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Item type:Publication, Access status: with files , Double-tough and ultra-strong ceramics: leveraging multiscale toughening mechanisms through Bayesian optimization(Elsevier, 2026-01-13); ; ; An optimization-driven approach is presented to create a “double-tough” ceramic. The material features two main toughening mechanisms – crack deflection in a brick-and-mortar microstructure, and transformation toughening in the mortar – and it is engineered to achieve high strength and fracture toughness levels simultaneously. The material design involves high-strength alumina bricks interconnected via a ceria-stabilized zirconia mortar. Given that the design of the optimal material, featuring multiscale toughening mechanisms, typically requires a laborious trial-and-error approach, a Bayesian optimization framework is proposed to streamline and accelerate the experimental campaign. A Gaussian process is used to emulate the material’s mechanical response, and a cost-aware batch Bayesian optimization is implemented to efficiently identify optimal design process parameters, accounting for the cost of experimentally varying them. This approach expedites the optimization of the material’s mechanical properties. As a result, a bio-inspired all-ceramic composite is developed, exhibiting an exceptional balance between bending strength (704MPa) and fracture toughness (13.6MPam<sup>0.5</sup>), along with a stress intensity factor at crack initiation of 6.7MPam<sup>0.5</sup>. The material exhibits significantly higher strength than both nacre-like ceramic composites and transformation-toughened zirconia at comparable toughness levels.Publicationtype: Journal Article22 27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Microstructure and orientation effects on microcompression-induced plasticity in nanoporous goldUnderstanding the plastic deformation of nanoporous metals requires a detailed examination of their smallscale microstructural features. In this work, we present a computational study of micropillar compression in single crystal nanoporous gold (NPG) using crystal plasticity. This approach enables a systematic investigation of three key microstructural effects, including ligament size (50 ≤ 𝑙 ≤ 400 nm), solid fraction (0.2 ≤ 𝜑 ≤ 0.3), and initial crystal orientation ([001] and [̄111]), on the plastic response far beyond yielding. After validation against experimental data, the study reveals that, in line with the ’smaller is stronger’ trend, besides the yield strength, the strain hardening rate also increases as ligament size decreases. Moreover, the strain hardening rate follows a power-law scaling with solid fraction, similar to the yield strength. The analysis of two distinct crystal orientations presents findings contrasting with previous assumptions. While the yielding onset remains orientation-independent, as expected, an increase in the strain hardening rate emerges for the harder [̄111] orientation with continued compression. An effect that becomes more pronounced with increasing solid fraction and decreasing ligament size. Under these conditions, harder orientations also amplify local stress heterogeneity. Notably, the stress distribution in NPG is nearly twice as wide as that observed in the single crystal bulk material (𝜑 = 1.0). Compared to the crystal plasticity approach, traditional isotropic plasticity predicts more uniform local stress fields.Publicationtype: Journal Article41 52 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Scaling behavior of Poisson's ratio in hierarchical nanoscale network materialsHierarchical nanoscale network materials have gained increasing interest over the last decade attributing to their enhanced functional and mechanical performance, combined with reduced density. However, investigations into their Poisson's ratio, a key fundamental mechanical property, remain lacking. In this work, monolithic hierarchical nanoporous gold with tunable structure size and solid volume fraction were prepared via a two-step electrochemical dealloying method. By using in-situ digital image correlation technique, we measured their elastic and plastic Poisson's ratios during macroscopic compression. The effects of solid fraction, upper level ligament size and strain were explored systematically. We found that both the elastic and plastic Poisson's ratios are independent of the upper level ligament size and compressive strain. Notably, we introduced a novel scaling law of elastic Poisson's ratio with solid fraction in hierarchical nanoscale network materials and verified it experimentally. This study addresses a knowledge gap in the mechanics of hierarchical nanoscale network materials, offering a comprehensive understanding of their structure–mechanical property relationships. This insight provides a foundation for the design of novel materials and the optimization of their functional and mechanical properties.Publicationtype: Journal Article42 27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Machine learning pipeline for structure–property modeling in Mg-alloys using microstructure and texture descriptorsIdentifying the relationships between material structure and mechanical properties has been crucial for accelerating the exploration of the material design space for advanced alloys. However, traditional approaches for magnesium (Mg) alloys often fall short in providing quantitative and broadly applicable structure–property linkages. To address this challenge, a comprehensive machine learning pipeline is presented for structure–property modeling in extruded Mg-alloys, leveraging both microstructure and texture descriptors derived from experimental data. The pipeline encompasses a robust workflow for data extraction from optical microscopy and X-ray diffraction, advanced image processing and