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Co-based catalysts have gained significant attention in recent years due to their excellent ability to activate C-H bonds and high selectivity towards olefins, despite being a non-noble and environmentally unfriendly metal. However, further improvements are necessary for practical utilization, particularly in terms of activity and anti-carbon deposition capacity. In this study, we synthesized Al2O3 nanorods with abundant pentacoordinated Al3+ (Al3+penta) sites. The supported Co on the Al2O3 nanorod (Co/Al2O3-NR) exhibited higher selectivity (>96% propylene selectivity) and stability (deactivation rate 0.15 h-1), compared to Co supported on an Al2O3 nanosheet with fewer pentacoordinated Al3+ sites. Various characterizations confirmed that Co(II) mainly exists as CoAl2O4 rather than Co3O4 in the form of Co/Al2O3-NR, which inhibits the reduction of Co(II) to Co0 and improves catalyst stability accordingly.

The direct effects of carbon fiber-reinforced polymer (CFRP) composites with a fastener in lightning environments are very complicated. Experimental models were designed to understand the influence of different factors on the damage modes. First, different specimen structures, including unidirectional and woven fabric, were studied. Second, the damage characteristics of the two cases where current injection occurred in the fastener part and the carbon fiber part were experimentally studied. Finally, the different grounding points were studied. The experimental results showed that the woven fabric structure can conduct current better, and the area of lightning damage is smaller than that of the unidirectional ply. The lightning experimental conditions had a significant influence on outgassing, delamination damage characteristics and the lightning phenomenon. A high-speed camera was used to observe the lightning action process. The mechanism of electrical and thermal conversion between fastener and CFRP composites was revealed by discussing the lightning strike process. The damage morphology and lightning phenomena caused by an instantaneous electric field distortion distribution was deduced. The current work provides a reference for effectively designing lightning protection strategies under different lightning strike conditions.

We demonstrate a strategy to stabilize nanoprecipitates in Al–Cu alloys, based on computational design that identifies synergistic solutes (Sc and Fe) that simultaneously segregate to the θ′-Al2Cu/Al interface and strongly bond to one another. Furthermore, Sc and Fe are predicted to each segregate into a separate atomic plane, forming a sandwiched structure reinforcing the interface. This interfacial architecture was realized through a simple heat treatment in a Sc–Fe–Si triple-microalloyed Al–Cu model alloy. Such a back-to-back layered interface, thermodynamically stable and kinetically robust, is found to suffocate nanoprecipitate coarsening at 300°C, enabling a dramatic reduction in creep rate. IMPACT STATEMENT The segregant architecture of synergistic solute at θ′-Al2Cu/Al interface was guided by computational calculations and artificially realized at atomic scale to achieve an ultra-high thermal stability of θ′-Al2Cu, leading to a high creep resistance at 300°C.

While carbon-fiber-reinforced polymers (CFRPs) are widely used in the aerospace industry, they are not able to disperse current from lightning strikes because their conductivity is relatively low compared to metallic materials. As such, the undispersed current can cause the vaporization or delamination of the composites, threatening aircraft safety. In this paper, finite element models of lightning damage to CFRPs were established using commercial finite element analysis software, Abaqus, with the user-defined subroutines USDFLD and HEAVEL. The influences of factors such as the structural geometry, laminate sequence, and intrinsic properties of CFRPs on the degree of damage to the composites are further discussed. The results showed that when a current from lightning is applied to the CFRP surface, it mainly disperses along the fiber direction in the outermost layer. As the length of the CFRP increases, the injected current has a longer residence time in the material due to the increased current exporting distance. Consequently, larger amounts of current accumulate on the surface, eventually leading to more severe damage to the CFRP. This damage can be alleviated by increasing the thickness of the CFRP, as the greater overall resistance makes the CFRP a better insulator against the imposed current. This study also found that the damaged area increased as the angle between the first two layers increased, whereas the depth of the damage decreased due to the current dispersion between the first two layers. The analysis of the electrical conductivity of the composite suggested that damage in the fiber direction will be markedly reduced if the conductivity in the vertical fiber direction increases approximately up to the conductivity of the fiber direction. Moreover, increasing the thermal conductivity along the fiber direction will accelerate the heat dissipation process after the lightning strike, but the influence of the improved thermal conductivity on the extent of the lightning damage is less significant than that of the electrical conductivity.

