arXiv subjects

Daniel L. Foley

Publications and source records attributed to Daniel L. Foley.

3 recordsLinked to original sources

arXiv2025

Designing Corrosion-Resistant CoCrNi Medium Entropy Alloys via Short-Range Order Modification

Equiatomic CoCrNi medium entropy alloys are known for their unique properties linked to chemical short-range order (CSRO), crucial in both percolation processes and/or nucleation and growth processes influencing alloy passivation in aqueous environments. This study combines extended x-ray absorption fine structure, atomistic simulations, electrochemical methods, x-ray photoelectron spectroscopy, and transmission electron microscopy to explore CSRO evolution, passive film formation, as well as its characteristics in the as-homogenized CoCrNi condition, both before and after aging treatment. Results reveal a shift in local alloying element bonding environments post-aging, with simulations indicating increased Cr-Cr CSRO in 2nd nearest neighbor shells. Enhanced passive film formation kinetics and superior protection of the aged alloy in harsh acidified 3 mol/L NaCl solution indicate improved aqueous passivation correlated with Cr-Cr CSRO. This work establishes a direct connection between alloy CSRO and aqueous passivation in CoCrNi, highlighting its potential for tailored corrosion-resistant applications.

cond-mat.mtrl-sci↗

arXiv2023

An experimental high-throughput to high-fidelity study towards discovering Al-Cr containing corrosion-resistant compositionally complex alloys

Compositionally complex alloys hold the promise of simultaneously attaining superior combinations of properties, such as corrosion resistance, light-weighting, and strength. Achieving this goal is a challenge due in part to a large number of possible compositions and structures in the vast alloy design space. High-throughput methods offer a path forward, but a strong connection between the synthesis of an alloy of a given composition and structure with its properties has not been fully realized to date. Here, we present the rapid identification of corrosion-resistant alloys based on combinations of Al and Cr in a base Al-Co-Cr-Fe-Ni alloy. Previously unstudied alloy stoichiometries were identified using a combination of high-throughput experimental screening coupled with key metallurgical and electrochemical corrosion tests, identifying alloys with excellent passivation behavior. The alloy native oxide performance and its self-healing attributes were probed using rapid tests in deaerated 0.1 mol/L H2SO4. Importantly, a correlation was found between the electrochemical impedance modulus of the exposure-modified air-formed film and self-healing rate of the CCAs. Multi-element extended x-ray absorption fine structure analyses connected more ordered type chemical short-range order in the Ni-Al 1st nearest-neighbor shell to poorer corrosion resistance. This report underscores the utility of high throughput exploration of compositionally complex alloys for the identification and rapid screening of a vast stoichiometric space.

cond-mat.mtrl-sci↗

arXiv2021

Mapping Structural Heterogeneity at the Nanoscale with Scanning Nano-structure Electron Microscopy (SNEM)

Here we explore the use of scanning electron diffraction coupled with electron atomic pair distribution function analysis (ePDF) to understand the local order as a function of position in a complex multicomponent system, a hot rolled, Ni-encapsulated, Zr$_{65}$Cu$_{17.5}$Ni$_{10}$Al$_{7.5}$ bulk metallic glass (BMG), with a spatial resolution of 3 nm. We show that it is possible to gain insight into the chemistry and chemical clustering/ordering tendency in different regions of the sample, including in the vicinity of nano-scale crystallites that are identified from virtual dark field images and in heavily deformed regions at the edge of the BMG. In addition to simpler analysis, unsupervised machine learning was used to extract partial PDFs from the material, modeled as a quasi-binary alloy, and map them in space. These maps allowed key insights not only into the local average composition, as validated by EELS, but also a unique insight into chemical short-range ordering tendencies in different regions of the sample during formation. The experiments are straightforward and rapid and, unlike spectroscopic measurements, don't require energy filters on the instrument. We spatially map different quantities of interest (QoI's), defined as scalars that can be computed directly from positions and widths of ePDF peaks or parameters refined from fits to the patterns. We developed a flexible and rapid data reduction and analysis software framework that allows experimenters to rapidly explore images of the sample on the basis of different QoI's. The power and flexibility of this approach are explored and described in detail. Because of the fact that we are getting spatially resolved images of the nanoscale structure obtained from ePDFs we call this approach scanning nano-structure electron microscopy (SNEM), and we believe that it will be powerful and useful extension of current 4D-STEM methods.

cond-mat.mtrl-sci↗