ni–W alloys exhibit only a subtle amount of solute segregation to the intergranular regions. Acknowledgements This work was supported by the US Army Research Office under contract DAAD19-03-1-0235; the views presented herein are not endorsed by the sponsor. Research at the Oak Ridge National Laboratory SHaRE User Facility was sponsored by the Office of Basic Energy Sciences, US Department of Energy, under contract DE-AC05-00OR22725 with UT–Battelle, LLC. The authors would like to thank Dr Alan Lund (MIT) for providing the simulation structure, Megan Frary for assisting in the preparation of figure 1, K. F. Russell for help with atom probe specimen preparation and Oxford nanoScience Ltd. for use of their Position Sensitive Atom Probe (PoSAP) software. Notes † In an effort to better match the density and resolution of the atom probe data, we have also considered simulated structures in which 40% of the atoms were removed at random, or in which the atoms were randomly displaced by as much as several atomic diameters. However, these variations were found to have no effect on the analysis presented in this paper and, here, we report only the results from the full, unaltered simulated structure. † Changing t over the range 0.5–1.0 nm has no major effect on the conclusions drawn.