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In this study, surface mechanical attrition treatment was employed to sucessfully produce a gradient nanostructured layer on WE43 magnesium alloy. X-ray diffraction, energy dispersive X-ray spectrometer, and high-resolution transmission electron microscope observations were mainly performed to uncover the microstructure evolution responsible for the refinement mechanisms. It reveals that the grain refinement process consists of three transition stages along the depth direction from the core matrix to the topmost surface layer, i.e., dislocation cells and pile-ups, ultrafine subgrains, and randomly orientated nanograins with the grain size of ~40 nm. Noticeably, the original Mg3RE second phase is also experienced refinement and then re-dissolved into the α-Mg matrix phase, forming a supersaturated solid solution nanostructured α-Mg phase in the gradient refined layer. Due to the cooperative effects of grain refinement hardening, dislocation hardening, and supersaturated solid-solution hardening, the gradient nanostructured WE43 alloy contributes to the ultimate tensile strength of ~435 MPa and ductility of ~11.0%, showing an extraordinary strain hardening and mechanical properties among the reported severe plastic deformation-processed Mg alloys. This work provides a new strategy for the optimization of mechanical properties of Mg alloys via combining the gradient structure and supersaturated solid solution.

The mechanical properties of complex concentrated alloys (CCAs) depend on their formed phases and corresponding microstructures. The data-driven prediction of the phase formation and associated mechanical properties is essential to discovering novel CCAs. The present work collects 557 samples of various chemical compositions, comprising 61 amorphous, 167 single-phase crystalline, and 329 multi-phases crystalline CCAs. Three classification models are developed with high accuracies to category and understand the formed phases of CCAs. Also, two regression models are constructed to predict the hardness and ultimate tensile strength of CCAs, and the correlation coefficient of the random forest regression model is greater than 0.9 for both of two targeted properties. Furthermore, the Shapley additive explanation (SHAP) values are calculated, and accordingly four most important features are identified. A significant finding in the SHAP values is that there exists a critical value in each of the top four features, which provides an easy and fast assessment in the design of improved mechanical properties of CCAs. The present work demonstrates the great potential of machine learning in the design of advanced CCAs.

The local hydrogen distribution has significant influences on hydrogen embrittlement. In this work, mode-I fractures of (010)[100] pre-cracked α-Fe single crystal containing dissolved and absorbed hydrogen atoms are simulated by molecular dynamics and the time-stamped force-bias Monte Carlo methods. Statistics show that when located near the {112} plane, hydrogen atoms accelerate cleavage fracture and suppress the slip of {112} ; when located on the {110} plane, they promote martensite transformation and increase {110} slip. Most adsorbed hydrogen atoms are concentrated near the inside of the crack surface and suppress fracture early by stress relaxation; therein concentrates stresses inside the matrix, and causes microvoid-coalescence fracture.

Deformation-induced martensitic transformations (DIMTs) have been widely observed in iron and ferroalloys under various mechanical loading conditions, thereby showing extreme scientific merits and engineering significance. Since deformations and fractures affect one another and reflect the relative movements of atoms, DIMTs often accompany fractures. In this work, molecular dynamics simulation was performed with a (010) [100] pre-cracked model to study DIMTs from an α-Fe single crystal during the mode-I fracture process. The observed DIMTs were verified using first-principle calculations. A crack tip tracking algorithm by scanning the nearby atoms is proposed, and the obtained critical stress intensity factor was proved to be close to the experimental results. Quasi-cleavage fracture happened with the nucleation and growth of the γ (fcc) phase, which was transformed by activating the {121} $$\left\langle {111} \right\rangle$$ and {110} $$\left\langle {111} \right\rangle$$ shears near the crack tip. The layered e (hcp) phase was formed by stacking faults inside the γ phase and was unstable by driving force analysis.

In this article, three-dimensional nanoporous Cu/Cu6Sn5 microparticles (3D-NP Cu/Cu6Sn5 MPs) were prepared by one-step chemical dealloying of Cu20Sn80 (at%) alloy slices in a mixed aqueous solution of HF and HNO3 and then filled into a three-dimensional porous copper foam (3D-PCF) skeleton as anode (3D-PCF@Cu/Cu6Sn5) for lithium-ion batteries (LIBs). The results show that the ellipsoidal 3D-NP Cu/Cu6Sn5 MPs with feature sizes of 3 to 8 μm are composed of numerous uniform nanoparticles (100 to 200 nm) and plenty of voids. Compared with similar Sn-based electrodes in this work and other published reports, the as-prepared electrode delivers more outstanding electrochemical performance with a superior reversible capacity of 1.90 mAh cm−2, 84.44% capacity retention and > 99.5% coulombic efficiency upon 200 cycles. The cycling stability and integrity of the overall structure of the composite electrode have been greatly enhanced under the synergistic effect of the buffer effect of copper as the inactive component, the unique hierarchical porous electrode architecture and the effective limitation in three dimensions of the 3D-PCF skeleton. We are confident that this work can provide new-generation LIBs with a promising anode candidate and a facile method of dealloying, and a subsequent filling step can achieve the practical production and application of high-performance LIBs.

