arXiv subjects

Christopher A. Schuh

Publications and source records attributed to Christopher A. Schuh.

16 recordsLinked to original sources

arXiv2026

Irregular Metamaterial Networks

Metamaterials can achieve exceptional functionality through careful engineering of their mesoscale structure. Although appropriately introduced irregularities can be advantageous, current approaches largely conform to regular structures to preserve tractability. Here, we contend that network theory, enriched with geometry and physics, provides a natural framework for designing metamaterials with controlled irregularities at relevant scales, thereby enabling the discovery of new property-enhancing structures. We examine how this augmented network theory can facilitate the creation of irregular metamaterials with enhanced or novel properties and how metamaterial research, in turn, is opening new directions in network science. Supported by machine learning and advanced self-assembly, the emerging field of irregular metamaterial networks is poised to transform inverse design and scalable manufacturing of novel materials.

cond-mat.dis-nn↗

arXiv2025

The Augmented Potential Method: Multiscale Modeling Toward a Spectral Defect Genome

The modeling of solute chemistry at low-symmetry defects in materials is historically challenging, due to the computation cost required to evaluate thermodynamic properties from first principles. Here, we offer a hybrid multiscale approach called the augmented potential method that connects the chemical flexibility and near-quantum accuracy of a universal machine learning potential at the site of the defect, with the computational speed of a long-range classical potential implemented away from the defect site in a buffer zone. The method allows us to rapidly compute distributions of grain boundary segregation energy for 1,050 binary alloy pairs (including Ag, Al, Au, Cr, Cu, Fe, Mo, Nb, Ni, Pd, Pt, Ta and V, W solvent), creating a database for polycrystalline grain boundary segregation. This database is ~5x larger than previously published spectral compilations, and yet has improved accuracy. The approach can also address problems far beyond the reach of any other method, such as handling bcc Fe-based alloys, or the complex solute-solute interactions in random polycrystals. The approach thus paves a pathway toward a complete defect genome in crystalline materials.

cond-mat.mtrl-sci↗

arXiv2025

At extreme strain rates, pure metals thermally harden while alloys thermally soften

When materials are deformed at extreme strain rates, greater than $10^6 \text{ s}^{-1}$, a counterintuitive mechanical response is seen where the strength and hardness of pure metals increases with increasing temperature. The anti-thermal hardening is due to defects in the material becoming pinned by phonons in the crystal lattice. However, here, using optically driven microballistic impact testing to measure the dynamic strength and hardness, we show that when the composition is systematically varied away from high purity, the mechanical response of metals transitions from ballistic transport of dislocations back to thermally activated pinning of dislocations, even at the highest strain rates. This boundary from "hotter-is-stronger" to "hotter-is-softer" is observed and mapped for nickel, titanium, and gold. The ability to tune between deformation mechanisms with very different temperature dependencies speaks to new directions for alloy design in extreme conditions.

cond-mat.mtrl-sci↗

arXiv2025

Grain Boundary Segregation Spectra from a Generalized Machine-learning Potential

Modeling solute segregation to grain boundaries at near first-principles accuracy is a daunting task, particularly at finite concentrations and temperatures that require accurate assessments of solute-solute interactions and excess vibrational entropy of segregation that are computationally intensive. Here, we apply a generalized machine learning potential for 16 elements, including Ag, Al, Au, Cr, Cu, Mg, Mo, Ni, Pb, Pd, Pt, Ta, Ti, V, W and Zr, to provide a self-consistent spectral database for all of these energetic components in of 240 binary alloy polycrystals. The segregation spectra of Al-based alloys are validated against past quantum-accurate simulations and show improved predictive ability with some existing atom probe tomography experimental data.

cond-mat.mtrl-sci↗

arXiv2025

A Grain Boundary Embrittlement Genome for Substitutional Cubic Alloys

Grain boundary chemistry plays a critical role for the properties of metals and alloys, yet there is a lack of consistent datasets for alloy design and development. With the advent of artificial intelligence and machine learning in materials science, open materials models and datasets can be used to overcome such challenges. Here, we use a universal interatomic potential to compute a grain boundary segregation and embrittlement genome for the Σ5[001](210) grain boundary for FCC and BCC binary alloys. The grain boundary database calculated here serves as a design tool for the embrittlement of high-angle grain boundaries for alloys across 15 base metals system of Ag, Al, Au, Cr, Cu, Fe (both BCC and FCC), Mo, Nb, Ni, Pd, Pt, Rh, Ta, V and W with 75 solute elements for each.

cond-mat.mtrl-sci↗

arXiv2025

Grain Boundary Segregation and Embrittlement of Aluminum Binary Alloys from First Principles

