Nanograin Boundaries Research Articles

Ultralow thermal conductivity in Si–Ge nanograin mixtures: A cost-effective granular material for thermoelectric applications

This paper presents a theoretical study of the thermal conductivity of Si–Ge nanograin mixtures using a multiscale computational methodology based on solving the Boltzmann transport equation for phonons with first-principles techniques. A size-dependent correction factor is developed to account for the spatial dependence of the phonon distribution function on nanograin size, with parameters derived from the phonon properties of infinite Si and Ge crystals. This approach makes it possible to accurately calculate the thermal conductivity within a single nanograin, using force constants obtained from first-principles calculations. Thermal energy transport by phonons across grain boundaries is modeled by accounting for phonon transmission by two-phonon processes, weighting specular, and diffuse transmission for each phonon mode as a function of the root-mean-square roughness of the boundary relative to the phonon wavelength. The boundary thermal conductance model, previously validated against experimental data, is implemented using first-principles techniques. This approach excludes specular transmission for phonon modes with specific symmetries while ensuring conservation of the total number of modes in each symmetry class. The study examines the influence of grain size, nanograin mixture composition, temperature, and boundary asperities on the thermal conductivity of nanograin mixtures.

In-situ study on the differential evolution of He bubbles in the multilayer oxide of Fe9Cr1.5W0.4Si F/M steel corroded in lead-bismuth eutectic

The combined effects of corrosion and irradiation on nuclear components have been an important but not yet fully revealed topic. Here, the irradiation behavior of the oxide scale formed on F/M steel after lead-bismuth corrosion was in-situ investigated during He+ irradiation. The results showed that the oxide scale included a Fe3O4 outer oxide layer, a nanograin Fe(FexCr2-x)O4 spinel inner oxide layer, and an internal oxide layer. He bubbles formed in Fe3O4, Fe-Cr spinel and F/M steel were polygon, irregular elongated pores and small spheres, respectively. These differences were attributed to variations in defect generation, migration, and corrosion-induced crystal defects in different oxides. Numerous corrosion-induced nanograin boundaries and vacancies in Fe-Cr spinel exhibited more effective absorption of irradiation-induced defects. Moreover, rhombic perfect dislocation loops were detected in Fe3O4 at the late stage of irradiation, their relative positional relationship with He bubbles indicated a potential interaction between bubbles and loops.

Influence of crystallite size and impurity density on the grain structure evolution of electroplated copper films during thermal and laser annealing

In this paper, the changes in microstructure and conductivity of the films before and after thermal and laser annealing are observed, which corresponds to various combinations of crystallite sizes and impurity densities. The results show that the impurities promote grain boundary migration at larger initial crystallite sizes, which contradicts previous reports. This is because the rate of grain growth is determined by the driving force and resistance to grain growth, the former provided by the energy of grain boundaries and the impurities outside the nanograin boundaries, and the latter by the impurities enriched within the boundaries. Additionally, laser annealing is more effective than thermal annealing in stimulating impurity diffusion, resulting in a reduced influence of impurities on grain growth.

Dynamic Evolution of Copper Nanowires during CO2 Reduction Probed by Operando Electrochemical 4D-STEM and X-ray Spectroscopy.

Nanowires have emerged as an important family of one-dimensional (1D) nanomaterials owing to their exceptional optical, electrical, and chemical properties. In particular, Cu nanowires (NWs) show promising applications in catalyzing the challenging electrochemical CO2 reduction reaction (CO2RR) to valuable chemical fuels. Despite early reports showing morphological changes of Cu NWs after CO2RR processes, their structural evolution and the resulting exact nature of active Cu sites remain largely elusive, which calls for the development of multimodal operando time-resolved nm-scale methods. Here, we report that well-defined 1D copper nanowires, with a diameter of around 30 nm, have a metallic 5-fold twinned Cu core and around 4 nm Cu2O shell. Operando electrochemical liquid-cell scanning transmission electron microscopy (EC-STEM) showed that as-synthesized Cu@Cu2O NWs experienced electroreduction of surface Cu2O to disordered (spongy) metallic Cu shell (Cu@CuS NWs) under CO2RR relevant conditions. Cu@CuS NWs further underwent a CO-driven Cu migration leading to a complete evolution to polycrystalline metallic Cu nanograins. Operando electrochemical four-dimensional (4D) STEM in liquid, assisted by machine learning, interrogates the complex structures of Cu nanograin boundaries. Correlative operando synchrotron-based high-energy-resolution X-ray absorption spectroscopy unambiguously probes the electroreduction of Cu@Cu2O to fully metallic Cu nanograins followed by partial reoxidation of surface Cu during postelectrolysis air exposure. This study shows that Cu nanowires evolve into completely different metallic Cu nanograin structures supporting the operando (operating) active sites for the CO2RR.