Freestanding 3D nanoporous Cu-supported Cu2O hierarchical nanoplate arrays (3D NPC@Cu2O HNPAs) have been prepared in situ by facile one-step oxidation-assisted electrochemical dealloying, in which Cu2O HNPAs are characteristic of large-sized (hundreds of nm) 2D nanoplate arrays firmly embedded in small-sized (tens of nm) counterparts. The unique 3D nanocomposites as anodes for Li-ion batteries (LIBs) display superior Li storage properties involving ultrahigh specific capacity, long cycle life and excellent rate capability, which deliver a reversible capacity as high as 3.0 mAh cm−2 with 71.4 pct capacity retention after 450 long cycles at 2 mA cm−2. Even when the current density reaches 5 mA cm−2, an ultrahigh reversible capacity of 3.4 mAh cm−2 still can be achieved smoothly without obvious capacity decay after 250 cycles. It is totally comparable to or even exceeds the current level of a commercial graphite anode. The outstanding electrochemical performance can be largely ascribed to the unique 3D electrode structure comprising HNPAs and NP substrate, the large contact area between active material and electrolyte, in situ growth of active material upon the porous substrate, a compact joint of small-sized intermediate nanolayers and favorable mass transfer among vertical hierarchical nanoplates, indicative of a quite promising candidate as a binder-free integrated anode toward practical application of advanced LIBs.

Nanoscale concentration modulation (CM) is a novel and effective approach of manipulating martensitic transformations (MTs) for developing next-generation high-performance shape memory alloys (SMAs). Spinodal decomposition is one of the most economic methods to obtain bulk compositionally modulated materials for practical applications. The wavelength, amplitude, and statistical distribution of CM generated by spinodal decomposition are tunable via adjusting the aging temperature, or the aging time. However, how these features influence the effect of CM on MTs still remains largely unexplored. In this study, theoretical analyses and computer simulations are combined to dissect the influence of these features on the kinetic process of MTs and mechanical properties of SMAs. The findings of this study provide insights and guidance on the design of SMAs for desired mechanical properties via CM engineering. Moreover, the findings are applicable to not only SMAs but also other materials that have MTs, e.g. steels and high-entropy alloys.

The corrosion issue has been considered as the greatest challenge in metallic devices, which will not only degrade the performance but also cause safety concerns. Within the Blue Energy framework, the metallic electrode in nanogenerators will always face the risk of chloride attack through different approaches in the long-term applications within the extreme oceanic conditions. Here in this work, the chloride ion accumulation in the passive film that initiates from the surface adsorption via the surface defects towards the internal migration has been unravelled in our case study and analysis. The underlying chloride ion migration mechanism will be ascribed to the anion Frenkel pair-like mechanism as a defect induced energy transfer process. The molecule dynamic simulations under 300 K also support the evident damage of the passive film induced by the subtle chloride attack. The in-depth understanding of the corrosion process from a microscopic perspective can further assist for diagnosing and remediation of corrosion of the future nanogenerator electrode and other metallic devices.

Evaluating the point defect sink strength of grain boundaries is crucial for understanding the metal behavior of plasticity and damage under irradiation. In this paper, the point defect sink strength of low-angle symmetrical tilt grain boundaries is investigated by the phase field dislocation climb model under irradiation. The results indicate that sink strength of grain boundary is not only determined by the long-range point defect diffusion but also the short-range point defect absorption by the dynamic climbing of grain boundary dislocations. All of the study findings prove that the irradiation induced creep deformation of grain boundaries is essential for evaluating the radiation tolerance of materials.

A phase field (PF) model was proposed to investigate corrosion in a stressed metal. The Allen–Cahn equation, associated with the Nernst–Planck, Poisson's, and mechanical equilibrium equations, was established to govern phase transformation, ion diffusion, electric potential distribution, and mechanical deformation, respectively. The electrochemical reaction rate was expressed as a function of the electrochemical potentials of reactants and products based on a detailed balance of reactions, which conforms to a generalized Butler–Volmer relationship. The numerical results reveal that the stress concentration at the tip of a corrosion pit promote a higher corrosion rate, which leads to a sharpened tip and the accelerated failure of a metallic structure. To consider a more complicated scenario, a metal matrix composite (MMC) reinforced with inert fibers/particles was investigated. If a fixed displacement boundary condition is applied, the corrosion resistance of the MMC would benefit from the decrease in reinforcement stiffness; whereas when the MMC is under a constant load, a stiffer reinforcement would result in an increase in corrosion resistance.

Crystal structure determines the distinct deformation mode of crystalline materials and thus plays a critical role in micro-scale deformation. The micro-deformation mechanism at grain level, however, is still not well understood and the knowledge of how crystal structure affects size effect and its affected deformation behaviors in micro-scale deformation is not yet systematic and extensive enough to support micro-manufacturing and microproduct development. To explore the influence of crystal structure on size dependent deformation, strain heterogeneity and fracture in micro-scale deformation, a series of micro-scale tensile tests using polycrystalline pure copper (FCC), pure iron (BCC) and pure α-titanium (HCP) sheets with various thicknesses and microstructural grain sizes were conducted. A mechanism-based crystal plasticity (CP) model incorporating size-dependent slip and twinning was proposed. The CP model successfully predicted the influence of grain size and thickness on the flow stress as well as the dependence of twinning volume fraction on the grain size of Ti samples. Full-field simulation was carried out to thoroughly explore the influence of crystal structure on grain-scale strain heterogeneity and fracture behavior via examining strain localization, lattice rotation, slip and twinning activity. Results showed that when only few grains exist in the thickness direction, slip activation is particularly limited in HCP Ti sample, leading to strain concentration and generation of wide and long shear bands thus sharply reduce the fracture toughness. Lattice rotation of Cu samples is most uniform. The large strain in samples of BCC Fe is distributed more dispersedly and more shear bands are formed. This work presents a comprehensive understanding of the effect of crystal structure on the size effect affected micro-scale deformation of metallic materials at grain level and a basis to support the applications of micro-scale deformation for making different crystal structured micro-parts.