Grain boundary segregation controls properties of polycrystalline materials such as their susceptibility to intergranular cracking. It is of interest to engineer alloy chemistry to enhance grain boundary cohesion to prevent intergranular failure. While there is collectively a large first-principles dataset for grain boundary embrittlement in multiple Al-based binary alloys, the methodologies used for the first principles calculations, as well as the analyzed fracture paths, are variable amongst studies. Here, we reevaluate and compute grain boundary segregation and embrittlement from all-electron first-principles for the Σ5[001](210) Al grain boundary. We explicitly evaluate multiple fracture paths, and provide a study case of the chemical trends of the preferred fracture paths across 69 binary Al alloys. The results suggest that neglecting certain low energy fracture paths can lead to errors of estimating embrittlement potency up to the order of 1 eV per solute atom, especially for multiple d-block transition metal solutes that are of engineering interest. The database calculated here also permits a comprehensive comparison between all-electron and pseudopotential methodologies. The effects of Hubbard U density functional theory on grain boundary segregation and embrittlement in Al(Sc) are found not to be significant in terms of the relative energetic calculations of grain boundaries and free surfaces (differences are of order 0.1 eV or less).

cond-mat.mtrl-sci↗

arXiv2024

Interstitial Solute Segregation at Triple Junctions: Implications for the Hydrogen Storage Properties of Nanomaterials

At very fine grain sizes, grain boundary segregation can deviate from conventional behavior due to triple junction effects. While this issue has been addressed in prior work for substitutional alloys, here we develop a framework that accounts for interstitial sites in the grains, grain boundaries, and triple junctions of model Pd(H) polycrystals. This approach allows computation of interstitial segregation spectra separately at both defect types, which permits an understanding of segregation at all grain sizes via a size-scaling spectral isotherm. The size dependencies of dilute Pd(H) are found to be influenced not only by the triple junction content, but also by grain size-dependent lattice strains; the latter effect is evidenced by size dependencies of individual grain boundary and junction subspectra. The framework proposed here is applicable to interstitial alloys in general, and may serve as a basis for interfacial engineering in interstitial nanocrystalline alloys. As an example, we show using the dilute limit isotherm that hydrogen density can triple in nanocrystalline vis-à-vis microcrystalline Pd due to hydrogen adsorption at intergranular defect sites.

cond-mat.mtrl-sci↗

arXiv2024

Designing for Cooperative Grain Boundary Segregation in Multicomponent Alloys

Tailoring the nanoscale distribution of chemical species at grain boundaries is a powerful method to dramatically influence the properties of polycrystalline materials. However, classical approaches to the problem have tacitly assumed that only competition is possible between solute species. In this paper, we show that solute elements can cooperate in the way they segregate to grain boundaries: in properly targeted alloys, the different chemical species cooperate to each fill complementary grain boundary sites disfavored by the other. By developing a theoretical "spectral" approach to this problem based on quantum-accurate grain boundary site distributions, we show how grain boundaries can be cooperatively alloyed, whether by depletion or enrichment. We provide machine-learned co-segregation information for over 700 ternary aluminum-based alloys, and experimentally validate the concept in one ternary alloy where co-segregation is not expected by prior models, but is expected based on the cooperative model.

cond-mat.mtrl-sci↗

arXiv2024

Grain Boundary Segregation Predicted by Quantum-Accurate Segregation Spectra but not by Classical Models

In alloys, solute segregation at grain boundaries is classically attributed to three driving forces: a high solution enthalpy, a high size mismatch, and a high difference in interfacial energy. These effects are generally cast into a single scalar segregation energy and used to predict grain boundary solute enrichment or depletion. This approach neglects the physics of segregation at many competing grain boundary sites, and can also miss electronic effects that are energetically significant to the problem. In this paper, we demonstrate that such driving forces cannot explain, nor thus predict, segregation in some alloys. Using quantum-accurate segregation spectra that have recently become available for some polycrystalline alloys, we predict strong segregation for gold in aluminum, a solvent-solute combination that does not conform to classical driving forces. Our experiments confirm these predictions and reveal gold enrichment at grain boundaries that is two orders of magnitude over the bulk lattice solute concentration.

cond-mat.mtrl-sci↗

arXiv2023

Can Symmetric Tilt Grain Boundaries Represent Polycrystals?

Grain boundaries control a wide variety of bulk properties in polycrystalline materials, so simulation methods like density functional theory are routinely used to study their structure-property relationships. A standard practice for such simulations is to use compact, high-symmetry (coincident site lattice) boundaries as representatives of the much more complex polycrystalline grain boundaries. In this letter, we question this practice by quantitatively comparing the spectra of atomic sites and properties amongst grain boundaries. We show, using solute segregation as an example property, that highly symmetric tilt boundaries (with Σ values less than 10) will fail to capture polycrystalline grain boundary environments, and thus lead to incorrect quantitative and qualitative insights into their behavior.

cond-mat.mtrl-sci↗

arXiv2023

The Spectrum of Interstitial Solute Energies in Polycrystals

A computational method is presented to measure the spectrum of segregation energies for an interstitial solute at grain boundaries (GBs) in a polycrystal. For the Pd-H system, that spectrum of GB interstitial segregation energies is found to consist of a mixture of two normal-like distributions, characteristic of GB octahedral and tetrahedral sites. We also derive a thermodynamic isotherm to calculate the equilibrium segregation state in a polycrystal that recognizes the need for referencing two interstitial site types, and show that it conforms well to experimental data in the Pd-H system.

