Acta Materialia最新文献

Despite great advances in the fabrication methods of metal nanoparticles with various sizes and shapes, the available tools for manipulating their microstructure and morphology still remain limited. In the present work we introduce the age-old metallurgical technique of recrystallization to the synthesis of metallic nanoparticles. We uniaxially compressed a large number of single crystalline and defect free Pt nanoparticles obtained by solid-state dewetting and annealed them at the temperature of 1000 °C. Our findings reveal that, while the as-dewetted particles exhibited similar shapes and crystallographic orientations, the plastic deformation and annealing led to a diverse range of shapes, microstructures, and orientations among the particles. We categorized the particles into four distinct types based on their appearance: slanted, terraced, “Danish pastry”, and broken particles. Finally, we propose a differentiation mechanism responsible for this diversification, which relies on a combination of recrystallization, surface step formation, and solid-state dewetting processes.

Pseudocapacitive storage of Zn²⁺ in nanostructured molybdenum disulfide (MoS₂) is expected to break through the limitations of sulfide in monovalent or multivalent ions storage; however, the deficiency of theoretical guidance and experimental strategies that enable rational design of MoS₂ as a kind of cathode material towards aqueous zinc-ion batteries. Herein, we firstly establish guiding theory in order to design pseudocapacitive MoS₂-based cathode in the light of the first-principles calculation, and then propose a simple and effective one-pot template-free solvothermal method to synthesize 1T phase-dominated MoS₂ cathode with low crystallinity. Through this method, MoS₂ cathode delivers an exceptional reversible capacity of 233 mAhg⁻¹ at 0.05 A g⁻¹, especially at 0.1 A g⁻¹, the stability can achieve >150 cycles, and maintains 84 % capacity retention after 2100 cycles at 5 A g⁻¹. Experimental and theoretical analysis show that such extraordinary pseudocapacitive contribution determines by the synergistic effects in the activated and stable metallic phase, abundant lattice defects and larger interlayer spacing in the rag-like MoS₂ cathode. The revealed origin of highly pseudocapacitive Zn²⁺ storage and design principle for MoS₂-based cathode facilitate the design of a variety of efficient cathodes.

The optimization of thermoelectric (TE) properties in TE materials requires controlling intrinsic factors such as order/disorder in crystal and chemical structures. Although heterogeneous interfaces play a key role in regulating TE properties, the corresponding atomic disorder-order has been ignored in composited systems. We demonstrate examples of GeTe/SnTe compositing for tuning CuInTe₂ TE properties. Evidences of increased short-range order and nanoclusters with local chemical order are presented via synchrotron X-ray pair distribution function and scanning transmission electron microscopy. Specifically, GeTe/SnTe compositing within CuInTe₂ enhances short-range order. Nanodomains of CuInTe₂(GeTe)_x are accompanied by a significant atomic-intensity fluctuation that intensifies the scattering of phonons. In contrast to CuInTe₂(GeTe)_x, nanoclusters with local chemical order are observed in CuInTe₂(SnTe)_y, accompanied by a weak atomic-intensity fluctuation, which provides superior carrier transport channels and power factor for CuInTe₂(SnTe)_0.01. Ultimately, a maximum thermoelectric figure of merit zT of ∼1.0 is reported for CuInTe₂(SnTe)_0.01, which is 54 % greater than that of pristine CuInTe₂, and higher than the 0.86 for CuInTe₂(GeTe)_0.01. This work demonstrates new disorder-order insights that reveal the mysterious roles of compositing for tuning TE transport.