Facile enrichment of sulfur-modified copper nanograin boundaries for efficient CO2 electroreduction and Zn-CO2 battery

Generating formic acid/formate (HCOOH/HCOO−) through renewable electricity-powered carbon dioxide reduction reaction (CO2RR) presents an appealing prospect for realizing a carbon-neutral energy cycle. Among various catalysts, sulfur-modified copper (S-Cu) stands out as potential catalysts due to their favorable attributes of high activity and especially earth abundance. However, the development of facile and energy-efficient methods for preparing S-Cu catalysts remains a great challenge. Additionally, there is still a lack of effective strategies to optimize their performance toward CO2RR. Herein, we present a facile and energy-saving method to fabricate a novel S-Cu precursor. After electrochemical activation, the precursor is converted into an S-Cu nanostructured catalyst, featuring a substantial abundance of nanograin boundary sites. This characteristic contributes to an outstanding CO2RR performance toward HCOO−, surpassing most recently reported counterparts. In situ characterizations together with control experiments disclose that the nanograin boundaries of S-Cu catalysts favor the formation of the *OCHO intermediates, while suppressing hydrogen evolution, ultimately boosting HCOO− production. Thus, the enhanced activity stems from the enrichment of nanograin boundary sites which are expected to be a common feature of advanced catalysts to achieve high HCOO− production. Moreover, when the as-prepared S-Cu catalyst is assembled as the cathode in a Zn-CO2 battery, a power density of 1.10 mW cm−2 is achieved, along with an impressive stability exceeding 250 h. This work presents a facile approach for preparing outstanding catalysts and also sheds a new light on optimizing the performance for CO2 electroreduction to HCOO−.

A simple in-situ PZT oxide's decomposition: Realizing synergistic tailoring of electrical and thermal transport properties of BiCuSeO thermoelectric ceramics through band and phonon engineering

BiCuSeO, an oxide thermoelectric material with a superlattice structure, presents the advantages of affordability, low toxicity, and environmental friendliness. However, its intrinsic low electrical conductivity has impeded its possible applications. To address this challenge, we put tiny PbZr0.52Ti0.48O3 (PZT) with varying weight percentages (x = 0, 5, 7, 9, 11) into BiCuSeO (BCSO) to fabricate thermoelectric nanocomposites. Through the spark plasma sintering process, PZT particles underwent in-situ decomposition, generating nano-sized second phases such as PbO2, TiO2, and PbZrO3, which are homogenously distributed within BCSO matrix (validated by XRD and TEM). The introduced PbO2, TiO2, and PbZrO3 second phases served a dual purpose: inhibiting the grain growth of BCSO and introducing additional nano-grain boundaries. This resulted in more effective phonon scattering sites, thereby reducing lattice thermal conductivity. Simultaneously, the Pb element derived from PZT decomposition was doped into the Bi site of the BCSO matrix, causing a reduction in the band gap of BCSO from 0.49 eV to 0.388 eV and a significant increase in carrier concentration. Consequently, this doping enhanced the electrical conductivity of BCSO-based composites, with the composite with 11 wt% PZT additive amount exhibiting a remarkable 318-fold increase, reaching 550 S/cm compared to pristine BCSO. Notably, the composite with 7 wt% PZT additive amount achieved an exceptionally low lattice thermal conductivity of 0.333 W m−1 K−1 at 823 K. Through the synergistic optimization of electrical and thermal transport properties, the BCSO-based composite with 7 wt% PZT additive amount obtained a ZT value of ∼0.9 at 873 K, representing a 2.45-fold increase compared to pristine BiCuSeO. This straightforward method presents a cost-effective and scalable approach to enhance the thermoelectric performance of various materials, opening new avenues for potential commercial applications.

