Energy-filtered imaging of interfacial composition in complex Ni-base superalloys
In a wide variety of important engineering materials, including structural Ni, Fe, and Al-base alloys, the study of compositional gradients that occur at grain boundaries and other interfaces due to the precipitation of solute-rich second phases is of critical importance. X-ray spectrometry in the analytical electron microscope (AEM) has been used for many years to study solute depletion at interfaces in these alloys. It has been particularly effective at providing accurate, quantitative measurements in cases where the interface precipitates are spaced far apart and where relatively wide compositional gradients result from diffusion-controlled “collector-plate” mechanisms. However, in complex alloys, with heavy grain boundary coverage, multiple precipitate types, and/or multiphase matrices, x-ray microanalysis is more limited due to beam spreading and die associated 5-20nm spatial resolution achieved in these alloys with AEMs equipped with thermionic sources.Elemental mapping in an AEM equipped with an imaging energy-filter is an alternative method for the study of interface compositional gradients. It has been shown to be effective for this purpose in relatively simple situations in steels.