There is a genuine need to shorten the development period for new materials with desired properties. In this work, machine learning (ML) was conducted on a dataset of the elastic moduli of 219 bulk-metallic glasses (BMGs) and another dataset of the critical casting diameters (Dmax) of 442 BMGs. The resulting ML model predicted the moduli and Dmax of BMGs in good agreement with most experimentally measured values, and the model even identified some errors reported in the literature. This work indicates the great potential of ML in design of advanced materials with target properties.

Nanoporous materials have attracted great attention due to the large ratio of surface over volume. Similarly, nanomaterials with big surface roughness have also high surface/volume ratio. The present work investigates the electrochemical behavior of a nanowire electrode with a big surface roughness. An on-chip individually addressable suspended gold nanowire (width: 340 nm, thickness: 90 nm, and length: 5.5 μm) electrode with an arithmetic mean surface roughness of 15.02 ± 2.95 nm was fabricated by using the electron beam lithography and reactive ion etching technique. The Cyclic Voltammograms (CV) of the suspended Au nanowire electrode in both the potassium ferricyanide and the sulfuric acid electrolytes show noticeably different characteristics from that of the control Au thin film electrode. The suspended nanowire shows an excellent room-temperature cyclic reliability, with only ±3% variation in the integrated capacitance after 600 cycles at the scanning rate of 0.1 Vs-1. The facile on-chip fabrication, large effective surface area, and excellent cyclic stability make the suspended gold nanowire electrode an ideal candidate for many emerging applications such as electrochemical catalysts, biosensors, and detectors.

A phase-field model is proposed to study the inhomogeneous growth of zirconia induced by the stress–oxidation interaction, which captures the complex interplay among diffusion, oxidation kinetics, interfacial morphology evolution, and stress variation in an oxidation process. Through this numerical model, many experimentally observed but insufficiently understood phenomena can be well explained. Specifically, the numerical simulations reveal quantitatively the causes of interface roughening or smoothening during the inward oxide growth, the roughness-dependent oxide growth rate, and the nucleation sites of premature cracking. These numerical findings can be used as the theoretical references for the improving the durability of oxide scale and prolonging the service life of zirconium-based alloy cladding used in the nuclear power plant.

Structural deterioration and low conductivity are key factors that give rise to severe capacity fading of transition metal oxides as anodes for lithium-ion batteries (LIBs). An effective way to overcome this challenge is to construct nanosized metal oxide heterostructures integrated with a 3D nanoarchitectured metal matrix to buffer volume variation, reinforce structural stability and improve electronic conductivity. Herein, a facile and effective underpotential oxidation (UPO) assisted dealloying protocol has been developed successfully to synthesize freestanding monolithic 3D nanoporous copper@1D cuprous oxide nanowire network (3D NPC@1D Cu2O NWN) heterostructures. Based on their dealloying behavior, the evolution law can be well established, sequentially described as “dealloying of (Mn, Cu) accompanying Cu2O NW germination”, “growth of Cu2O NWs accompanying (Mn, Cu) re-dealloying” and “Cu2O NWN coarsening”. Compared to other CuxO-based electrode materials with different structural designs reported in the literature, the unique nanocomposites as an anode for LIBs exhibit far superior Li storage performance including an ultrahigh initial reversible capacity of 2.71 mA h cm−2, good cycling stability with 60.2% capacity retention after 150 cycles (just 0.007 mA h per cm2 per cycle for capacity fading), and excellent rate capability with reversible capacity as high as 1.64 mA h cm−2 after 55 high-rate cycles. This mainly originates from effectively accommodating huge volume changes during charge/discharge processes, providing abundant reaction active sites, shortening electron/ion transport paths, and building a reliable 3D/1D composite nano-configuration without additional binders and conductive agents, indicative of a considerably promising anode candidate for high-performance LIBs.

Surface functionalization of substrates is a promising strategy to tune thermal transport in supported graphene. In this work, we have conducted molecular dynamics simulations to investigate how the surface hydroxylation of amorphous SiO2 substrate affects heat conduction in supported graphene. The results show that the thermal conductivity of supported graphene is decreased by introducing hydroxyl groups on the substrate surface. The underlying physics of thermal conductivity suppression is explained by analyzing the phonon spectral energy density, lifetime, and participation ratio. We have observed that the surface hydroxylation decreases the phonon lifetime and causes remarkable damping of out-of-plane flexural phonons. Moreover, the hydroxyl groups induce modifications of the graphene configuration, which result in the phonon localization and, correspondingly, the low thermal conductivity. Our findings highlight the importance of the substrate surface on thermal conductivity of supported graphene and ...