Enhanced strength-plasticity synergy of 304 stainless steel by introducing gradient nanograined single austenite phase structure via USRP and induction annealing

The drawback of low strength of 304 stainless steel could be overcome by fabricating gradient nanostructures (GNS). However, deformation-induced martensite results in magnetic generation and plasticity degradation. In this work, a single austenitic GNS 304 stainless steel is fabricated by first creating a dual-phase GNS through the ultrasonic surface rolling process (USRP), followed by rapid induction heating. The yield strength of the single austenite GNS (520 MPa) is 1.68 times higher than that of the homogeneous coarse-grained structure (310 MP) without sacrificing plasticity (elongation of 65 %). Quantitative calculations indicate that fine grain, dislocation, twinning, and back-stress strengthening contribute to the strength increment by 30 %, 17.5 %, 23.4 %, and 29.1 %, respectively. Coarse-grained regions deform mainly through FCC-HCP-BCC martensitic transformation, whereas the subsurface layer forms stacking faults and twins due to increased stacking fault energy caused by the reduction in grain size. At the topmost layer, the stress required to activate dislocations is lower than that for twinning. Under high-stress conditions, martensite forms along the nanograin boundaries via a phase transition from FCC to BCC. Consequently, the excellent plasticity of the single austenite GNS stems from the synergistic effects of high back-stress hardening, TRIP and TWIP effect.

Achieving high fatigue endurance of nanocrystalline Ni/Ni-W layered composites through thermally and mechanically-induced relaxations

Stabilizing non-equilibrium nanograin boundaries has been shown to enhance the strength of nanocrystalline metals. Nevertheless, a thorough comprehension of how these stable grain boundaries impact the fatigue behavior in nanocrystalline metallic layered composites with heterogeneous interfaces is currently lacking. Here, aiming to develop high-performance small components in microelectromechanical systems, we prepared nanocrystalline Ni/Ni-W layered composites that underwent various degrees of annealing treatment. Our results reveal that the Ni/Ni-W layered composites annealed at 200 °C exhibit significantly higher fatigue strength, surpassing that of the as-prepared composites by 40 % and the Pt-10 at.% Au alloy by 17 % which is one of the best candidates for the microelectromechanical systems switches at present. The enhanced fatigue strength is primarily attributed to the annealing-induced grain boundary relaxation and mechanically-induced structural relaxation. Grain boundary relaxation enhances the strength by improving GB stability, while the mechanically-induced structural relaxation results in the coarsening and expansion of triangular columnar grains towards the Ni-W layer during fatigue loading. As a result, the dispersive strain localized regions triggered by the triangular columnar grains undertook cyclic strain accumulation and weakened localized damage accumulation in Ni layers, and thus further improved the fatigue resistance. The finding of the underlying mechanisms may offer a promising approach for designing high-performance materials for microelectromechanical systems switches operating at elevated temperatures.

Enhanced precipitation hardening in nanograined CuCrZr alloy

Nanograins were induced in solid solution CuCrZr alloy by surface mechanical grinding treatment, followed by aging treatment to investigate the precipitation behavior and hardening effect of the nanograins. Experimental results showed that body-centered cubic Cr nanoparticles precipitated at nanograin boundaries accompanied with slight nanograin coarsening, yielding a considerable precipitation hardening, even twice that of coarse grains. The hardening mechanism of grain boundary nanoprecipitates in nanograins was discussed.