In order to quantify the fracture toughness and reveal the failure mechanism of crystalline/amorphous nanolaminates (C/ANLs), in-situ micro-cantilever bending tests were performed on Ag/Cu–Zr and Mo/Cu–Zr C/ANLs in a scanning electron microscope over a wide range of cantilever widths from several microns to the submicron scale. The results demonstrate that the fracture behavior was strongly influenced by sample size and constituent phases, respectively. The Ag/Cu–Zr micro-cantilevers failed in a ductile manner, with fracture toughnesses higher than the Mo/Cu–Zr samples that exhibited brittle failure. Both materials also displayed different cantilever width-dependences of fracture toughness. The Ag/Cu–Zr beams showed a fracture toughness that increases with the cantilever width, mainly due to a size-dependent constraining effect on the deformation of the crystalline phase. For the Mo/Cu–Zr beams, the fracture toughness decreased gradually to a low plateau as the cantilever width exceeded ∼1500 nm, which can be rationalized by a transition in stress condition. The underlying fracture mechanism of the Ag/Cu–Zr micro-cantilevers was identified as the interconnection of microcracks initiated in the amorphous Cu–Zr layers, compared to a catastrophically penetrating crack propagation in the Mo/Cu–Zr samples. The discrepancy in size-dependent fracture behavior between the two material systems is discussed in terms of plastic energy dissipation of ductile phases, crack tip blunting, crack bridging and the effect of strain gradient in the plastic zone on crack propagation.

Nanostructured crystalline Al/amorphous AlN multilayer films with a wide layer thickness (h) range from ∼10 nm up to ∼200 nm were prepared by using magnetron sputtering. Nanotwins and 9R phase were substantially observed in the Al layers, showing a strong thickness dependence. The 9R phase predominantly penetrated through the Al layer in the II regime of h ≤ ∼20 nm, while mainly terminated within the layer interior in the I regime of h > ∼20 nm. On the contrary, the coherent nanotwins were boosted when h > ∼20 nm and the percentage of twinned Al grains was greatly increased. The formation mechanisms of 9R phase and coherent nanotwins were discussed in terms of the interfacial chemistry/physics modulated by the amorphous AlN layers, which displayed gradient characteristics and hence was sensitive to the layer thickness. A significant thickness dependence of hardness was also evident that the hardness monotonically increased with reducing h in the I regime, while reached a peak value and hold almost unchanged in the II regime. The hardness in the II regime is about 1 GPa greater than the predictions from an interfacial barrier crossing model. This discrepancy is mainly contributed by the layer-penetrating 9R phase rather than the nanotwins. This study provides a new perspective on fabricating nanotwinned Al by utilizing heterophase interfaces.

The distribution and conduction path of lightning current inside carbon fiber-reinforced polymer (CFRP) composites subjected to lightning strikes are determined by their dynamic conductive characteristics. An experimental platform that generates lightning current impulses with variable parameters was established to obtain the equivalent conductivities of CFRPs with different laminated structures. The experimental results indicated that the through-thickness conductivity (10−3 S/mm) was much lower than the in-plane conductivity (100 S/mm). Then, the dynamic conduction model of CFRPs was analyzed based on the anisotropic nonlinear conductivities of CFRPs under lightning currents of 50–1000 A. The CFRP laminate could be regarded as a series circuit of resistance and inductance. The dynamic conductance of the CFRP laminate first increased and then decreased during the single lightning current strike process, which was closely related to the conductive properties of the interlaminar resin. The inductive properties of the CFRP material were manifested in the test results, which showed that the voltage reached the peak value prior to the current waveform and the equivalent conductivities of the CFRPs increased as the rate of increase decreased and the duration increased. In addition, the equivalent inductance of the carbon fiber network was found to be an important part of the inductive effect of CFRP laminates. This research is helpful for understanding the complicated relationships in the lightning current conducting process and can provide experimental and theoretical support for CFRP coupled electrical–thermal simulation studies of lightning direct effects.

To date, the predictive analysis of lightning-induced damage of carbon fiber reinforced polymer composites (CFRP) is challenging due to the complex multi-physical coupling effects. The current study aims to clarify the lightning-induced damage mechanism of CFRP and improve the lightning protection systems for aerospace applications. Herein, an artificial lightning strike experiment was designed to simulate the real-life conditions and investigate the influence of lightning strike on a quasi-isotropic CFRP sample. The lightning strike and corresponding degradation process were observed by using a high-speed camera and infrared thermal imaging. Moreover, lightning-induced damage was assessed by visual inspection and non-destructive testing. The damage behavior of CFRP composites was deduced by analyzing the lightning process and damage modes. The results reveal that the damage is caused by the electro-thermo-mechanical response due to lightning arc flow and Joule heating ablation due to the conductive nature of the CFRP composites. The current work provides an enhanced understanding of the failure mechanism under lightning strike and outlines instructional suggestions to refine the numerical model of lightning-induced damage of CFRP for further study.