In this paper, novel three dimensional hierarchical porous Sn-Ni (3D-HP Sn-Ni) alloys were investigated as a promising anode for high-performance Li ion batteries (LIBs), which was fabricated by pulse electrodeposition of mesoporous Sn-Ni alloy made of ultrafine nanoparticles on the 3D nanoporous copper substrate from chemical dealloying of as-cast Al55Cu45 (at.%) alloy slices in the HCl solution. The results show that the as-obtained 3D-HP Sn-Ni alloys are typically characteristic of open, bicontinuous, interpenetrating bimodal pore size distribution comprising large-sized (hundreds of nm) ligament-channel network architecture with highly porous channel walls (several nm). Compared to the two dimensional nanoporous Sn-Ni (2D-NP Sn-Ni) thin films, the 3D-HP Sn-Ni alloys as anode for LIBs show superior cycling stability with reversible specific capacity of 0.25 mAh cm−2 and coulombic efficiency of more than 95% up to 200 cycles. Moreover, the reversible capacity as high as 0.22 mAh cm−2 can be achieved even after a series of high-rate charge–discharge cyclings. The satisfactory electrochemical properties can be mainly ascribed to the unique 3D hierarchical porous structure, large contact surface area between active material and electrolyte, as well as good buffer effect of inactive component, which is greatly beneficial to alleviate the huge volume variation, enhance the loading mass of active material, shorten the Li+ migration distance and improve the electron conductivity. We believe that this present work can provide a promising anode candidate towards practical application of high-performance LIBs.

In micro-bending process, the size effect induced by the variation of grain size and geometrical size (the thickness) of sheet metals, represented by the ratio of surface grain number to the total grain number of workpiece (η), and strain gradient effect are the key factors affecting the bending behaviour and springback angle. The interaction of the grain-based size effect and the strain gradient effect on springback has not yet been fully understood and investigated in micro-scaled bending of metallic materials. In this research, a combined constitutive model simultaneously considering both the grain size effect and strain gradient was proposed. The theoretical calculation was conducted using the proposed model, and quantitative evaluation was made of the contribution from each kind of size effect on the springback angle. The springback angle due to strain gradient size effect decreases with the increase of sheet thickness and the decrease of the grain size. Pure microbending experiments using copper alloy sheet metal samples with the thickness of 0.1, 0.2, and 0.4 mm were conducted, and the springback angles calculated using the established model were corroborated by the experimental results, providing model validation. The reported results thus provide an in-depth understanding of the grain-geometrical size effect and strain gradient size effect influence on the springback behaviour in micro-bending of metallic materials.

Pitting corrosion is one of the most destructive forms of corrosion that can lead to catastrophic failure of structures. This study presents a thermodynamically consistent phase field model for the quantitative prediction of the pitting corrosion kinetics in metallic materials. An order parameter is introduced to represent the local physical state of the metal within a metal-electrolyte system. The free energy of the system is described in terms of its metal ion concentration and the order parameter. Both the ion transport in the electrolyte and the electrochemical reactions at the electrolyte/metal interface are explicitly taken into consideration. The temporal evolution of ion concentration profile and the order parameter field is driven by the reduction in the total free energy of the system and is obtained by numerically solving the governing equations. A calibration study is performed to couple the kinetic interface parameter with the corrosion current density to obtain a direct relationship between overpotential and the kinetic interface parameter. The phase field model is validated against the experimental results, and several examples are presented for applications of the phase-field model to understand the corrosion behavior of closely located pits, stressed material, ceramic particles-reinforced steel, and their crystallographic orientation dependence. Stainless steel corrosion can be successfully simulated using a phase field model that takes into account anodic and cathodic reactions. A team led by San Qiang Shi at the Hong Kong Polytechnic University adapted a phase field method used for simulating metallic microstructure evolution to study corrosive pit growth in stainless steel immersed in mildly salted water. The authors developed equations taking into account the transport and concentration of ionic species and introduced a parameter to describe the changing corrosion interface. The resulting model simulated the corrosion process from the meso- to the macroscale, and successfully showed that two pits can coalesce to form a wider pit, while corrosion occurred preferentially along specific crystallographic planes. Successfully simulating complex corrosion situations may help us better understand them and lessen their impact.

A quantitative phase-field model is developed for the investigation of crevice corrosion of iron in salt water. Six types of ionic species and some associated chemical reactions have been considered. In addition to the transient distributions of ion concentrations and electric potential in the electrolyte, some physical and chemical properties related to corrosion, such as overpotential, pH value and corrosion rate, under different metal potentials are studied. Benchmarking of the phase-field model against a sharp interface model is conducted. The corrosion rates predicted by the models are in the same order of magnitudes with experimental results.

The present work further develops the multi-temperature approach on load, time, and temperature-dependent deformation for indentation creep. Multi-temperature micro-indentation creep tests were carried out on nanotwinned copper (nt-Cu) at five temperatures of 22 °C (RT), 40 °C, 50 °C, 60 °C and 70 °C. In analogy with stress, hardness is used to gauge the indentation creep loading level, while the indentation depth is used to characterize the indentation creep deformation and the creep strain rate is represented by the indentation depth strain rate. The multi-temperature micro-indentation creep tests generate sufficiently large experimental data, which makes the development of a novel formula for indentation creep feasible. There are few intrinsic parameters that characterize the capability of the microstructure of a material against load, time, and temperature dependent deformation and they are the strain rate sensitivity, the athermal hardness exponent, intrinsic activation energy, and activation volume. The strain rate sensitivity is determined from isothermal creep data at one temperature, while the other parameters have to be determined from multi-temperature creep data. The novel formula is validated by the experimental data of the multi-temperature indentation creep tests on the nt-Cu. The creep mechanisms of the nt-Cu are also discussed and analyzed by using the determined values of the intrinsic parameters.

