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Item type:Publication, Access status: with files , Scalable fabrication and mechanical behaviour of hierarchical porous nickel networksAs the demand for light-weight structural and functional materials grows, the fabrication of hierarchical, high-performance micro- and nano-architectures becomes increasingly important. Here, we present a scalable alloying–dealloying strategy to fabricate porous metal with two- and three-level hierarchical networks (2 L-/3L-HN). By exploiting the vapour pressure difference between Ni and Zn, vapour phase alloying of Ni foam with Zn, followed by vapour phase dealloying of the resulting γ-Zn84Ni16 foam, generates a second hierarchical level, producing 2L-HN Ni or 2L-HN β-Zn50Ni50. Re-alloying 2L-HN β-Zn50Ni50 to 2L-HN γ-Zn84Ni16 via vapour phase alloying while preserving its hierarchical architecture enables chemical dealloying to create a third level of hierarchy at the nanoscale, producing 3L-HN Ni with significantly increased specific surface area. A novel scaling law is proposed to predict the mechanical properties of these hierarchical porous metallic networks as a function of solid fraction, and its validity is supported by compression tests on 2L-HN Ni with varying densities. This work establishes a scalable and versatile route for fabricating multiscale porous metallic networks with light-weight, tunable mechanical performance and high surface area.Publicationtype: Journal Article21 10 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Micromechanical insights into tensile deformation of epoxy-infiltrated hierarchical nanoporous copperHierarchical nanoporous metals infiltrated with polymers offer enhanced tensile stability while retaining functional porosity, yet their micromechanical deformation mechanisms remain insufficiently understood. Here, a micromechanics-based finite element framework is developed for epoxy-filled hierarchical nanoporous copper (HNPCu) based on experimentally derived structural parameters. The hierarchical ligament architecture across two structural levels as well as selective epoxy infiltration are explicitly resolved, enabling phase-specific analysis of local stress and strain evolution. The predicted tensile response is validated against experiments for different Cu solid fractions (0.1≤φ≤0.2), and the experimentally observed trends are well reproduced using idealized microstructures. Epoxy infiltration markedly reduces plastic strain localization within the Cu network, leading to a more homogeneous deformation state compared to epoxy-free HNPCu. At the macroscopic level, the tensile response remains largely unaffected by epoxy infiltration at small strains, with differences emerging only at larger deformation. Strain localization is predicted both within Cu ligaments and near Cu–epoxy interfaces, consistent with experimentally observed microcrack formation along phase boundaries and inside the Cu network. These findings provide micromechanical insight into hierarchy-assisted deformation in polymer-infiltrated nanoporous metals and establish a basis for microstructure-guided design of mechanically robust hierarchical materials.Publicationtype: Journal Article25 19 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , The Cahn–Hilliard residuum and its implications for critical-point wetting at solid solution surfacesAs part of their seminal 1958 analysis of nonuniform solutions, Cahn and Hilliard [J. Chem. Phys. 28, 258–267 (1958)] identified the Laplacian of the composition field as the key contribution to the excess free energy in solids with a conserved network of discrete atomic sites. Integration by parts converted to the now familiar gradient-square form underlying phase-field simulations and studies of critical-point wetting. The residuum from the integration by parts has since been ignored. Here, we examine its implications using critical-point wetting at the surface of an Ising-type solid solution for a representative case. As a benchmark, atomistic Monte Carlo simulation shows a continuous increase in wetting-layer thickness up to the bulk critical temperature. In contrast, the classical gradient-square continuum model predicts a first-order wetting transition. A more realistic Laplacian-based continuum formulation does not readily admit physically meaningful minimization by standard variational methods. As a discrete approach, a plane-by-plane model with an excess energy based on a second-difference (curvature) operator yields solutions consistent with the benchmark. Summation by parts transforms this operator into a first-difference- (gradient-) square form, and neglect of the residual term again leads to an incorrect first-order transition. Thus, the choice between curvature and gradient-square formulations alters the predicted character—first-order transition or continuous evolution in layer thickness—of the wetting, underscoring the fundamental importance of this choice.Publicationtype: Journal Article23 27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Impedance-based estimation of process parameters in electrolytic systems via circuit-embedded neural network (CENN)(American Chemical Society (ACS), 2026-07-09); ; ; ; We present a physics-aware machine learning framework for real-time estimation of electrolyte concentration and temperature from electrochemical impedance spectroscopy (EIS) measurements. Using nanoporous gold electrodes in aqueous H₂SO₄ as a model system, impedance spectra were acquired across concentrations of 1−20 mM and temperatures of 26−50 °C. The spectra were interpreted using a ZARC + transmission-line equivalent circuit and globally fitted over the full (c, T) domain, revealing two characteristic time scales associated with interfacial charge transfer and porous transport. The resulting physically consistent parameter maps were embedded into a circuit-informed neural network, enabling high-fidelity forward prediction of full impedance spectra directly from