The lightning damage depths and areas of carbon fiber reinforced polymer (CFRP) laminates subjected to multiple continuous sequential lightning current components with different timing combinations were experimentally evaluated. The experimental results indicated that the CFRP laminates suffered serious lightning damage, including fracture of the carbon fibers and layer delamination. After a multiple lightning strike composed of lightning components A, B and C, the surface temperature of the CFRP laminates, which was projected from the measured temperature with lower magnitude, can exceed 1600 °C. The damage area and depth were approximately 2790 mm2 and 1.28 mm in the “ABCD” test mode. The damage depth was found to be closely related to lightning components A, B and D, which are accompanied by the shockwave and the overpressure effect, the dielectric breakdown effect and the local thermal effect. The increases in the surface temperature and damage area after lightning strike were mainly affected by the lightning component C with substantial thermal effect. The application sequence and material properties are important factors for evaluating the damage effect of the newly added lightning component on samples that have suffered from multiple continuous lightning components. The influencing factors and analysis method for CFRP laminate lightning damage subjected to multiple continuous sequential lightning components may provide both experimental support and a theoretical basis for studying the mechanism of the lightning effect and the refinement and improvement of a lightning direct effect test method for CFRP laminates in the future.

Previous studies demonstrated that the He ion irradiation damage tolerance of nanostructured metallic multilayers (NMMs) was closely dependent on the layer thickness (h): smaller h led to lower irradiation hardening. Here in Mo/Zr NMMs, we uncovered that the h-dependent irradiation hardening and corresponding plastic deformation characteristics are also sensitive to the He+ irradiation fluences. At a low irradiation fluence of 1.0 × 1016 He+·cm−2, the irradiation hardening decreased monotonically with reducing h. While at a high irradiation fluence of 1.0 × 1017 He+·cm−2, a non-monotonic h-dependence was unexpectedly displayed with the minimum irradiation hardening at h of ∼25 nm. The irradiation fluence also affects the strain rate sensitivity (m) remarkably. Irradiation of 1.0 × 1016 He+·cm−2 induced a transition in SRS m from positive in the as-deposited Mo/Zr NMMs to negative SRS in their irradiated counterparts. This transition was rationalized in terms of dynamic strain aging that considered dislocation-bubble interactions. Irradiation of 1.0 × 1017 He+·cm−2, however, resulted in a non-monotonic h-dependence of m, with the bottom located at a turning point of h ∼50 nm. Coupling effect of the layer thickness and the applied fluence on irradiation hardening and plastic deformation characteristics was quantitatively elucidated by employing a strengthening model and a thermally activated model, respectively, where parameters of the characteristic microstructural features, i.e., the layer thickness and irradiation (He) defects, were both included.

The lightning test method with a single lightning component C was found to be inappropriate to simulate the lightning effect on optical-fiber overhead ground wires (OPGWs). This study establishes a multiple lightning current test system, including intermediate current component B and continuing current component C, to investigate the lightning test method for OPGWs. The lightning characteristics and damage performance of OPGWs with different test conditions under multiple sequential lightning currents were experimentally evaluated via visual inspection and infrared temperature measurement. The test results indicated that the lightning damage of OPGWs was not only related to the parameters of the applied lightning current but also the experimental method. The lightning erosion degree and surface temperature of OPGWs increased as the transfer charge of current component C increased. When the transfer charge was approximately 200 °C, the surface temperature exceeded 3600 °C. Moreover, as the discharge gap increased from 5 cm to 6 cm, the temperature decreased, and the lightning damage degree, particularly the number of broken strands, decreased accordingly. The research on the lightning test method in this paper may provide experimental support and a theoretical basis for a proper evaluation of the lightning protection performance OPGWs and the study of the lightning effect mechanism.

Grain boundary (GB) engineering via alloying opens a pathway to design the interfaces in alloys for tuning their mechanical properties, thus it is quite critical to determine the optimum addition of alloying element. Here, we prepared immiscible Cu-Cr alloyed thin films by non-equilibrium magnetron sputtering deposition to study Cr alloying effects on the microstructure and mechanical properties of Cu thin films. It is found that Cr doping can notably refine the grains and promote the formation of fully nanotwinned columnar grains at low Cr volume concentrations (≤∼3.7 at.%) associated with the average GB Cr concentrations ≤ ∼15 at.%, beyond which the formation of nanotwins is significantly suppressed. The role of Cr atoms/clusters played in the twinning process is rationalized in terms of dislocation rebound-promotion mechanism. Importantly, a maximum hardness is discovered at the optimum Cr addition of ∼2.0 at.%. The Cr concentration-dependent hardness of Cu-Cr alloyed films was quantified by a combined strengthening model. The achievement of the maximum hardness was related to the greatest GB solute segregation-induced strength contribution. It is further uncovered that the Cu-Cr system exhibits strain rate sensitivity (SRS, m) monotonically reduced with increasing the Cr concentration, ranging from a positive m of 0.0314 (for pure Cu) to a negative m of −0.0245, which is attributed to a competition between the dislocation-boundary interactions (increasing m) and the dislocation-solute atoms interactions (decreasing m). These findings provide valuable insights into tuning the composition of alloyed thin films to achieve optimized mechanical performance.

