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Abstract In this study, we utilized a quantitative atomistic analysis approach to investigate the impact of chemical ordering structures on the diffusion behavior of interstitials and vacancies within the CrCoNi medium entropy alloy (MEA), employing an advanced neural network interatomic potential (NNP). We discovered that the degree of chemical ordering, which can be precisely controlled through annealing at elevated temperatures, significantly influences both interstitial and vacancy diffusion. This phenomenon contributes to the notable sluggish diffusion characteristic of CrCoNi, largely attributable to the restriction of diffusion pathways in regions with lower degree of chemical ordering. We also emphasized the crucial role of operating temperature on diffusion, which should be remained well below the annealing temperature to preserve the sluggish diffusion effect. Our research sheds light on the interplay between chemical ordering and defect diffusion in MEAs, and it proposes effective strategies for tailoring the diffusivity of MEAs by altering their chemical ordering. These insights are instrumental in the development of next-generation materials, which are optimized for use in challenging environments, such as high-temperature and irradiation conditions.

Abstract Near infrared energy remains untapped toward the maneuvering of entire solar spectrum harvesting for fulfilling the nuts and bolts of solar hydrogen production. We report the use of Au@Cu7S4 yolk@shell nanocrystals as dual-plasmonic photocatalysts to achieve remarkable hydrogen production under visible and near infrared illumination. Ultrafast spectroscopic data reveal the prevalence of long-lived charge separation states for Au@Cu7S4 under both visible and near infrared excitation. Combined with the advantageous features of yolk@shell nanostructures, Au@Cu7S4 achieves a peak quantum yield of 9.4% at 500 nm and a record-breaking quantum yield of 7.3% at 2200 nm for hydrogen production in the absence of additional co-catalysts. The design of a sustainable visible- and near infrared-responsive photocatalytic system is expected to inspire further widespread applications in solar fuel generation. In this work, the feasibility of exploiting the localized surface plasmon resonance property of self-doped, nonstoichiometric semiconductor nanocrystals for the realization of wide-spectrum-driven photocatalysis is highlighted.

Some solute atoms induce strengthening and embrittlement in body-centered cubic refractory metals. Especially, interstitial oxygen produces remarkable strengthening effects in Nb, wherein the yield stress of oxygen-doped Nb alloys is more than twice that of pure Nb. Conventional mechanisms cannot explain this oxygen-induced dramatic strengthening because the interaction between dislocations and oxygen atoms is not so significant. In a previous study, we found that the formation of vacancy–oxygen pairs enhances the attractive interaction with a screw dislocation and increases the energy barrier for dislocation motion associated with cross-kink nucleation in Nb–O alloys. However, the strengthening effect could not be described by the pinning model for dislocation motion. Herein, we focused on the atomic-level analysis of the fundamental process related to the dislocation motion around a vacancy, an oxygen atom, and a vacancy–oxygen pair. First-principles calculations revealed that the vacancy–oxygen pairs increase the energy barrier with respect to the dislocation motion more substantially than vacancies and oxygen interstitials owing to a unique oxygen-induced mechanism; an octahedral–tetrahedral shuffling process of oxygen is necessary for dislocation passing through vacancy–oxygen obstacles. Such event almost never happens in the real metallic materials. Instead, cross-kink nucleation occurs frequently to overcome the widely distributed vacancy–oxygen obstacles, which contributes to the dramatic strengthening.

Abstract The hydrogen evolution reaction (HER) and Zn dendrites growth are two entangled detrimental effects hindering the application of aqueous Zn batteries. The alloying strategy is studied to be a convenient avenue to stabilize Zn anodes, but there still lacks global understanding when selecting reliable alloy elements. Herein, it is proposed to evaluate the Zn alloying elements in a holistic way by considering their effects on HER, zincphilicity, price, and environmental‐friendliness. Screening selection sequence is established through the theoretical evaluation of 17 common alloying elements according to their effects on hydrogen evolution and Zn nucleation thermodynamics. Two alloy electrodes with opposite predicted effects are prepared for experimental demonstration, i.e., HER‐inhibiting Bi and HER‐exacerbating Ni. Impressively, the optimum ZnBi alloy anode exhibits one order of magnitude lower hydrogen evolution rate than that of the pure Zn, leading to an ultra‐long plating/stripping cycling life for more than 11 000 cycles at a high current density of 20 mA cm−2 and 81% capacity retention for 170 cycles in a Zn‐V2O5 pouch cell. The study not only proposes a holistic alloy selection principle for Zn anode but also identifies a practically effective alloy element.