It is a longstanding notion that alloying different sized elements can cause lattice distortion and phase transition in chemically complex alloys. However, a quantitative understanding of it remains difficult for traditional alloys, and becomes even more challenging for equimolar multicomponent alloys, also known as “high entropy alloys”, which recently emerged as a promising structural/functional material and have been attracting tremendous research interest due to their unique properties. In this work, we carried out extensive first-principles calculations on a series of equimolar complex alloys with a chemically disordered crystalline structure, and characterized their atomic-scale lattice distortions in terms of the local residual strains. Albeit the confounding chemical/geometric complexities, we are able to show that the average attributes of such an atomic-scale distorted lattice, such as the lattice constant and the overall magnitude of the distortion induced residual strains, can be predicted very well by a simple physical model taking into account the efficient packing of different sized atoms interacting in an effective elastic medium. The findings of our current research unveils the details of locally distorted atomic packing in chemically disordered complex alloys, which sheds quantitative insights into the unusual strengthening mechanism as recently discovered in high entropy alloys.

The most critical issues in microforming technologies are tailoring the desirable product quality and ensuring the high productivity from application perspective. This is also the case for fabrication of cylindrical micro-pin and flanged micropart with nonuniform thickness. To realize continuous micromanufacturing of the hollow flanged micropart with variable thickness, an efficient progressive microforming method is proposed by using an integrated hole flanging-ironing process. In this process, size effect and its affected deformation behavior and forming quality of the micropart are still not well known and knowing of them well is crucial in forming of the accurate shape and geometry of the microparts, tailoring the needed product properties and assuring the required qualities. This study thus aims at addressing these issues in terms of deformation load, forming kinematics, dimensional accuracy, defect formation and microstructural evolution based on an unequal-thickness flanged micropart produced by the developed progressive microforming system in which shearing, hole flanging-ironing and blanking operations are realized progressively. The experimental results reveal that the length of the flanged micropart is reduced with the increasing grain size, while both the tapering angle and its scatter present an opposite tendency, which could be explained by the coupled model of free surface roughening and open-closed lubricant pockets. Furthermore, the dimensional accuracy, surface appearance and the defects including curved profile, singularity, wrinkling and irregularity are closely related to the initial material microstructure. Through realization and examination of the developed progressive microforming system and the finished microparts, the progressive hole flanging-ironing process is proven to be promising and efficient for continuous micromanufacturing of micro-scaled hollow geometries with higher flange and variable thickness.

Silicene nanomesh (SNM), a silicene sheet with periodically arranged nanoholes, has gained increasing interest due to its unique geometry and novel properties. In this paper, we have conducted molecular dynamics simulations to study the phonon transport properties of SNMs. The results demonstrate that the thermal conductivity of SNM, which is shown to be much lower than that of silicene, is little affected by temperature but can be effectively tuned by varying the porosity. To elucidate the underlying mechanisms for decreased thermal conductivity, we have investigated both coherent and incoherent phonon transport in SNMs. It is found that the phonon backscattering at the nanopore edges leads to extra thermal resistances. Additionally, the introduction of nanopores induces phonon localization and consequently hinders phonon transport in SNMs. The phonons of SNM exhibit coherent resonant behavior, which is believed to reduce the phonon group velocities and thus leads to a further reduction in thermal conductivity of SNMs. Our findings could be useful in the design of thermal properties of silicene for applications in thermoelectrics, thermal insulation and thermal protection.

Graphene-based materials exhibit intriguing phononic and thermal properties. In this paper, we have investigated the heat conductance in graphene sheets under shear-strain-induced wrinkling deformation, using equilibrium molecular dynamics simulations. A significant orientation dependence of the thermal conductivity of graphene wrinkles (GWs) is observed. The directional dependence of the thermal conductivity of GWs stems from the anisotropy of phonon group velocities as revealed by the G-band broadening of the phonon density of states (DOS), the anisotropy of thermal resistance as evidenced by the G-band peak mismatch of the phonon DOS, and the anisotropy of phonon relaxation times as a direct result of the double-exponential-fitting of the heat current autocorrelation function. By analyzing the relative contributions of different lattice vibrations to the heat flux, we have shown that the contributions of different lattice vibrations to the heat flux of GWs are sensitive to the heat flux direction, which further indicates the orientation-dependent thermal conductivity of GWs. Moreover, we have found that, in the strain range of 0-0.1, the anisotropy ratio of GWs increases monotonously with increasing shear strain. This is induced by the change in the number of wrinkles, which is more influential in the direction perpendicular to the wrinkle texture. The findings elucidated here emphasize the utility of wrinkle engineering for manipulation of nanoscale heat transport, which offers opportunities for the development of thermal channeling devices.

The kinetics of sigma phase precipitation at the temperature range of 750–950 °C in a rapidly solidified 15Cr-2Ni-2Al-11Mn resource-saving duplex stainless steel was investigated. After fitting the experimental results with the Avrami equation, the TTT diagram of sigma phase was established. It is found that the precipitation rate of sigma phase maximizes at about 850 °C and that the precipitation hardening effect sharply peaks at about 1.5 vol% sigma phase content, which is obtained by aging at 850 °C for 180 min. With the further increase of sigma phase content from 1.5 vol%, the strength reduces and the ductility increases again.

