arXiv subjects

Emmanuelle A. Marquis

Publications and source records attributed to Emmanuelle A. Marquis.

6 recordsLinked to original sources

arXiv2026

Role of diffusion-induced grain boundary migration during molten salt corrosion of a Ni-30Cr alloy

The response of Ni-Cr alloys to exposure to molten chloride and fluoride salts is typically characterized by Cr dealloying with the formation of a Cr-depleted bi-continuous porous subsurface layer. The exact mechanism behind the loss of Cr over distances unattainable by lattice diffusion alone is still debated. To address this question, two different surface finishes, namely electropolished and sanded, of a Ni-30Cr alloy were exposed to LiCl-KCl-2wt% EuCl3 eutectic salt at 500 °C for 96 hours. In the absence of fast diffusion pathways, dissolution occurred layer by layer and was kinetically controlled by Ni dissolution, as observed over the grain interiors of the electropolished sample. Grain boundaries were subject to diffusion-induced grain boundary migration (DIGM), leading to the formation of pure Ni islands above grain boundaries. This overall behavior contrasted with the sanded surface response that was characterized by several micrometer deep interconnected porosity and complete Cr depletion. DIGM of the dense grain boundaries created by recrystallization of the sanded surface was responsible for the observed sub-surface microstructure. This work unequivocally establishes DIGM as a key mechanism in alloy molten salt corrosion, and microstructure as a decisive contributor to an alloy's corrosion response.

cond-mat.mtrl-sci↗

arXiv2026

Frontiers of atom probe tomography physics, data processing, and analysis

Atom probe tomography (APT) fills a crucial need in the characterization workflow of materials by its ability to inform the 3D chemical microstructure at the nanoscale. As with any characterization techniques, APT has strengths and limitations that inform the interpretation of the data. Therefore, a challenge for the materials characterization community, and the APT community in particular, is the need to establish repeatable and reproducible workflows around the APT data acquisition, reconstruction, analysis, and sharing, in order to inform interpretation. Data interpretation also requires the continued development of our understanding of the physical processes responsible for field evaporation. We review recent developments in the experimental analysis of field evaporation and in the modeling of field evaporation leading to new understanding of common artifacts observed in reconstructed data. We then discuss current challenges with data analysis, translation of results, and data interpretation in the absence of community-agreed standards, and therefore, the crucial need for standardization at every stage of APT research, from data collection all the way to data reporting. This perspective is a summary of the invited presentations and discussions that took place during a workshop (August 4-5, 2024, Alexandria, Virginia, USA).

cond-mat.mtrl-sci↗

arXiv2022

Ab-Initio Simulation of Field Evaporation

A new simulation approach of field evaporation is presented. The model combines classical electrostatics with molecular dynamics (MD) simulations. Unlike previous atomic-level simulation approaches, our method does not rely on an evaporation criterion based on thermal activation theory, instead, electric-field-induced forces on atoms are explicitly calculated and added to the interatomic forces. Atoms then simply move according to the laws of classical molecular dynamics and are "evaporated" when the external force overcomes interatomic bonding. This approach thus makes no ad-hoc assumptions concerning evaporation fields and criteria, which makes the simulation fully physics-based and "ab-initio" apart from the interatomic potential. As proof of principle, we perform simulations to determine material dependent critical voltages which allow assessing the evaporation fields and the corresponding steady-state tip shapes in different metals. We also extract critical evaporation fields in elemental metals and sublimation energies in a high entropy alloy to have a more direct comparison with tabulated values. In contrast to previous approaches, we show that our method is able to successfully reproduce the enhanced zone lines observed in experimental field desorption patterns. We also demonstrate the need for careful selection of the interatomic potential by a comparative study for the example of Cu-Ni alloys.

cond-mat.mtrl-sci↗

arXiv2022

Origin of Enhanced Zone Lines in Field Desorption Maps

Artifacts in the collective desorption map of the detector hits impede a truthful reconstruction, including enhanced "zone lines" with high atomic impact intensity. Since APT is destructive, simulation is the only approach to explain the origin of these zone lines, but previous work couldn't reproduce them. Here, we use a new simulation technique that adds the full electrostatic forces to the interatomic forces in a molecular-dynamics simulation and eliminates the previous ad-hoc assumptions. We find for the canonical example of tungsten that evaporation happens when the electrostatic force overpowers the interatomic force, and the misalignment of the two forces deviates the launch direction of the atoms in certain zones, giving rise to an accumulation of hit events around zone lines.

cond-mat.mtrl-sci↗

arXiv2019

Flux effects in precipitation under irradiation - Simulation of Fe-Cr alloys

Radiation-enhanced precipitation of Cr-rich α' in irradiated Fe-Cr alloys, which results in hardening and embrittlement, depends on the irradiating particle and the displacement per atom (dpa) rate. Here, we utilize a Cahn-Hilliard phase-field based approach, that includes simple models for nucleation, irradiating particle and rate dependent radiation-enhanced diffusion and cascade mixing to simulate α' evolution under neutrons, heavy ions, and electron irradiations. Different irradiating particles manifest very different cascade mixing efficiencies. The model was calibrated using neutron data. For cascade inducing neutron/heavy-ion dpa rates at 300 °C between 10^-^8 and 10^-^6 dpa/s the model predicts approximately constant number density, decreasing radius, decreasing α' Cr composition, and lower α' volume fraction. The model then predicts a dramatic transition to no α' formation above approximately 10^-^5 dpa/s, while electron irradiation, with weak mixing, had little effect at dpa rates up to 10^-^3 dpa/s. These model predictions are consistent with experiments. We explain the results in terms of the flux dependence of the radiation enhanced diffusion, cascade mixing, and their ratio, which all vary significantly in relevant flux ranges for neutron and cascade inducing ion irradiations. These results show that both cascade mixing and radiation enhanced diffusion must be accounted for when attempting to emulate neutron-irradiation effects using accelerated ion irradiations.

cond-mat.mtrl-sci↗

arXiv2015

Effects of the local structure dependence of evaporation fields on field evaporation behavior

Accurate three dimensional reconstructions of atomic positions, and full quantification of the information contained in atom probe tomography data relies on understanding the physical processes taking place during field evaporation of atoms from needle-shaped specimens. However, the modeling framework for atom probe tomography has remained qualitative at best. Building on the continuum field models previously developed, we introduce a more physical approach with the selection of evaporation events based on density functional theory calculations. This new model reproduces key features observed experimentally in terms of sequence of evaporation, desorption maps, and depth resolution, and provides insights into the physical limit for spatial resolution.

physics.atom-ph↗