Oxygen vacancy modulation in interfacial engineering Fe3O4 over carbon nanofiber boosting ambient electrocatalytic N2 reduction

The oxygen vacancy modulation of interface-engineered Fe3O4 nanograins over carbon nanofiber (Fe@CNF) was achieved to improve electrocatalytic nitrogen reduction reaction (NRR) activity and stability via facile electrospinning and tuning thermal procedure. The optimal catalyst calcined at 800 ℃ (Fe@CNF-800) was endowed with abundant nanograin boundaries and optimized oxygen vacancy (Vo) concentration of iron oxides, thereby affording 37.1 μg h−1 mgcat.-1 (−0.2 V vs. reversible hydrogen electrode (RHE)) NH3 yield and rational Faraday efficiency (10.2%), with 13.6 times atomic activity enhancement compared to of that commercial Fe3O4. The interfacial effect of assembled nanograins in particles correlated with the formation of Vo and more intrinsic active sites, which is conducive to the trapping and activation of nitrogen (N2). The in-situ X-ray photoelectron spectroscopy (XPS) measurement revealed the real consumption of adsorbed oxygen when introducing N2 by the trapping effect of Vo. Density-Functional-Theory (DFT) calculation validates the promotive hydrogenation effect and elimination of hydrogen intermediate (H*) interacted with N2 transferring toward oxygen of the support. The optimal catalyst shows a lasting NRR activity at least 90 h, outperforming most reported Fe-based NRR catalysts.

Non-layered InSe nanocrystalline bulk materials with ultra-low thermal conductivity

Exploring new prototypes for a given chemical composition is of great importance and interest to several disciplines. As a famous semiconducting binary compound, InSe usually exhibits a two-dimensional layered structure with decent physical and mechanical properties. However, it is less noticed that InSe can also adopt a monoclinic structure, denoted as mcl-InSe. The synthesis of such a phase usually requires high-pressure conditions, and the knowledge is quite scarce on its chemical bonding, lattice dynamics, and thermal transport. Here in this work, by developing a facile method combining mechanical alloying and spark plasma sintering, we successfully synthesize mcl-InSe bulks with well-crystallized nanograins. The chemical bonding of mcl-InSe is understood as compared with layered InSe via charge analysis. Low cut-off frequencies of acoustic phonons and several low-lying optical modes are demonstrated. Noticeably, mcl-InSe exhibits a low room-temperature thermal conductivity of 0.6 W·m−1·K−1, which is smaller than that of other materials in the In–Se system and many other selenides. Low-temperature thermal analyses corroborate the role of nanograin boundaries and low-frequency optical phonons in scattering acoustic phonons. This work provides new insights into the non-common prototype of the InSe binary compound with potential applications in thermoelectrics or thermal insulation.

Probing Hybrid LiFePO4/FePO4 Phases in a Single Olive LiFePO4 Particle and Their Recovering from Degraded Electric Vehicle Batteries.

The recycling of LiFePO4 from degraded lithium-ion batteries (LIBs) from electric vehicles (EVs) has gained significant attention due to resource, environment, and cost considerations. Through neutron diffraction, X-ray photoelectron spectroscopy, and transmission electron microscopy, we revealed continuous lithium loss during battery cycling, resulting in a Li-deficient state (Li1-xFePO4) and phase separation within individual particles, where olive-shaped FePO4 nanodomains (5-10 nm) were embedded in the LiFePO4 matrix. The preservation of the olive-shaped skeleton during Li loss and phase change enabled materials recovery. By chemical compensation for the lithium loss, we successfully restored the hybrid LiFePO4/FePO4 structure to pure LiFePO4, eliminating nanograin boundaries. The regenerated LiFePO4 (R-LiFePO4) exhibited a high crystallinity similar to the fresh counterpart. This study highlights the importance of topotactic chemical reactions in structural repair and offers insights into the potential of targeted Li compensation for energy-efficient recycling of battery electrode materials with polyanion-type skeletons.

Nanograin-Boundary-Abundant Cu2O-Cu Nanocubes with High C2+ Selectivity and Good Stability during Electrochemical CO2 Reduction at a Current Density of 500 mA/cm2.