Numerous studies confirm that three dimensional porous Cu–Sn (3DP Cu–Sn) anode possesses good application prospect in light of its desirable electrochemical performance on lithium ion half cells, but there are a few related systematic researches on lithium ion full cells until now, which is indispensable before its commercialization. Herein, the effects of galvanostatic charge-discharge voltage range on the cycling stability of 3DP Cu–Sn anode for lithium ion full cells are investigated systematically. The results show that the suitable charge-discharge voltage range plays a key role in improving the reversible capacity and cycling stability of the 3DP Cu–Sn||LiCoO2 full cell, which is closely related to maintaining the electrode structure stable by controlling the amount of Li+ extracted and inserted. Especially, in the voltage range of 1.2–3.9 ​V, the full cell exhibits remarkably improved electrochemical properties with the high initial reversible capacity of 2.71 ​mAh cm−2 and 71.95% capacity retention upon 80 cycles. We believe that this work can provide a significant reference for the practical application of porous Sn-based anodes.

Nanoclay has been a popular kind of nanofiller for polymer-based nanocomposites in industries since adding a small amount of it can effectively enhance the mechanical properties of polymer. In the present study, a suitable sonication time was first found for manufacturing nanoclay/epoxy adhesive. Then, the lap joint shear strengths of nanoclay/epoxy adhesives with different nanoclay content (0, 1, 3, 5 wt%) conditioned at both room temperature and cryogenic temperature environment were investigated. The main failure mechanism of all samples was interfacial failure between the first layer of glass fiber and adhesive due to peeling. Results showed that 1 wt% was the optimal nanoclay concentration for cryogenic temperature. Scanning electron microcopy was used to examine the fracture surfaces of samples. Good exfoliation and dispersion were found in samples containing 1 wt% of nanoclay. Adding nanoclay into epoxy did not greatly affect the lap joint shear strength at room temperature but significantly influence the strength at cryogenic temperature. This was due to a clamping force induced on nanoclay by negative thermal expansion during conditioning from room temperature to cryogenic temperature. With good exfoliation and dispersion, the clamping force can be evenly distributed. Hence, 1 wt% nanoclay/epoxy adhesive is suitable for bonding composite lap joints, which will be servicing at low temperature environment.

A numerical fiber pullout model tailored for carbon nanotube (CNT) reinforced polymer composites is developed based on some classical models, to evaluate the effect of low temperature environment and other parameters to the stress distribution and stress transfer efficiency in CNT/polymer composites. It is assumed that there are no bonding between CNTs and polymer so only frictional slip occurs in the interface. Results show that the required axial stress to pull out a straight CNT at cryogenic temperature is more than 6 times greater than that required at room temperature. Some other parameters, such as the length of CNT and the modulus of polymer, also influence the stresses in the CNT/polymer model. The model is also applied to coiled carbon nanotubes (CCNTs) which are newly-developed carbon nanotubes with a helical configuration. At cryogenic temperature, a greater stress is required to pull out a CCNT than a straight CNT, especially in the case when the pitch angle of CCNT is less than 60°. Hence, the stress transfer in CCNT/polymer composites is better than that in straight CNT/polymer composites.

A constitutive model considering the composition of surface grain, grain boundary and grain interior and their contributions to the flow stress or strength of materials in micro-scale plastic deformation is developed and termed as a combined surface layer and grain boundary strengthening model in this research. To determine the composition of the three interior microstructural parts of materials, optical microscope and digital image processing technologies are employed. A series of micro-tensile experiments using the specimens with three different geometrical shapes and microstructural grain sizes are conducted for study of deformation and ductile fracture behaviors of material. The model is implemented in finite element analysis and validated via physical experiments. The relationship among fracture strain, grain size and stress triaxiality of the deforming material is thus established. It is found both fracture strain and stress triaxiality increase with the decrease of grain size, while the high stress triaxiality leads to small fracture strain for the given grain size. Through observation of the fractographs, it is revealed that the domination of shear fracture in the ‘cup-cone’ fracture increases with grain size. The research thus helps understand the ductile fracture in micro-scale deformation and facilitates deformation based working process determination and application.

In macro-scaled plastic deformation, ductile fracture behaviors have been extensively investigated in terms of formation mechanism, deformation mechanics, influencing factors and fracture criteria. In micro-scaled plastic deformation, however, the fracture behaviors of materials are greatly different from those in macro-scale due to the existence of size effects. To explore the simultaneous interaction of size effect and stress condition on material fracture behavior in meso/micro-scaled plastic deformation, the tensile and compression tests of pure copper with various geometrical sizes and microstructures were conducted. The experiment results show that microvoids exist in compressed samples due to localization of shear band instead of macro fracture. Furthermore, the FE simulation is conducted by using the size dependent surface layer model, which aims to study the interaction of size effect and stress condition on material fracture behavior in multi-scaled plastic deformation. It is found that the stress triaxiality (T) generally increases with the ratio of surface grains η in compression statement. Fracture strain and fracture energy with positive T are much smaller than that with negative T regardless of geometrical and grain sizes. This research provides an in-depth understanding of the influences of size effect and stress condition on ductile fracture behavior in micro-scaled plastic deformation. Keywords: Size effect, Stress condition, Ductile fracture, Micro-scaled plastic deformation