Magnesium (Mg) & its alloys are favourable for orthopaedic & cardiovascular medical device fabrication applications, but holds a natural ability to degrade biologically when put with aqueous solution of the substances and/or water-saturated tissue in the context of a living organism. Mg alloys nature to corrode inside the living organism body is mainly attributed to the excessive rates of corrosion of Mg. Poor corrosion resistance possessed by Mg decreases the mechanical properties of the implants, and adds toxic effects on the bone metabolism. A potential method for increasing Mg alloy resistance to corrosion without changing its properties is by the protective polymeric deposit coatings. Moreover, to impart better mechanical and biocompatible aspects to Mg based materials biopolymers have been used as a composite constituent. This review is based on such composite materials constituting Mg and biopolymers. Their resulting favourable mechanical and osteopromotive properties in conjunction with biocompatibility may help the clinicians to fix the existing orthopaedic related issues.

Conducting polymer nanocomposites (CPNC's) are promising materials for sensor devices possessing design pliability, good sensitivity, and low temperature operation. For producing conducting polymer nanocomposites with tunable morphology, the soft template procedure is one of the advantageous aspects as reported from in-depth literature. Since the diameter and aspect ratio of conducting-polymer nanomaterials have affected the charge-transport properties, hence, the fine tuning of their structures is important to enhance sensitivity. This review has focused on the CPNC's membranes, insulative-polymers with conductive-fillers based CPNC's (IPCFCPNC's) and conductive-fillers based polymer nanocomposites (CFPNC's) which have been incorporated in many prior literary sources including the usage of strain sensors in some sensing applications for detection pressure, gas humidity, etc. As the review sheds light on incorporating specific types of nanofillers, such as graphene or carbon nanotubes or conducting filling-agents, into the CPNC's membrane matrix and insulative-polymeric-matrices, it will be possible to improve their mechanical stability, enabling them to be used for high-performance sensing applications. In addition, the review has evident that by using advanced fabrication techniques, such as electrospinning, it is possible to create thin, flexible CPNC's membranes that exhibit high sensitivity and stability towards target analytes. Therefore, the feasibility of CPNC's, IPCFCPNC's, and CFPNC's in sensor applications has thoroughly been reviewed for the purpose to realize the novel flexible CPNC structures and their other aspects of applications that may cater to new horizons in high-end smart flexible sensing applications. Additionally, the advanced discovery is to combine conductivity measurement and rheology analysis using a new emerging class of CPNC's, IPCFCPNC's, and CFPNC's for remarkable electrical properties. It is highly appealing to find out more about novel CPNC's, IPCFCPNC's, and CFPNC's, and their role in sensor matrices, considering their unique properties. Based on conducting polymers (CPs), and insulative-polymers with conductive filling-agents that have been reported during the past forty years, the properties and performance of sensing matrices have been investigated by incorporating the diverse carbon-based nano-additives and other nano filling-agents. Furthermore, another area of interest is the use of CPCs, and insulative-polymers with conductive filling-agents for the development of bio-sensors. CPCs, and insulative-polymers with conductive filling-agents can be functionalized with biological molecules such as enzymes, antibodies, and nucleic acids, to create highly sensitive sensors for the detection of various biological markers, including glucose, lactate, and pH. Along with myriads of illustrations in accordance with the CPs and their composites with nanoparticles, carbon materials, or conductive filling-agents with insulative-polymeric-matrices etc., their salient characteristics have been enumerated in this comprehensive review. Additionally, CPNC's, IPCFCPNC's, and CFPNC's-sensing devices will have to improve their analytical performance for a widespread spectrum of multifaceted sensing applications in future research trends.

Sluggish diffusion effect of high entropy alloy limits its diffusion bonding with other components in practical applications. In this paper, the surface mechanical attrition treatment (SMAT) strategy for performing diffusion bonding joints of high entropy alloy (HEA) at a relative lower temperature is proposed. The EDS results demonstrate that the diffusion distance of Fe atoms increases significantly after SMAT since more gain boundaries are formed after SMAT. Furthermore, with this method the HEA/stainless steel joint can achieve a useable strength of 320 MPa at relative lower temperature of 850 °C (∼0.63 Tm, Temperature of melting). Molecular dynamics simulations show that the apparent diffusivity of Fe in the polycrystalline model is significantly higher than in the single-crystalline model because of fast diffusion at grain boundaries, i.e., the grain boundaries are fast diffusion channels. More detailed microstructure analysis indicates that although the density of dislocations increases after SMAT, its elemental diffusion ability is much weaker compared with grain boundaries. This study provides a feasible avenue for the application of diffusion bonding in HEAs, which could greatly broaden the applications fields of HEAs.