cond-mat.mtrl-sci↗

arXiv2020

Crystal orientation and detector distance effects on resolving pseudosymmetry by electron backscatter diffraction

Accurately indexing pseudosymmetric materials has long proven challenging for electron backscatter diffraction. The recent emergence of intensity-based indexing approaches promises an enhanced ability to resolve pseudosymmetry compared to traditional Hough-based indexing approaches. However, little work has been done to understand the effects of sample position and orientation on the ability to resolve pseudosymmetry, especially for intensity-based indexing approaches. Thus, in this work we quantitatively investigate the effects of crystal orientation and detector distance in a model tetragonal ZrO2 (c/a=1.0185) material. We identify orientations that are easiest and most difficult to correctly index, characterize the effect of detector distance on indexing confidence, and analyze these trends based on the appearance of specific zone axes in the diffraction patterns. Our findings also point to the clear benefit of shorter detector distances for resolving pseudosymmetry using intensity-based indexing approaches.

cond-mat.mtrl-sci↗

arXiv2020

Resolving pseudosymmetry in tetragonal ZrO2 using EBSD with a modified dictionary indexing approach

Resolving pseudosymmetry has long presented a challenge for electron backscatter diffraction (EBSD) and has been notoriously challenging in the case of tetragonal ZrO2 in particular. In this work, a method is proposed to resolve pseudosymmetry by building upon the dictionary indexing method and augmenting it with the application of global optimization to fit accurate pattern centers, clustering of the Hough-indexed orientations to focus the dictionary in orientation space, and interpolation to improve the accuracy of the indexed solution. The proposed method is demonstrated to resolve pseudosymmetry with 100% accuracy in simulated patterns of tetragonal ZrO2, even with high degrees of binning and noise. The method is then used to index an experimental dataset, which confirms its ability to efficiently and accurately resolve pseudosymmetry in these materials. The present method can be applied to resolve pseudosymmetry in a wide range of materials, possibly even some more challenging than tetragonal ZrO2. Source code for this implementation is available online.

cond-mat.mtrl-sci↗

arXiv2019

Global optimization for accurate determination of EBSD pattern centers

Accurate pattern center determination has long been a challenge for the electron backscatter diffraction (EBSD) community and is becoming critically accuracy-limiting for more recent advanced EBSD techniques. Here, we study the parameter landscape over which a pattern center must be fitted in quantitative detail and reveal that it is both sloppy and noisy, which limits the accuracy to which pattern centers can be determined. To locate the global optimum in this challenging landscape, we propose a combination of two approaches: the use of a global search algorithm and averaging the results from multiple patterns. We demonstrate the ability to accurately determine pattern centers of simulated patterns, inclusive of effects of binning and noise on the error of the fitted pattern center. We also demonstrate the ability of this method to accurately detect changes in pattern center in an experimental dataset with noisy and highly binned patterns. Source code for our pattern center fitting algorithm is available online.

cond-mat.mtrl-sci↗

arXiv2016

Supersonic Impact of Metallic Micro-particles

Understanding material behavior under high velocity impact is the key to addressing a variety of fundamental questions in areas ranging from asteroid strikes and geological cratering to impact-induced phase transformations, spallation, wear, and ballistic penetration. Recently, adhesion has emerged in this spectrum since it has been found that micrometer-sized metallic particles can bond to metallic substrates under supersonic-impact conditions. However, the mechanistic aspects of impact-induced adhesion are still unresolved. Here we study supersonic impact of individual metallic microparticles on substrates with micro-scale and nanosecond-level resolution. This permits the first direct observation of a material-dependent threshold velocity, above which the particle undergoes impact-induced material ejection and adheres to the substrate. Our finite element simulations reveal that prevailing theories of impact-induced shear localization and melting cannot account for the material ejection. Rather, it originates from the propagation of a pressure wave induced upon impact. The experiments and simulations together establish that the critical adhesion velocity for supersonic microparticles is proportional to the bulk speed of sound.

cond-mat.mtrl-sci↗

arXiv2015

Segregation-induced changes in grain boundary cohesion and embrittlement in binary alloys

Grain boundary embrittlement occurs when a solute enriches at a grain boundary and lowers its cohesive energy. While grain boundary enrichment is often attributed to equilibrium segregation effects, most models of embrittlement consider either the energetics of decohesion or the equilibrium adsorption at the boundary, but not both phenomena together. We develop a model for the change in cohesive energy of a grain boundary of a pure metal upon introduction of solute under conditions of equilibrium segregation prior to fracture. A heuristic grain boundary cohesion map is presented to delineate whether a given solute-solvent pair will exhibit weakening or strengthening of grain boundaries. The analysis helps to clarify that grain boundary embrittlement requires a solute that will both lower the cohesive energy of the boundary and segregate to it in the first place. The map reasonably captures known metal-metal embrittling pairs.

cond-mat.mtrl-sci↗