Quantification of Solute Topology in Atom Probe Tomography Data: Application to the Microstructure of a Proton-Irradiate
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Quantification of Solute Topology in Atom Probe Tomography Data: Application to the Microstructure of a Proton-Irradiated Alloy 625 IMAN GHAMARIAN, LI-JEN YU, and EMMANUELLE A. MARQUIS The analysis of solute clustering in atom probe tomography (APT) has almost exclusively relied on a simple algorithm based on the simple friend-of-friend analysis where a threshold distance or maximum separation defines whether atoms are part of a cluster or part of the matrix. This method is however limited to very specific microstructures and is very sensitive to parameter selection. To expand the range and applicability of current APT analysis tools, we introduce new quantitative data analysis methods based on density-based hierarchical clustering algorithms and relevant to solute clustering and segregation. We demonstrate the methods’ performance on the complex microstructure developing in a proton-irradiated Alloy 625, specifically focusing on the analyses of nanoscale Al clusters, Si clusters, and Si-decorated dislocation loops. https://doi.org/10.1007/s11661-019-05520-6 The Minerals, Metals & Materials Society and ASM International 2019
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INTRODUCTION
MATERIALS characterization finds its purpose in the understanding and quantification of the relationships between processing parameters, microstructure, and properties. Standardized quantitative methods and algorithms have been developed for many characterization techniques, such as extracting grain size information from metallography data, or precipitate size and shape from electron microscopy imaging. The technique of atom probe tomography (APT), on the other hand, is still waiting for standardized, reproducible, and quantitative methods to be developed and adopted by the APT community. APT generates three-dimensional reconstructions containing information on the position and identity of a fraction of the atoms (typically between 50 and 80 pct) contained in the sampled volume of material. For a detailed background on the technique, please refer to published monographs.[1,2] In brief, the volume of interest is prepared in the form of a sharp needle with typical dimensions of 50 to 150 nm apex radius. The needle is placed at cryogenic temperature (< 50 K) and subjected to a high electric field (few to
IMAN GHAMARIAN, LI-JEN YU, and EMMANUELLE A. MARQUIS are with Department of Materials Science and Engineering, University of Michigan, Ann Arbor, MI, 48104. Contact e-mail: [email protected]. Manuscript submitted May 21, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS A
tens of V/nm). Thermal or voltage pulses are then used to trigger field evaporation of surface atoms. The atomic identity of the evaporating ions is inferred from timeof-flight measurements. The ions¢ original locations on the specimen surface are estimated using idealized specimen geometry and ion trajectories. Depth information is calculated from the evaporation sequence. A reconstructed volume is therefore constituted of discrete points where atoms are inferred to be located. In reality, spatial positioning accuracy
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