As the sample size goes down to the nanoscale, the surface-related mechanism plays an important role in the deformation of nanoscale crystals. Here, the authors report breakdown of the traditional Hall-Petch-like relation in nanoscale Ag attributed to diffusion-involved nucleation behaviors.

Using a recent linear scaling method that fully accounts for anharmonic thermal vibrations, we calculated the activation free energy for $ \{10\bar {1}2\} $ twin boundary migration in magnesium up to 450 K, under both resolved shear stresses and non-glide stresses resulting from c-axis tension. Comparing to direct molecular dynamics data, we show that the harmonic transition state theory unexpectedly overestimates the activation entropy above temperatures as low as 100 K, leading to underestimates of the nucleation time by many orders of magnitude. Whilst a specific interface is studied, anharmonic and non-glide effects are expected to be generally significant in thermally activated interface migration.

Abstract Solid-state precipitation is a key heat-treatment strategy for strengthening engineering alloys. Therefore, predicting the precipitation process of localized solute-rich clusters, such as Guinier–Preston (GP) zones, is necessary. We quantitatively evaluated the critical nucleus size and nucleation barrier of GP zones in Al–Cu alloys, illustrating the precipitation preferences of single-layer (GP1) and double-layer (GP2) GP zones. Based on classical nucleation theory using an effective multi-body potential for dilute Al–Cu systems, our model predicted GP1 and GP2 precipitation sequences at various temperatures and Cu concentrations in a manner consistent with experimental observations. The crossover between formation enthalpy curves of GP1 and GP2 with increasing cluster size determines the critical conditions under which GP2 zones can nucleate without prior formation of GP1 zones. This relationship reflects competing interactions within and between clusters. The results illustrate the underlying mechanisms of competing nucleation between zones, and provide guidance for tailoring aging conditions to achieve desired mechanical properties for specific applications.

Although power laws are observed during nanoindentation and the power-law exponents are estimated to be approximately 1.5-1.6 for face-centered cubic metals, the origin of the exponent remains unclear. In this paper, we show the power-law statistics in pop-in magnitudes and unveil the nature of the exponent.

Inspired by the traditional Czochralski method of growing single crystal from liquid, the authors demonstrated that at nanoscale, metallic nanowires including Al, Ag, Cu and Sn can be controllably grown from the surface of a hot solid, by simply drawing a cold tip back after touching.

Segregation of rare earth alloying elements are known to segregate to grain boundaries in Mg and suppress grain boundary sliding via strong chemical bonds. Segregation of Mn, however, has recently been found to enhance grain boundary sliding in Mg, thereby boosting its ductility. Taking the Mg (2¯114) twin boundary as an example, we performed a first-principles comparative study on the segregation and chemical bonding of Y, Zn, and Mn at this boundary. We found that both Y-4d and Mn-3d states hybridized with the Mg-3sp states, while Zn–Mg bonding was characterized by charge transfer only. Strong spin-polarization of Mn pushed the up-spin 3d states down, leading to less anisotropic Mn–Mg bonds with more delocalized charge distribution at the twin boundary, and thus promotes grain boundary plasticity, e.g., grain boundary sliding.

Structural rejuvenation in metallic glasses by a thermal process (i.e. through recovery annealing) was investigated experimentally and theoretically for various alloy compositions. An increase in the potential energy, a decrease in the density, and a change in the local structure as well as mechanical softening were observed after thermal rejuvenation. Two parameters, one related to the annealing temperature, Ta/Tg, and the other related to the cooling rate during the recovery annealing process, Vc/Vi, were proposed to evaluate the rejuvenation phenomena. A rejuvenation map was constructed using these two parameters. Since the thermal history of metallic glasses is reset above 1.2Tg, accompanied by a change in the local structure, it is essential that the condition of Ta/Tg ≥ 1.2 is satisfied during annealing. The glassy structure transforms into a more disordered state with the decomposition of icosahedral short-range order within this temperature range. Therefore, a new glassy structure (rejuvenation) depending on the subsequent quenching rate is generated. Partial rejuvenation also occurs in a Zr55Al10Ni5Cu30 bulk metallic glass when annealing is performed at a low temperature (Ta/Tg ~ 1.07) followed by rapid cooling. This behavior probably originates from disordering in the weakly bonded (loosely packed) region. This study provides a novel approach to improving the mechanical properties of metallic glasses by controlling their glassy structure.