state variables (RMSE = 0.06 Ω). Inversion of this model allowed accurate estimation of electrolyte properties from measured spectra, achieving mean absolute errors of 0.10 mM in concentration and 1.0 °C in temperature. To further ccelerate sensing, Jacobian-based sensitivity analysis identified three informative frequencies that preserved essential spectral information. This reduced acquisition time by more than 95%-from minutes to under 6 s-while maintaining high accuracy (0.12mM, 1.1 °C). Although demonstrated for a specific electrochemical system, the proposed framework provides an interpretable and transferable workflow for rapid multiparameter sensing, provided that the equivalent-circuit structure and calibration domain are adapted to the target system.Publicationtype: Journal Article37 64 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Physics‐informed recurrent neural networks for predicting elasto‐plastic behavior in hierarchical finite element modelingNanoporous gold, with its hierarchical structure comprising interconnected networks on multiple length scales, poses significant computational challenges for traditional modeling methods. To solve this challenge, this study introduces a physics‐informed recurrent neural network (RNN) to model the homogenized material response of a diamond beam‐based representative volume element representing the lower level of hierarchy (LL), which was integrated as a material subroutine within an upper level (UL) finite element simulation. The RNN predicts the tangent stiffness matrix as a primary output from given strain trajectories. Secondary outputs such as stress, plastic strain, and plastic energy increments are derived through embedded physical relationships, ensuring physical consistency across the outputs. The RNN architecture enforces positive energy dissipation inherently through positive eigenvalues of the tangent stiffness matrix and further through penalization of negative energy increments, promoting thermodynamically consistent predictions. A two‐level hierarchical approach is employed, where the 2D UL model is subjected to uniaxial strain, while multiaxial strain conditions naturally arise locally within the structure. The inclusion of the LL significantly modifies the strain trajectories observed at the UL, while stress trajectories, although maintaining their general trend, experience considerable changes in magnitude. This approach demonstrates the capability to efficiently simulate hierarchical materials, capturing the influence of LL porosity on the UL material behavior while maintaining physical consistency. Additionally, the model allows for straightforward integration into finite element frameworks like Abaqus, offering a computationally efficient method for studying complex hierarchical materials.Publicationtype: Journal Article7 2 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Microstructure refinement and bicontinuity formation by distributed internal melting at the Ni₃Sn₄ peritecticGuided by a current interest in processing schemes, such as liquid-metal dealloying, providing fine-scale bicontinuous metal microstructures, we investigate the microstructure evolution during the peritectic melting of Ni₃Sn₄. The product microstructure is an interconnected array of spherical clusters of crystallographically aligned Ni₃Sn₂ ligaments, interpenetrated by a contiguous liquid phase. When quenched to room temperature, the prevalent microstructure consists of two interpenetrating solid phases. Leaching the solidified Sn melt produces monolithic porous bodies of Ni₃Sn₂. The characteristic structure size can reach down to 2 μm, a microstructure refinement by almost 2 orders of magnitude as compared to the 150 μm grain size of the master alloy. Remarkably, a more severe refinement is achieved at higher annealing temperatures. Our experiments identify liquid-film migration as the controlling process, here concurrent with constitutional supercooling and cellular solidification. We argue that peritectic melting exemplifies a more general family of processes of distributed internal melting (DIM). These processes exploit the abundant nucleation of regions of melt, finely distributed throughout a parent microstructure, when the alloy is heated into a two-phase solid–liquid regime of its phase diagram. DIM provides a novel and versatile pathway to fine-scale bicontinuous microstructures.Publicationtype: Journal Article63 60 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Rate equation for the transfer of interstitials across interfaces between equilibrated crystalsThis Letter inspects the thermally activated transfer of solute particles across the interface between two interstitial solid solution phases that equilibrate internally by fast diffusion on conserved arrays of sites. When each phase is considered as an ergodic ensemble of particles, statistical mechanics predicts the occupancy of the transition states at equilibrium to depend on the barrier energy and on the chemical potentials and vacancy fractions in each of the phases. A rate law for the nonequilibrium interfacial transfer, based on a constant transition probability between activated states, naturally satisfies the principle of detailed balance. Contrary to Butler-Volmer-type laws, values of the particle chemical potentials enter explicitly rather than through their differences. This, along with the dependency on the vacancy fractions, implies here an exchange flux density that depends explicitly on the compositions at equilibrium. The results can explain experimental observations of a drastic slowdown in the charging of metal hydrides near phase transformations or miscibility-gap critical points.Publicationtype: Journal Article53 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Strengthening mechanism in Al–Cu–Li alloy processed by friction consolidation followed by high-pressure torsion(Elsevier, 2026-01-15); ; ; ; The primary objective of this study is to explore the precipitation behavior