deep learning techniques for microstructure binarization and grain statistics, and the computation of statistical descriptors including n-point spatial correlations, gram matrices for microstructure, and generalized spherical harmonics (GSH) for texture. Dimensionality reduction techniques such as principal component analysis (PCA), isomap, and autoencoders are employed to manage the high-dimensionality of the descriptor space. Subsequently, non-linear regression models—Gaussian Process, XGBoost, and Multi-Layer Perceptron regressors—are evaluated to predict mechanical properties, specifically strain hardening exponent (n) and yield stress (σy). Our results demonstrate that XGBoost consistently outperforms other regressors, achieving a notably low mean absolute percentage error (MAPE) of 6.67% for strain hardening exponent and 7.01% for yield stress, using a combination of PCA-reduced 3-point spatial correlations and isomap-reduced gram matrices as microstructure descriptors, and isomap-reduced GSH coefficients as texture descriptors at a 150μm length scale. Shapley Additive exPlanations (SHAP) analysis further reveals that texture descriptors and aspect ratio distribution are the most influential features in predicting mechanical properties. This established ML framework for structure–property modeling in Mg-alloys, surpasses state-of-the-art benchmarks and provides a valuable template for materials design and discovery.Publicationtype: Journal Article21 36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , How peritectic melting forms bicontinuous microstructuresFine-scale porous or bicontinuous microstructures may be prepared by liquid-metal dealloying (LMD). Reverse peritectic reactions, and specifically the peritectic melting of TiAg, have been proposed as dealloying-like processes that produce quite similar microstructures but avoid the restrictions on sample size inherent in LMD. Here, studies of the microstructure evolution during peritectic melting of TiAg suggest a formation mechanism that is not LMD-like but rather relies on the migration of liquid films. The process starts with wetting of the TiAg grain boundaries by the alloy melt. Successively, both Ti and Ag continue to dissolve from one side of the wetted boundary, while β-Ti deposits on the opposite side and the liquid film sweeps the pristine TiAg crystal. TiAg-Ti interfaces with well-defined orientation relationship and with concentration gradients support this picture, as does the phase morphology in partially decomposed samples. The process generates a bicontinuous structure with a solid Ti skeleton, interpenetrated by the Ag-rich melt. The bicontinuity is conserved even after coarsening. Upon quenching, the Ti phase transforms to α-Ti. This study clarifies the mechanism of peritectic melting in TiAg, and it may provide a basis for identifying other alloy systems suitable for producing bicontinuous microstructures by that process.Publicationtype: Journal Article19 13 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Effects of structural hierarchy and size on mechanical behavior of nanoporous goldNanoporous gold with a hierarchical structure has prospects as an advanced functional material with enhanced mechanical properties, but how the hierarchical structure affects its mechanical properties compared to a unimodal structure has not been revealed. Here, we investigate the mechanical behavior of hierarchically-structured nanoporous gold and unimodally-structured nanoporous gold with the same relative density by micropillar compressive tests in dry and electrolyte environment. The ligament size at the upper-level structure in hierarchically-structured nanoporous gold and the ligament size in unimodally-structured nanoporous gold are kept similar, while having hierarchically-structured samples with ligament sizes of 10 to 50 nm at lower-level structure. We find that hierarchically-structured nanoporous gold shows greater compressive strength and pronounced stress-variation by oxidization of the surface compared to unimodally-structured nanoporous gold. A ligament-size dependency on the lower-level structure in hierarchical samples is observed, with compressive strength and stress variation by surface oxidation increasing as the lower-level ligament size decreases. Three-dimensionally reconstructed structure analysis suggests that the enhanced mechanical properties of hierarchically-structured nanoporous gold are attributed to the better-connected network of ligaments originating from two separated dealloying-coarsening procedures. The influence of dislocation activities depending on characteristic sizes is also discussed to elucidate the distinguished mechanical behavior.Publicationtype: Journal Article30 37 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Effect of Gd solutes on the micromechanical response of twinning and detwinning in Mg(2023-10-01); ; ; ; An investigation of the effect of solutes on the migration of a single {101¯2} Gd decorated twin boundary in a Mg-4wt.