Assessment of Local Observation of Atomic Ordering in Alloys via the Radial Distribution Function: A Computational and Experimental Approach

Journal Article · 23 December 2021 · Frontiers in Materials

DOI: https://doi.org/10.3389/fmats.2021.797418 · OSTI ID:1983089

Greenhalgh, Alexander D. ^[1]; Sanjeewa, Liurukara D. ^[2]; Luszczek, Piotr ^[1]; Maroulas, Vasileios ^[1]; Rios, Orlando ^[1]; Keffer, David J.  ^[1]

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1. University of Tennessee, Knoxville, TN (United States)
2. University of Missouri, Columbia, MO (United States)

As a powerful analytical technique, atom probe tomography (APT) has the capacity to acquire the spatial distribution of millions of atoms from a complex sample. However, extracting information at the Ångstrom-scale on atomic ordering remains a challenge due to the limits of the APT experiment and data analysis algorithms. The development of new computational tools enable visualization of the data and aid understanding of the physical phenomena such as disorder of complex crystalline structures. Here, we report progress towards this goal using two steps. We describe a computational approach to evaluate atomic ordering in the crystal structure by generating radial distribution functions (RDF). Atomic ordering is rendered as the Fractional Cumulative Radial Distribution Function (FCRDF) which allows for greater visibility of local compositions at short range in the structure. Further, we accommodate in the analysis additional parameters such as uncertainty in the atomic coordinates and the atomic abundance to ascertain short-range ordering in APT data sets. We applied the FCRDF analysis to synthetic and experimental APT data sets for Ni₃Al. The ability to observe a signal of atomic ordering consistent with the known L1₂ crystal structure is heavily dependent on spatial uncertainty, irrespective of abundance. Detection of atomic ordering is subject to an upper limit of spatial uncertainty of atoms described with Gaussian distributions with a standard deviation of 1.3 Å. The FCRDF analysis was also applied to the APT data set for a six-component alloy, Al_1.3CoCrCuFeNi. In this case, we are currently able to visualize elemental segregation at the nanoscale, though unambiguous identification of atomic ordering at the Ångstrom (nearest-neighbor) scale remains a goal.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States); University of Tennessee, Knoxville, TN (United States)
• Sponsoring Organization: USDOE Office of Energy Efficiency and Renewable Energy (EERE); USDOE Office of Science (SC)
• Grant/Contract Number: AC02-07CH11358
• OSTI ID: 1983089
• Journal Information: Frontiers in Materials, Journal Name: Frontiers in Materials Vol. 8; ISSN 2296-8016
• Publisher: Frontiers Research FoundationCopyright Statement
• Country of Publication: United States
• Language: English