Surface and interface engineering, especially the creation of abundant Cu0/Cu+ interfaces and nanograin boundaries, is known to facilitate C2+ production during electrochemical CO2 reductions over copper-based catalysts. However, precisely controlling the favorable nanograin boundaries with surface structures (e.g., Cu(100) facets and Cu[n(100)×(110)] step sites) and simultaneously stabilizing Cu0/Cu+ interfaces is challenging, since Cu+ species are highly susceptible to be reduced into bulk metallic Cu at high current densities. Thus, an in-depth understanding of the structure evolution of the Cu-based catalysts under realistic CO2RR conditions is imperative, including the formation and stabilization of nanograin boundaries and Cu0/Cu+ interfaces. Herein we demonstrate that the well-controlled thermal reduction of Cu2O nanocubes under a CO atmosphere yields a remarkably stable Cu2O-Cu nanocube hybrid catalyst (Cu2O(CO)) possessing a high density of Cu0/Cu+ interfaces, abundant nanograin boundaries with Cu(100) facets, and Cu[n(100)×(110)] step sites. The Cu2O(CO) electrocatalyst delivered a high C2+ Faradaic efficiency of 77.4% (56.6% for ethylene) during the CO2RR under an industrial current density of 500 mA/cm2. Spectroscopic characterizations and morphological evolution studies, together with in situ time-resolved attenuated total reflection-surface enhanced infrared absorption spectroscopy (ATR-SEIRAS) studies, established that the morphology and Cu0/Cu+ interfacial sites in the as-prepared Cu2O(CO) catalyst were preserved under high polarization and high current densities due to the nanograin-boundary-abundant structure. Furthermore, the abundant Cu0/Cu+ interfacial sites on the Cu2O(CO) catalyst acted to increase the *CO adsorption density, thereby increasing the opportunity for C-C coupling reactions, leading to a high C2+ selectivity.

Ultra-fast amorphization of crystalline alloys by ultrasonic vibrations

• A facile and rapid solid-state amorphization method was discovered. • The tuning of amorphous content was achieved. • Ultrasonic vibration method exhibits an outstanding time advantage than other methods. • The elements redistribute uniformly and rapidly under ultrasonic vibration. • A new order-disorder transition mechanism was introduced. The amorphization of alloys is of both broad scientific interests and engineering significance. Despite considered as an efficient strategy to regulate and even achieve record-breaking properties of metallic materials, a facile and rapid method to trigger solid-state amorphization is still being pursued. Here we report such a method to utilize ultrasonic vibration to trigger amorphization of intermetallic compound. The ultrasonic vibrations can cause tunable amorphization at room temperature and low stress (2 MPa) conveniently. Remarkably, the ultrasonic-induced amorphization could be achieved in 60 s, which is 360 times faster than the ball milling (2.16 × 10 4 s) with the similar proportion of amorphization. The elements redistribute uniformly and rapidly via the activated short-circuit diffusion. Both experimental evidences and simulations show that the amorphous phase initiates and expands at nanograin boundaries, owing to the induction of lattice instability. This work provides a groundbreaking strategy for developing novel materials with tunable structures and properties.

Precipitation and its hardening behavior in an austenitic steel with different strain-induced structures

Various structures including dislocations, nanotwins, and nanograins were induced in solid solution austenitic steels by dynamic plastic deformation, followed by aging treatment to investigate their precipitation and hardening. Microstructural characterization showed that gamma prime nanoparticles are uniformly distributed in the coarse grains with high-density dislocations, but located on the twin boundaries of nanotwinned grains. Nevertheless, eta nanoprecipitates occur on the boundaries of nanograins. Surprisingly, considerable precipitation hardening of the eta nanoprecipitates was obtained in the nanograins, comparable to precipitation hardening of gamma prime nanoprecipitates in the coarse grains, which is significantly different from the deleterious effect of eta phase on strength in coarse-grained materials.

Operando studies reveal active Cu nanograins for CO2 electroreduction.

