The Influence of Isoconcentration Surface Selection in Quantitative Outputs from Proximity Histograms

Abstract

Isoconcentration surfaces are commonly used to delineate phases in atom probe datasets. These surfaces then provide the spatial and compositional reference for proximity histograms, the number density of particles, and the volume fraction of particles within a multiphase system. This paper discusses the influence of the isoconcentration surface selection value on these quantitative outputs, using a simple oxide dispersive strengthened alloy, Fe91Ni8Zr1, as the case system. Zirconium reacted with intrinsic oxygen impurities in a consolidated ball-milled powder to precipitate nanoscale zirconia particles. The zirconia particles were identified by varying the Zr-isoconcentration values as well as by the maximum separation data mining method. The associated outputs mentioned above are elaborated upon in reference to the variation in this Zr isosurface value. Considering the dataset as a whole, a 10.5 at.% Zr isosurface provided a compositional inflection point for Zr between the particles and matrix on the proximity histogram; however, this value was unable to delineate all of the secondary oxide particles identified using the maximum separation method. Consequently, variations in the number density and volume fraction were observed as the Zr isovalue was changed to capture these particles resulting in a loss of the compositional accuracy. This highlighted the need for particle-by-particle analysis.

On Strong-Scaling and Open-Source Tools for High-Throughput Quantification of Material Point Cloud Data: Composition Gradients, Microstructural Object Reconstruction, and Spatial Correlations

“…The carbide example documents a sensitivity of the shape and composition to ϕ C . These findings confirm that a single threshold value is in most cases inadequate to distinguish objects via iso-contour approximation techniques [54][55][56][57]. Our work solves how these inherent limitations of iso-surfaces can at least be studied quantitatively in an exactly reproducible and fully automated manner.…”

“…This revealed unsolved challenges: Some are conceptual, like the assumption that using a single threshold value suffices to segment a dataset into useful isosurfaces. As this work supports this is an often inadequate [55][56][57]. Other challenges, like data accessibility restrictions in commercial software, pose practical barriers with respect to how completely computational geometry, concentration field, and detailed metadata are exportable [21,58]; and thus how APM research studies are (programmatically) comparable to one another and can become FAIR-compliant.…”

“…However, as Larson et al pointed out [4], applying delocalization always calls for making a compromise between how strongly one smears positions in an effort to achieve blunter surfaces and smoother composition gradients but to smear not too strongly to render very different or even questionable numerical results. Several authors reported in fact a strong parameter sensitivity of iso-surfaces [54][55][56], and suggested improvements but these remained, with few exceptions [61], at the level of accepting the results from commercial tools oftentimes paired with very tedious manual inspection. To close this gap was our incentive to implement an open-source alternative.…”

Solving Peak Overlaps for Proximity Histogram Analysis of Complex Interfaces for Atom Probe Tomography Data

“…While it is possible to separate the ions and get a more detailed analysis than would be possible with a 1D concentration profile, it becomes clear that the generation of isosurfaces itself has a great influence on the results obtained. This is a known problem and has already been discussed in the past (Hornbuckle et al, 2015;Martin et al, 2016;Barton et al, 2019).…”

Compensating Local Magnifications in Atom Probe Tomography for Accurate Analysis of Nano-Sized Precipitates

“…Since extracting the size and shape of nano-precipitates directly from an APT reconstruction (e.g., by evaluation of the volume within an isosurface) depends strongly on the coarse-graining process and the user-defined interface between the precipitate and the matrix (Barton et al, 2019), the size of precipitates is easily over-or underestimated if too many or too few atoms are considered as belonging to the precipitate. An alternative method is to calculate the radius of gyration r g from the coordinates of the constituent atoms i by…”