Ordered interstitial complexes (OIC) are in the intermediate state between random interstitial solutes and chemical compounds, which can effectively improve the mechanical performance of multi-principle element alloys. Nevertheless, experimentally observing the complex atomic details of OIC formation and their interaction with dislocations remains challenging. Meanwhile, simulations of the OIC behavior faced the dilemma of lacking interatomic potentials for multi-component systems. In this work, we investigate the oxygen OICs in TiNbZr medium entropy alloys as a typical example to elucidate the strengthening and toughening mechanisms of OICs with a developed highly accurate deep learning potential. The formation mechanism, atomic packing of OICs and their interaction with dislocations, were then elucidated by molecular dynamics simulations with the developed potential. The interstitial atoms were found to aggregate energetically and increase the barrier of dislocation movement upon loading. It was found that the Nb content exerts a significant influence on the morphology and distribution of OICs. The decrease of Nb content favors the formation of larger cluster-like OICs. The existence of OICs can remarkably enhance the critical shear stress required for continuous dislocation movement. A pinning-cutting behavior was observed when an edge dislocation encounters an OIC, while a cross-slip behavior occurred when a screw dislocation encounters an OIC. The developed interatomic potential provides a valuable tool for elucidating the deformation mechanisms of TiNbZrO alloys, which highlights the significant effects of OICs on the mechanical performance of multi-principle element alloys.

Oxygen-deficient cerium oxide ceramics exhibit an anomalously high electromechanical response called giant electrostriction. This feature has been linked to the polarization and reorganization of ionic defects, i.e., $V_O^{··}$, under an electric field. However, the exact mechanism and how it is related to intrinsic/extrinsic characteristics of doped ceria remains unclear. The present work investigates how alkaline-earth dopants with different defect–dopant interactions affect the overall electrochemical properties and defect chemistry and, ultimately, how these features impact the final electromechanical properties. We found higher dopant–defect associations attenuate the low-frequency relaxation of the electrostrictive coefficient. The defect chemistry is shown to be the main factor controlling the final electromechanical properties rather than defect concentration. All compositions show a similar electrostrictive response at high frequencies, indicating a common underlying mechanism. All samples showed a high electrostrictive coefficient (up to 3·10⁻¹⁷ m²/V²) and pseudo-piezoelectric response (32 pm/V).

Oxides with low O²⁻ lattice diffusion rate are critical for the development of topcoat materials for next generation thermal barrier coatings (TBCs) working at > 1600 °C to prevent the fast growth of thermally grown oxide (TGO) at the bondcoat/topcoat interface. Here we delve into a comprehensive analysis of the oxygen ion transport characteristics of the recently developed low-, medium- and high-entropy rare earth tantalates (RE₃TaO₇) for TBCs by a combination of impedance spectroscopy, ¹⁸O isotope diffusion tests and atomic-scale simulations. Results show that the RE₃TaO₇ series display remarkably low oxygen ion diffusion rate (> 3 orders of magnitude lower than the state-of-the-art topcoat material yttria stabilized zirconia, YSZ) despite the presence of abundant oxygen vacancies in the structure. Molecular dynamic (MD) simulations combined with first principles calculations reveal that oxygen ions are strongly trapped by the potential well at the Ta-Ta edge in the tantalates. In addition, the high electrostatic potential (EP) surrounding oxygen vacancies and the high diffusion barriers between rare earth elements also impede oxygen ion diffusion. With low oxygen ion diffusion rate, along with exceptional thermal and mechanical properties reported previously, RE₃TaO₇ are promising topcoat materials for next-generation TBCs working at higher temperatures. Moreover, this study also provides valuable insights for understanding the O²⁻ lattice diffusion behaviour in RE₃TaO₇ with a defective fluorite structure, which may benefit the exploration of oxide-ion conductors.

In this study, the sigmoidal kinetics of deformation-induced martensitic transformation (DIMT) in the transformation-induced plasticity (TRIP)-assisted alloys, including metastable high-entropy alloys (HEAs), austenitic stainless steels, and advanced high-strength steels (AHSSs) such as low-alloyed TRIP steels, medium-Mn steels, and quenching and partitioning steels, were studied using various models. To tune mechanical stability, the influences of stacking fault energy (SFE), chemical composition, austenite grain size, deformation temperature, strain rate, and stress state were considered. The novel Fe₄₇Co₃₀Cr₁₀Ni₅V_8-xSi_x (x = 3, 4, and 6 at.%) alloys were the main investigated HEAs in the present work, in which silicon addition effectively led to lowering SFE and faster DIMT kinetics by promoting the formation of body-centered cubic α΄-martensite. The Olson-Cohen, Guimaraes (based on Johnson-Mehl-Avrami-Kolmogorov analysis), Shin, and Ahmedabadi models were analyzed and critically discussed. Moreover, a Hill-based sigmoid model was formulated as f_α' / f_sat = 1 – p / (p + ε^q) with the parameters p and q characterizing the stability of austenite, and f_sat representing the saturated volume fraction of α΄-martensite. It was demonstrated that χ = p × q can be considered the sole austenite stability parameter. It was concluded that the proposed Hill-based model, demonstrating the highest accuracy among the studied models, can effectively simulate the kinetics of α΄-martensite formation.