Abstract Theoretical prediction of glass forming ability (GFA) of metallic alloys is a key process in exploring metallic alloy compositions with excellent GFA and thus with the ability to form a large-sized bulk metallic glass. Molecular dynamics (MD) simulation is a promising tool to achieve a theoretical prediction. However, direct MD prediction continues to be challenging due to the time-scale limitation of MD. With respect to practical bulk metallic glass alloys, the time necessary for quenching at a typical cooling rate is five or more orders of magnitude higher than that at the MD time-scale. To overcome the time-scale issue, this study proposes a combined method of classical nucleation theory and MD simulations. The method actually allows to depict the time-temperature-transformation (TTT) diagram of the bulk metallic glass alloys. The TTT directly provides a prediction of the critical cooling rate and GFA. Although the method assumes conventional classical nucleation theory, all the material parameters appearing in the theory were determined by MD simulations using realistic interatomic potentials. The method is used to compute the TTT diagrams and critical cooling rates of two Cu-Zr alloy compositions (Cu50Zr50 and Cu20Zr80). The results indicate that the proposed method reasonably predicts the critical cooling rate based on the computed TTT.

Abstract The physical origins of the mechanical properties of Fe-rich Si alloys are investigated by combining electronic structure calculations with statistical mechanics means such as the cluster variation method, molecular dynamics simulation, etc, applied to homogeneous and heterogeneous systems. Firstly, we examined the elastic properties based on electronic structure calculations in a homogeneous system and attributed the physical origin of the loss of ductility with increasing Si content to the combined effects of magneto-volume and D03 ordering. As a typical example of a heterogeneity forming a microstructure, we focus on grain boundaries, and segregation behavior of Si atoms is studied through high-precision electronic structure calculations. Two kinds of segregation sites are identified: looser and tighter sites. Depending on the site, different segregation mechanisms are revealed. Finally, the dislocation behavior in the Fe–Si alloy is investigated mainly by molecular dynamics simulations combined with electronic structure calculations. The solid-solution hardening and softening are interpreted in terms of two kinds of energy barriers for kink nucleation and migration on a screw dislocation line. Furthermore, the clue to the peculiar work hardening behavior is discussed based on kinetic Monte Carlo simulations by focusing on the preferential selection of slip planes triggered by kink nucleation.

Amorphous materials of homogeneous structures usually suffer from nonuniform deformation under shear, which can develop into shear localization and eventually destructive shear band. One approach to tackle this issue is to introduce an inhomogeneous structure containing more than one phase, which can reduce the local nonuniform shear deformation and hinder its percolation throughout the system. Using thermostated molecular dynamics (MD) simulations, we compare the deformation behavior between a homogeneous amorphous mixture of bidisperse disc particles, interacting via an n − 6 Lennard-Jones potential of tunable softness, with an inhomogeneous one containing an evenly-distributed ordered phase. We change the population ratio of large to small particles to create a homogeneous or an inhomogeneous mixture, where the softness of a chosen phase can be manually adjusted by specifying n of the interparticle potential. Results of applying extensive quasistatic shear on the prepared mixtures reveal that the inhomogeneous amorphous mixture containing a soft ordered phase overall deforms more uniformly than the homogeneous one, which indicates that both the structure inhomogeneity and the inter-phase softness variance play important roles in enhancing the uniformity of the plastic deformation under shear.

Dislocation pipe diffusion seems to be a well-established phenomenon. Here we demonstrate an unexpected effect, that the migration of interstitials such as carbon in iron may be accelerated not in the dislocation line direction ξ, but in a conjugate diffusion direction. This accelerated random walk arises from a simple crystallographic channeling effect. c is a function of the Burgers vector b, but not ξ, thus a dislocation loop possesses the same everywhere. Using molecular dynamics and accelerated dynamics simulations, we further show that such dislocation-core-coupled carbon diffusion in iron has temperature-dependent activation enthalpy like a fragile glass. The 71° mixed dislocation is the only case in which we see straightforward pipe diffusion that does not depend on dislocation mobility.