Carbon dioxide electroreduction facilitates the sustainable synthesis of fuels and chemicals1. Although Cu enables CO2-to-multicarbon product (C2+) conversion, the nature of the active sites under operating conditions remains elusive2. Importantly, identifying active sites of high-performance Cu nanocatalysts necessitates nanoscale, time-resolved operando techniques3-5. Here, we present a comprehensive investigation of the structural dynamics during the life cycle of Cu nanocatalysts. A 7 nm Cu nanoparticle ensemble evolves into metallic Cu nanograins during electrolysis before complete oxidation to single-crystal Cu2O nanocubes following post-electrolysis air exposure. Operando analytical and four-dimensional electrochemical liquid-cell scanning transmission electron microscopy shows the presence of metallic Cu nanograins under CO2 reduction conditions. Correlated high-energy-resolution time-resolved X-ray spectroscopy suggests that metallic Cu, rich in nanograin boundaries, supports undercoordinated active sites for C-C coupling. Quantitative structure-activity correlation shows that a higher fraction of metallic Cu nanograins leads to higher C2+ selectivity. A 7 nm Cu nanoparticle ensemble, with a unity fraction of active Cu nanograins, exhibits sixfold higher C2+ selectivity than the 18 nm counterpart with one-third of active Cu nanograins. The correlation of multimodal operando techniques serves as a powerful platform to advance our fundamental understanding of the complex structural evolution of nanocatalysts under electrochemical conditions.

Ag Dendrites on W/C as Enhanced Active and Stable Electrocatalysts for Scalable Solar-Driven CO2rr

The electrochemical conversion of solar energy into competent chemicals is the most efficient technique to ensure clean and sustainable energy source for society in the future. In fact, solar cells can electrochemically produce electricity without pollution by converting CO2 into a variety of chemicals. The carbon dioxide reduction reaction (CO2RR) is an environmentally friendly approach to produce useful hydrocarbons such as carbon monoxide (CO), methane, ethylene, formates, etc and alcohols and remove exhausted CO2, which is a greenhouse gas. Conventionally, studies on the CO2RR have been conducted by using liquid-phase H-cells and a CO2-saturated electrolyte. However, it resulted in a low current density because the low solubility of CO2 in the liquid electrolyte occurs mass transfer limitation. To improve of the current density related to the CO2RR, two types of gas-fed CO2RR electrolyzers containing gas diffusion layer (GDL) electrodes have been proposed. The first type of CO2RR devices use a liquid electrolyte, the electrolyte increases CO2RR performance through controlling the cathode conditions, such as pH and anion concentration. The second type of CO2RR devices is zero-gap electrolyzers that use an anion exchange membrane (AEM) and humidified CO2 gas. AEM transmits carbonate and hydroxide ion, inducing favorable environmental for CO2RR. These zero-gap CO2 electrolyzers are attracting attention as the most promising system owing to several advantages such as extremely low ohmic resistance, scalable and stackable configuration, and commercial applicability, as affirmed by using a system consisting of a fuel cell and water electrolyzer. Among the products of the CO2RR, CO is particularly attractive as aspect of its economic benefits and large demand. Ag-based materials exhibit the most electrochemical performance for producing CO. and high selectivity. To enhance the catalytic activity of Ag-based catalysts, various approaches have been studied to change the surface electronic structure of Ag such as alloy formation, anion-based modification, shape control, near-surface structure and engineering. However, catalyst designs that do not consider the gas phase reactions cannot enough utilize their catalytic activity although recent progress has made in the development of Ag-based catalysts for the CO2RR. Therefore, considerable efforts must be preoccupied with the development of highly active, stable, and gas-transferable structured catalysts for gas-fed CO2RR electrolyzers with incoporating a GDL. Additionally, aming for the realization of clean technology for producing CO, we demonstrate the practicalbility of sunlight-driven CO2RR on a large scale using commercial silicon-based solar cells and zero-gap electrolyzers. Silicon-based solar cells are still the preferred commercially applicapable options for producing large amounts of electrical power from solar energy because of their scalability. In this study, we report a 3D silver dendrite on W/C (as denoted WC@AgD) catalyst with abundant nanograin boundaries that show enhanced CO2RR performance and stability. WC@AgD exhibited marked catalytic activity with a maximum CO partial current density of 400 mA cm-2 and durability for 100 h at 150 mA cm-2. We also fabricated an solar-to-CO (STC) conversion device combined with a silicon-based solar cell of 120 cm2 area and a zero-gap CO2 electrolyzer with an area of 10 cm2. The stand-alone photovoltaic-electrochemical system achieved a solar-to-CO efficiency (ηSTC) of 12.1 % at 1A under AM 1.5 G illumination and realistic outdoor conditions. The device design and electrode configuration extended viable route for implementing large-scale installations for solar-driven production of chemicals. Figure 1