Accurately predicting dendrite growth during alloy solidification is crucial for enhancing the quality of metallic products. Recently, data assimilation has emerged as a promising tool for integrating two cutting-edge methods for studying dendritic growth, viz. in situ X-ray observation experiments and phase-field (PF) simulations, to elucidate important parameter(s) of the simulation and produce a “digital twin” of a growing dendrite. This study was conducted to evaluate the performance of a data assimilation system, employing an ensemble Kalman filter, through systematic twin experiments focused on columnar dendrite growth in a thin film of a binary alloy. The results show that the data assimilation system effectively estimates multiple parameters and dendrite morphology simultaneously. Furthermore, two approaches—domain decomposition method and parameter estimation method from a part of the domain—to reduce computational costs are investigated. Both methods can effectively reduce the computational cost of data assimilation. Additionally, data assimilation using voxel observation data of varying resolutions, mimicking actual X-ray images, is performed. The study findings discourage the direct use of voxel data owing to incompatible PF simulations. PF relaxation computation is explored as a solution for generating observation data with smooth PF profiles. The results show that while relaxation computation enhances the estimation accuracy for high-resolution voxel data, its efficacy diminishes for low-resolution data. These detailed investigations of data assimilation provide valuable insights for utilizing actual in situ X-ray observation data in dendrite growth studies.

The LaNbO₄-based materials were well documented to be good ionic conductors with the charge carriers of protons or interstitial oxygen ions. Herein, for the first time, we reported that the high oxide ion conduction, e.g. 3 × 10⁻³ S cm⁻¹ at 900 °C, mediated by oxygen vacancies was achieved in LaNbO₄ via equimolar Ga and Mo co-doping on the Nb site. Such a co-doping effectively stabilize the high temperature tetragonal structure of LaNbO₄ to room temperature, and thus represents the first case of room temperature tetragonal LaNbO₄ with high oxygen vacancy concentration, in contrast with the previously reported tetragonal LaNbO₄ stabilized by isovalent doping free of oxygen vacancies or donor-doping with interstitial oxygen. The local structure and conducting mechanism of oxygen vacancy defects were thoroughly studied by computational simulations. The results revealed that the oxygen vacancy was accommodated by transforming two neighboring isolated NbO₄ tetrahedrons into a corner-sharing Nb₂O₇ unit, and the oxygen ion migrated via a cooperative process involving the breaking and reforming of Nb₂O₇ units, assisted by synergic rotation and deformation of other neighboring NbO₄ tetrahedra. These findings provided us a more comprehensive understanding for the LaNbO₄-based materials and emphasized the possibility of developing LaNbO₄ material as oxide-ion conductors mediated by high concentration of oxygen vacancies.

Grain boundary types and local boundary curvatures are generally considered to be important microstructural factors controlling grain boundary migration during grain growth. In this work, grain growth in thin copper foils is studied during annealing at a temperature of 1040 °C near the melting point by ex-situ experiments and Monte Carlo simulations. Few grains, stimulated by slight deformation at the sample edge, are observed to grow abnormally into the cube-oriented recrystallized microstructure with columnar grains spanning the foil thickness. The grain boundaries of these abnormally growing grains and the grain sizes in the adjacent polycrystalline recrystallized regions are analyzed. The experimental results suggest that spatial heterogeneities in the distribution of small recrystallized grains have a significant effect on the migrating boundaries. Potts model simulations confirm that grain boundary segments with small grains in front are more likely to migrate than segments facing coarser grains. The simulations also demonstrate the importance of grain morphology. Altogether, this work highlights the effects of a heterogeneous recrystallized microstructure on abnormal grain growth in thin foil samples.