Martensitic transformation (MT) has extreme science merits and engineering significance. However, the underlying displacive atom collective movements for the transition from face-centered cubic structure (fcc-γ) austenite to body-centered tetragonal structure (bct-α) martensite has not been uncovered due to the lack of directly experimental evidence. Here, we examined the Plastic Deformation-Induced Martensitic Transformation (PDIMT) from fcc-γ to bct-α in AISI 304 stainless steel by High-resolution Transmission Electron Microscopy (HRTEM). The HRTEM observations exhibit a novel polymorphic fcc-γ → hcp-e → bct-α PDIMT mechanism, which is further confirmed by the Molecular Dynamics (MD) simulations. The transition from fcc-γ to hcp - e is accomplished by gliding Shockley partial dislocations on every second (111)γ planes. The transition from hcp-e to bct-α is executed by gliding half-Shockley partial dislocation dipoles on every second (0001)e planes and the gliding is simultaneously accompanied by atom shuffling. The dipole shear is conducted in a sandwich manner, meaning that a half-Shockley partial dislocation glides on one side of a (0001)e plane and its partner of the dipole glides on the other side of the same (0001)e plane. The novel findings will have great impact on the microstructural control in metals and alloys by PDIMT and stimulate innovative ideas to understand other solid phase transition mechanisms.

The room-temperature duplex structure of duplex stainless steel is always metastable, which suggests that non-equilibrium phase transformation can be further exploited for producing duplex stainless steel having the same chemical compositions and phase constitution but different microstructures. This work uses rapid solidification obtained duplex stainless steel to expand heat-treatment temperature range for achieving 50/50 duplex structure. Research shows an equilibrium state for the phase constitution of duplex stainless steel after sufficiently long time annealing, and establishes the non-equilibrium kinetics diagram of ferrite-to-austenite transition in cold-rolled duplex stainless steel. It is then shown that the duplex stainless steel with about 50% austenite phase can be prepared using different non-equilibrium thermal process, of which the yield strength and elongation vary in the ranges of 306–499 MPa and 20–33%, respectively. The sample, which exhibits the best combination of yield strength (371 MPa) and elongation (33%), is attributed to the bimodal distribution of austenite grain size.

It was previously reported that the strength of metallic glasses (MGs) would scale inversely with the size of a sample or a deformation field, commonly known as “smaller-being-stronger”. However, based on the extensive spherical nanoindentation experiments conducted across a variety of MGs, we demonstrate that such strength-size scaling breaks down at a critical indenter tip radius, which is caused by the transition of the yielding mechanism from bulk- to surface-controlled shear band initiation. Our experimental findings also provide an explanation for the unusual strength scattering observed in the micro-compression of MGs.

Extensive efforts have been devoted in both the engineering and scientific domains to seek new designs and processing techniques capable of making stronger and tougher materials. One such method for enhancing such damage-tolerance in metallic alloys is a surface nano-crystallization technology that involves the use of hundreds of small hard balls which are vibrated using high-power ultrasound so that they impact onto the surface of a material at high speed (termed Surface Mechanical Attrition Treatment or SMAT). However, few studies have been devoted to the precise underlying mechanical mechanisms associated with this technology and the effect of processing parameters. As SMAT is dynamic plastic deformation process, here we use random impact deformation as a means to investigate the relationship between impact deformation and the parameters involved in the processing, specifically ball size, impact velocity, ball density and kinetic energy. Using analytical and numerical solutions, we examine the size of the indents and the depths of the associated plastic zones induced by random impacts, with results verified by experiment in austenitic stainless steels. In addition, global random impact and local impact frequency models are developed to analyze the statistical characteristics of random impact coverage, together with a description of the effect of random multiple impacts, which are more reflective of SMAT. We believe that these models will serve as a necessary foundation for further, and more energy-efficient, development of such surface nano-crystalline processing technologies for the strengthening of metallic materials.

Most metals naturally corrode in an engineering environment and form corrosion products. The corrosion products can be either soluble or insoluble in the aqueous solution. The insoluble corrosion products (ICP) could have profound effects on the corrosion kinetics of the concerned metal. In this study, a multi-phase-field formulation is proposed to investigate the effects of ICP formation on pitting corrosion kinetics. The Gibbs free energy of the metal-electrolyte-insoluble corrosion product system consists of chemical, gradient, and electromigration free energy. The model is validated with experimental results and several representative cases are presented, including the effect of the porosity of ICP, under-deposit corrosion, corrosion of sensitized alloys, and microstructure-dependent pitting corrosion. It is observed that corrosion rate and pit morphology significantly depend on ICP and its porosity for the same applied potential.