Theoretical study on the hydrogen capture and damage mechanisms of PuO2 nanograin boundary

The hydriding corrosion is harmful to the long-term storage of plutonium (Pu). Since the defect-free PuO2 overlayer has been proved to resistance hydrogen attack, Pu hydriding is mainly related to such penetrating defects as the grain boundaries (GBs) of PuO2. We perform comprehensive DFT+U-D3 calculation and tensile-test simulation to investigate the incorporation and dissolution behaviors of H in PuO2 GB, and the induced hydrogen damage. The exothermic incorporation and dissolution of H confirm the capture effect of PuO2 GB, which are contrary to endothermic behaviors of H in PuO2 bulk. The predicted saturation solubility of H demonstrates that GB is the active site that promotes H dissolution, which is one of the important factors to Pu hydriding. The dissolved H can further weaken the Pu–O bonds in GB and facilitate the intergranular fracture of PuO2 overlayer. Our study provides key mechanistic insights towards interpreting of Pu hydriding corrosion, which is critical for predictive modeling of the induction time.

High pressure suppressing grain boundary migration in a nanograined nickel

Grain boundaries (GBs) of nanograined metals are prone to migrate when subjected to mechanical loading. In this study, nanograined pure nickel samples with an average grain size of about 70 nm were deformed under pressure of 20 GPa and 43 GPa using a diamond anvil cell. It was found that the average grain size decreased slightly after high pressure compression, which meant high pressure suppressed the nanograin boundaries migration. Extensive extended dislocations with large dissociation width (averagely 5-6 nm) as well as Lomer-Cottrell locks were observed in the high pressure deformed nanograined Ni, indicating that partial dislocation activities dominated the plastic deformation, which may facilitate to relax GBs and thus suppress GBs migration. The finding of this study may help to fabricate stable nanocrystalline metals.

Kinetics and energetics of room-temperature microstructure in nanocrystalline Cu films: The grain-size dependent intragrain strain energy

The fast kinetics of the low-temperature microstructure evolution in nanocrystalline metals requires an additional driving force from the excess intragrain energy in addition to the driving forces from the grain boundary energy, surface or interface energy, and thermal strain energy. If the excess volume of the grain boundary induces lattice distortions in grain interiors, the intragrain energy is the elastic-strain energy and can be determined from a grain-size-dependent strain model. Considering the available intragrain strain energy, we use transmission electron microscopy, x-ray diffraction line-broadening analysis, and theoretical models to investigate the kinetics and energetics of room-temperature nanostructure relaxation and abnormal grain growth in electroplated nanocrystalline Cu films devoid of thermal strains and high-density dislocations. The experimental data of grain sizes and microstrains are consistent with the theoretical size-dependent strain model. The limited nanostructure relaxation of Cu occurs with the grain boundary width reduction and intragrain strain release, which cannot alter the structural anisotropy and intrinsic high-energy state of nanograins. Based on quantitative descriptions of the variations in grain size, microstrain, and transformed fraction during abnormal grain growth, the possible driving forces and grain boundary mobility were systematically evaluated. The results indicate that the size-dependent intragrain strain energy provides a crucial driving force for rapid nanograin growth and texture transition, whereas the low nanograin boundary mobility in Cu films is probably correlated with the strained-lattice migration and faceted-boundary migration.