Interfacial excess of solutes across phase boundaries using atom probe microscopy

Three-dimensional elemental mapping in atom probe microscopy provides invaluable insights into the structure and composition of interfaces in materials. Quasi-atomic resolution facilitates access to the solute decoration of grain boundaries, advancing the knowledge on local segregation and depletion phenomena. More recent developments unlocked three-dimensional mapping of the interfacial excess across grain boundaries. Such detailed understanding of the local structure and composition of these interfaces enabled advancements in processing methods and material development. However, many engineering alloys, such as Ni-based superalloys, have much more complex microstructures with various solutes and precipitates in close proximity to grain boundaries. The complex interaction of grain boundary segregation and grain boundary precipitates requires precise compositional control. However, abrupt changes in solute solubility across phase boundaries obscure the interfacial excess in proximity to grain boundaries. Therefore, this study provides a methodological framework of the quantitative characterization of phase boundaries in proximity to grain boundaries using atom probe microscopy. The detailed mass spectrum ranging of MC, M23C6, and M6C carbides is explored in order to achieve satisfactory compositional information. Proximity histograms and correlating concentration difference profiles determine the interface location, where a Gibbs dividing surface is not accessible. This enables reliable direct calculation of the interfacial excess across phase boundaries. Intuitively interpretable and quantitative 'interface plots' are introduced, and showcased for phase boundaries between gamma-matrix, gamma' precipitates, GB-gamma', MC, M23C6, and M6C carbides. The presented framework advances access to the local composition in proximity to grain boundaries and may be applicable to other engineering alloys or materials with functional properties.