of Al–Cu–Li alloy powder processed through a two-step approach: friction consolidation (FC) followed by high-pressure torsion (HPT). Microstructure analysis by scanning electron microscope shows a refined microstructure after FC, with a further reduction in grain size following HPT. X-ray diffraction analysis confirmed the formation of T1, T2, and 𝛿 precipitates after FC, which persisted even after HPT. Small-angle X-ray scattering shows a reduction in the volume fraction of larger precipitate particles after HPT, while the smaller grain volume fraction increased. Additionally, the volume fraction of precipitates decreased as a function of strain. To understand the contributions of various mechanisms to an enhanced hardness observed after HPT, a physical model was employed. This study explores how HPT influences dislocation behavior, precipitation, and grain size, highlighting its role in tailoring the microstructure and properties of the friction consolidated Al–Cu–Li alloy.Publicationtype: Journal Article55 12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Non-proportional plastic deformation at the micron scale: Single crystal Cu cantilever beams subjected to orthogonal bending(Elsevier, 2026-01); ; ; ; Experiments involving abrupt non-collinear changes in the direction of loading in the plastic range have been performed on micron-scale, single crystal Cu cantilever beams to provide the first data of its kind on non-proportional loading. The data is used to assess whether existing strain gradient plasticity (SGP) theories are capable of reproducing complex deformation histories representative of micron-scale metal forming processes, for which non-proportional loading is common. The data is also used to explore an issue that has arisen in efforts to develop SGP that is sufficiently accurate for engineering applications and yet not overly complex. Specifically, using a combination of experimentation and computation, the paper examines the differences in predictions made by two classes of theories presently in the mainstream, termed “incremental” and “non-incremental”, when non-proportional plastic loading occurs at the micron scale. Orthogonal bend experiments are performed on Cu single crystal cantilever beams with square cross-sections that are symmetrically oriented with respect to the vertical and horizonal bending axes. In Stage 1, the force applied to the end of the cantilever is vertical, producing bending in the vertical plane. Abruptly, in Stage 2, a horizontal force is applied with either the vertical force held constant (force control) or the vertical end-displacement of the beam held constant (displacement control). Three cantilever sizes, with widths of the square cross-section of 2, 5 and 20 microns, have been tested. The strength elevation for cantilever widths decreasing from 20 to 2 microns is about a factor of three as compared to what would be expected based on conventional plasticity theory. The incremental and non-incremental SGP theories both capture the full non-proportional loading history, including the size effect. However, they differ in their predictions of behavior in the early portion of Stage 2, due to the abrupt change in the loading path. This difference will be assessed with the aid of experimental test data.Publicationtype: Journal Article30 12 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Relationship between structure and mechanical properties in hierarchical nanoporous gold(2026); Hierarchical nanoporosity represents a novel type of material which enables the combination of mechanical stability with a reduced solid fraction. The impact of a 2nd hierarchy level on the mechanical behavior is not yet fully understood. This thesis aims to unveil the various effects of structural parameters in hierarchical nanoporous gold on the mechanical properties. Monolithic samples of hierarchical nanoporous gold (HNPG) are produced by a three-step procedure which consists of a 1st electrochemical dealloying, a coarsening step by annealing and a 2nd electrochemical dealloying. The variation of synthesis parameters enables the independent adjustment of the ligament size and the solid fraction on the upper and the lower hierarchy level. Scanning electron microscopy (SEM) as well as small- and ultra-small-angle X-ray scattering (SAXS/USAXS) are employed for the structural analysis. In preparation for SAXS/USAXS, thin walls are cut out of the bulk material by plasma focused ion beam (PFIB). Two distinct length scales are identified for hierarchical nanoporous gold. The comparison between the ligament size or diameter determined by SEM and the ligament spacing determined by SAXS/USAXS results in a conversion factor which is dependent on the solid fraction. Furthermore, the specific surface area, which is detected on the basis of the scattering intensity, shows a good agreement with the specific surface area expected from the ligament spacing. A mechanical characterization is performed by macroscopic compression tests. Coarsening on the lower hierarchy level is accompanied by a distinct decrease of stiffness and strength if the lower level solid fraction is about 0.30, which is explained by the influence of the lower level connectivity. A reduction of stiffness and strength is detected if the ratio between the upper and the lower level ligament size is reduced to about 2. The Young's modulus is lower than expected on the basis of the modified Roberts-Garboczi-law, which is associated with the early yielding of ligaments. This assumption is supported by the general impairment of the Young's modulus by the strength. During compression, the flow stress of several HNPG variants reaches the maximum value which is estimated according to the theoretical shear strength of gold and the modified Roberts-Garboczi-law. Altogether, this thesis provides a comprehensive study on the multiple interactions between structure and mechanical behavior in hierarchical nanoporosity.Publicationtype: Doctoral Thesis50 25