In this report, a simple and effective low-temperature synthesis route has been proposed to smoothly achieve monodisperse tin nanoparticles upon monolithic 3D nanoporous copper (3D-NPC@MTNPs) from chemical dealloying of as-cast Al–45 at% Cu alloy sheets in HCl solution; they exhibit superior Li storage properties and ultralong cycle life as the anode for lithium ion batteries (LIBs). The results show that the 3D-NPC@MTNPs composite can be fabricated on a large scale by electroless plating of Sn on a uniform NPC matrix with a pore size of ca. 200 nm in an acidic plating bath below room temperature. Compared to two dimensional copper foil supported tin thin films (2D-CF@TTFs), the 3D-NPC@MTNPs electrode displays a markedly higher first reversible capacity of 0.485 mA h cm−2 as well as superior cycling stability with 52.4% capacity retention and over 96.7% coulombic efficiency after 500 cycles. This can be largely ascribed to the synergistic effect between the favorable monodispersity of Sn nanoparticles with ultrafine particle size and single crystal nature and the unique 3D nanoporous electrode architecture with a large specific surface area and a good mass transfer channel, which facilitates the accommodation of mechanical strain, improvement of structural stability, enhancement of bonding force, and acceleration of mass transfer, which are indicative of a quite promising candidate as a high-performance anode for LIBs.

Developing efficient electrodes with superior rate performance and superb cyclability are highly desired for meeting urgent demand of high-energy and large-rate lithium ion batteries (LIBs). Electrochemical performance of popular transition metal oxide electrodes is severely restricted by its inferior structure stability and low conductivity, leading to rapid capacity fade at high current density or deep cycling. Herein, a unique 3D core-bishell (3D-CBS) nanoporous electrode with configuration of Cu (NPC) core and bi-layered conformal Cu2O@PANI shells was dedicatedly designed and built by a novel and cost-effective approach combining chemical dealloying with controlled electro-polymerization. The 3D-CBS nanoporous electrodes deliver a large reversible capacity of 349 mAh g−1 at 6000 mA g−1 after 11500 ultralong-cycles with 76% capacity retention, corresponding to only 0.002% capacity fade per cycle. The superb cyclability is related to the unique 3D-CBS electrode design and in-situ formation of Cu2O with exposed most Cu+ (Cu+/O2− = 4/1) and low-energy (111) crystal plane (0.046 eV/A2) on NPC matrix, as confirmed by physicochemical characterization and DFT calculation. Impressively, the 3D-CBS electrode displays superior rate capability with negligible capacity fade after 5 multistep-rate periods from 2 up to 20 A g−1 and back again to 2 A g−1 repeatedly (over 400 cycles), which is ascribed to the conformal coating of PANI as protective nanolayers with good conductivity on Cu2O, achieving ultrafast Li+ diffusivity (DLi = 2.42 × 10−10 cm2 s−1) and significantly improved electron conductivity (82000 S m−1). We believe that this work provides novel insights for design and synthesis of ultrahigh-rate and ultralong-life nanostructured anodes toward advanced LIBs.

Chemical dealloying beckons researchers both for scientific interest in corrosion failure of metallic materials and for the fabrication of nanoporous materials that have versatile applications due to their ultra-high surface area. Empirically, nanoporous structure evolves by the corrosion of less noble elements coupled with the rearrangement of more noble elements in the alloys. However, how topologically complex porous structures form and how environmental and material factors affect the dealloying kinetics are still unknown. This work develops a multi-phase-field model to demonstrate that a nucleation-growth mechanism can explain the formation of nanoporous structures under chemical attack. The evolution of nanoporous patterns from a binary alloy is examined as a function of the chemical content of the electrolyte, precursor alloy composition, dimensionality, and bulk and surface diffusion coefficients, which is validated with experimental observations. Two-phase composite dealloying and the effect of defect pre-existed in the precursor are also presented. The comprehensive model developed in this study provides a powerful tool to tailor made nanoporous metallic structures under chemical dealloying.

In this paper, novel freestanding 3D hierarchical porous SnOx-decorated Ni3Sn2 (3D-HP SnOx@Ni3Sn2) composites are synthesized facilely by two-step chemical dealloying of designed as-cast Sn-45 at.% Ni alloy in different corrosive solutions. The results show that the 3D-HP SnOx@Ni3Sn2 composites have a typical bimodal pore size distribution composed of a micron-sized ligament-channel structure with highly nanoporous channel walls built by ultrafine SnOx (x = 1, 2) nanoparticles (3–6 nm). The unique 3D-HP composites as a binder-free integrated anode for lithium ion batteries (LIBs) display a significantly improved Li storage performance with first reversible capacity of 2.68 mAh cm−2 and good cycling stability with 85.1% capacity retention and over 98.4% coulombic efficiency after 100 cycles (just 0.004 mAh cm2 per cycle for capacity fading). This can be mainly ascribed to the synergistic effect between chemically inert 3D microporous Ni3Sn2 substrate with robust mechanical stress buffer and good transfer mass channels and in-situ growth of nanoporous SnOx with large specific surface areas and high electrochemical active sites. We believe that the present work can offer a promising anode candidate toward advanced LIBs.

The critical casting diameter (Dmax) quantitatively represents glass-forming ability (GFA) of bulk metallic glasses (BMGs). The present work constructed a dataset of two subsets, L-GFA subset of 376 BMGs with 1 mm ≤ Dmax ≥ 5 mm. The sequential backward selector and exhaustive feature selector are introduced to select key features. The trained XGBoost classifier with four selected features is able to successfully classify the L-GFA and G-GFA BMGs. Furthermore, the trained XGBoost regression model with another four selected features predicts the Dmax of G-GFA samples with a cross-validated correlation coefficient of 0.8012. The correlation between features and Dmax will provide the guidance in the design and discovery of novel BMGs.