A multicomponent Fe-Cu based steel is studied using atom-probe tomography. The precipitates are identified using two different methodologies and subsequent morphological and compositional results are compared. The precipitates are first identified using a maximum separation distance algorithm, the envelope method, and then by a concentration threshold method, an isoconcentration surface. We discuss in detail the proper selection of the parameters needed to delineate precipitates utilizing both methods. The results of the two methods exhibit a difference of 44 identified precipitates, which can be attributed to differences in the basis of both methods and the sensitivity of our results to user-prescribed parameters. The morphology of the precipitates, characterized by four different precipitate radii and precipitate size distribution functions (PSDs), are compared and evaluated. A variation of less than ∼8% is found between the different radii. Two types of concentration profiles are compared, giving qualitatively similar results. Both profiles show Cu-rich precipitates containing Fe with elevated concentrations of Ni, Al, and Mn near the heterophase interfaces. There are, however, quantitative disagreements due to differences in the basic foundations of the two analysis methods.

The influence of W on the temporal evolution of γ′ precipitation toward equilibrium in a model Ni-Al-Cr alloy is investigated by three-dimensional atom-probe (3DAP) microscopy and transmission electron microscopy (TEM). We report on the alloys Ni-10 Al-8.5 Cr (at.%) and Ni-10 Al-8.5 Cr-2 W (at.%), which were aged isothermally in the γ + γ′ two-phase field at 1073 K, for times ranging from 0.25 to 264 h. Spheroidal-shaped γ′ precipitates, 5–15 nm diameter, form during quenching from above the solvus temperature in both alloys at a high number density (∼1023 m−3). As γ′ precipitates grow with aging at 1073 K, a transition from spheriodal- to cuboidal-shaped precipitates is observed in both alloys. The elemental partitioning and spatially resolved concentration profiles across the γ′ precipitates are obtained as a function of aging time from three-dimensional atom-by-atom reconstructions. Proximity histogram concentration profiles (Hellman et al., 2000) of the quaternary alloy demonstrate that W concentration gradients exist in γ′ precipitates in the as-quenched and 0.25-h aging states, which disappear after 1 h of aging. The diffusion coefficient of W in γ′ is estimated to be 6.2 × 10−20 m2 s−1 at 1073 K. The W addition decreases the coarsening rate constant, and leads to stronger partitioning of Al to γ′ and Cr to γ.

The results of a three-dimensional atom probe (3DAP) analysis, on a subnanometer scale, of a ceramic/metal heterophase interface, MgO/Cu, are presented. Segregation of Ag, from the Cu (Ag) matrix, at MgO/Cu interfaces is investigated and the Gibbsian interfacial excess of silver is determined; the range is 2.33 × 1018 to 5.81 × 1018 m−2. Also, silver segregation at the same MgO/Cu interfaces is analyzed employing a new approach that utilizes a proximity histogram or proxigram.

The three-dimensional (3D) atom-probe technique produces a reconstruction of the elemental chemical identities and three-dimensional positions of atoms field evaporated from a sharply pointed metal specimen, with a local radius of curvature of less than 50 nm. The number of atoms collected can be on the order of one million, representing an analysis volume of approximately 20 nm × 20 nm × 200 nm (80,000 nm3). This large amount of data allows for the identification of microstructural features in a sample, such as grain or heterophase boundaries, if the feature density is large enough. Correlation of the measured atomic positions with these identified features results in an atom-by-atom description of the chemical environment of crystallographic defects. This article outlines a data compilation technique for the generation of composition profiles in the vicinity of interfaces in a geometrically independent way. This approach is applied to quantitative determination of interfacial segregation of silver at a MgO/Cu(Ag) heterophase interface.