% Gd binary alloy in terms of the corresponding stress-strain response and the defect structure in the wake of (de)twinning was undertaken in this work. The results were benchmarked against those of a pure Mg sample that was tested under same conditions. We established that the critical stresses for both twinning and detwinning increased by 29% and 10%, respectively, due to the addition of Gd. We showed that the latter is mediated by the pinning effect of Gd atoms that decorated the pre-existing twin boundaries in the alloy. Conversely, a 68% decrease in the detwinning stress was recorded in pure Mg. We attributed the decrease to the nucleation-free nature of detwinning along with the absence of solutes atoms at the pre-existing twin boundaries. Unlike previous investigations, the work does not just highlight how twinning and detwinning affects the concurrent slip activity in pure Mg and Mg alloys, it establishes a direct link between these activities and the magnitude of the observed mechanical response.Publicationtype: Journal Article18 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Metrics for the characteristic length scale in the random bicontinuous microstructure of nanoporous goldNanoporous gold (NPG) made by dealloying exemplifies materials with random bicontinuous microstructures that can be approximated by leveled-wave type models. As a distinguishing feature, the characteristic length scale – often quantified by the “ligament size” L – of NPG may be tuned over several orders of magnitude while the microstructural geometry retains a high degree of self-similarity. It is therefore essential to have at hand accurate procedures for determining the size by experiment and to match it to analogous size metrics of model scenarios. Working with a set of NPG samples of widely different size, we compare ligament size distributions determined by analysis of scanning electron micrographs to those of the leveled-wave model. The model is representative of various material types with random bicontinuous microstructures. The size distribution is remarkably uniform over the cross-section of experimental samples. Furthermore, the distribution evolves self-similarly upon coarsening, and the normalized distribution width agrees closely to that of the model. A measure for size determined by the electrochemical capacitance ratio method correlates well with L. This supports a protocol for converting between the two measures. As a dimensionless factor characteristic of the microstructural geometry of random dual phase microstructures, the product of L and the specific surface area is found consistent between experiment and model. The findings suggest conversion factors between the various metrics, and they advertise the combination of NPG and the leveled-wave model as a showcase for characterizing the characteristic length scale of random bicontinuous microstructures.Publicationtype: Journal ArticleScopus© Citations 1 32 71 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Phase decomposition in nanoporous Au-PtThis study explores microstructure and phase decomposition in nanoporous Au-Pt made by dealloying. The starting alloy, Ag75Au12.5Pt12.5, forms a uniform solid solution. Removing the Ag by dealloying at room temperature forms nanoporous equimolar Au-Pt with a ligament size as small as 4 nm. That alloy's composition is in the Au-Pt phase diagram's regime of spinodal instability. Surprisingly, in view of the instability and of the substantial atomic rearrangements accompanying dealloying, X-ray diffraction and transmission electron microscopy reveal a homogeneous single-phase state in the bulk of the nanoporous material. This can be traced back to enrichment of Pt at the surface, which depletes the bulk in Pt. The Pt-depleted bulk is in the metastable region of the alloy phase diagram, between the binodal and the spinodal. Annealing prompts curvature-driven coarsening by diffusion, diminishing the number of sites for Pt surface segregation. The ensuing enrichment of the bulk in Pt is accompanied by the formation first of crystallographically coherent, Pt-rich regions and later of semi-coherent regions of the Pt-rich phase. The morphology of the coherent regions is compatible with spinodal decomposition. Yet, the microstructure evolution pathway is nonstandard, since decomposition here concurs with rapid coarsening of the porous microstructure. Among the prospect of the nanoporous alloy are its high kinetic stability and the opportunity to tune the surface composition through the annealing temperature.Publicationtype: Journal ArticleScopus© Citations 5 50 482 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Giant compliance and spontaneous buckling of beams containing mobile solute atomsRecent experiments have shown that the elastic compliance of a porous metal can be substantially enhanced when mobile solute is alloyed into interstitial sites of the crystal lattice. The observations agree with predictions – due to Gorsky and to Larché and Cahn – for the elasticity of open systems in which the elastic responses is probed at constant chemical potential. The underlying mechanism involves an exchange of solute between tensile and compressive fibers in beam-like elements of the microstructure. Here, we analyze the elastic deformation of such elements in a continuum approach, accounting explicitly for the coupling between chemistry and mechanics. We consider a regular solution with linear elasticity in the limit of constant composition and with a linear composition-strain coupling. Materials parameters are matched to experiments on Pd-H, so as to realistically account for the balance between chemical and mechanical energies. At constant chemical potential, the elastic response can be strongly nonlinear. With decreasing temperature, the bending goes from a monotonic moment-curvature relation to one including a horizontal tangent and, hence, a state of giant bending compliance. Reducing the temperature further brings first a temperature interval with a simple bistability and finally one with degeneracy including – depending on the chemical potential or on the mean solute fraction – the possibility of finite curvature at zero moment. Quenching the uniform solution into a two-phase region of the alloy phase diagram can lead to spontaneous buckling at no load. Furthermore, degenerate moment-curvature relations allow for bending states in which the radius is not a constant along the beam axis. Intervals of lar ge strain at constant load are similar to superelasticity, but the underlying phase transformation is here not martensitic.Publicationtype: Journal ArticleScopus© Citations 1 82 369