Here we report the effects of Zr addition (0.1–0.3 at.%) on the multi-scale second-phase particles and fracture behavior for Mg-3Gd-1Zn (at.%) alloys. Microstructural features of the alloys in the as-cast, solutionized, and aged conditions have been investigated in detail. The results have revealed that the cast alloys are mainly composed of α-Mg matrix, eutectic phase (Mg, Zn)3Gd, 14H long period stacking ordered (LPSO) structure and cuboid shaped GdH2 phase. After solution heat treatment, the eutectic phase (Mg, Zn)3Gd has transformed to X phase with 14H-LPSO structure, which has different distributions and morphologies due to different Zr additions. When the Zr addition is 0.3 at.%, a large amount of microscale Mg(Gd, Zn, Zr) particles appear along the grain boundaries. After aging heat treatment, Mg-3Gd-1Zn alloy with basal precipitates γ '' exhibits poor age-strengthening response. In contrast, Zr addition to the Mg-3Gd-1Zn alloy gave rise to a strong age-strengthening response. The strength improved significantly due to dense distribution of nanoscale prismatic plate β ' and β 1 precipitates, which are not observed in the Zr-free alloys. One key finding of this study is that Zr contributes to formation of the prismatic precipitates, and their amount increase with increase of Zr addition. The mechanical damage for these alloys is a sequence of microscale GdH2 or Mg (Gd, Zn, Zr) particles cracking, followed by fracture of the surrounding particles, and finally the growth/coalescence of micron-voids in the α-Mg matrix. The fracture of microscale particles was quantitatively analyzed by a Weibull model.

This study aimed to reveal the lightning-induced conduction characteristics and improve the lightning damage simulation of carbon fiber-reinforced polymer (CFRP) composites. The real-time conductivity of CFRPs under lightning impulses was investigated. A potential barrier model of “fiber-resin-fiber” units was established based on the electron hopping and tunneling effect to clarify the nonlinear conduction mechanism. An impulse equivalent circuit model of CFRPs was constructed and experimentally verified. The effective resistance was proposed and incorporated into the coupled thermoelectrical damage analysis of CFRPs under lightning component A. The simulated damage based on different conductivity models was compared with the experimental results, indicating that the adoption of effective resistance can advance the simulation study of lightning-induced damage in actual lightning environments. This adoption can decrease the maximum deviation in simulated in-plane damage from −42.8% to −8.86% and decrease the deviation in the predicted through-thickness damage from 2 to 3 layers to within 1 layer.

Lightning strike damage has become a primary issue limiting the extensive application of carbon fibre-reinforced polymer (CFRP) composites in the aerospace field. A detailed understanding of the physical interactions involved in the lightning strike process is still lacking, especially regarding the lightning-induced mechanical effects that potentially contribute to fracture and ply delamination in CFRP structures. This paper presents research on shock wave pressure induced by impulse currents on CFRP laminates. A novel method that exploits a polyvinylidene fluoride (PVDF) piezoelectric sensor was developed to directly measure the pressure induced by arc channel expansion. The influences of discharge polarity, strike distance and surface condition on the shock wave pressure were investigated. The results showed that the shock wave pressure produced by negative discharge was greater than that produced by positive discharge, the difference between which was reasonably explained based on the polarity effect concept. Increases in current amplitude and strike distance both contributed to larger measured pressures. A woven copper mesh protection could diminish the shock wave pressure to some extent, while an additional insulating epoxy resin layer enhanced it. Analysis results demonstrated that the pressure imposed on the laminated samples was related to the energy injected into the arc channel. In addition, the energy consumed by vaporized materials at the interface between the arc root and sample was defined as another source of shock wave pressure. The presence of an insulating layer confined the diffusion of the plasma channel at the arc root, as confirmed by high-speed imaging observations.

A series of nanoindentation tests were performed on a Zr-based bulk metallic glass at different peak-loads and strain rates. It is observed that the strain rate sensitivity index gradually decreases from positive to almost zero with increasing peak-load. Furthermore, at a fixed strain rate, the indentation hardness firstly shows a dramatic reduction and then becomes stable with increasing peak-load. These observations can be well understood in the framework of the activation and the accumulation of free volume via shear transformation zones. The current work may provide a practical way to tailor the hardness of the metallic glass.

A direct relationship between the yield strength and the atomic ratio of solvent (Zr) atoms in the Zr-Cu-Al-Ni metallic glasses system is firstly uncovered. It is found that either shear modulus or yield strength decreases almost nearly with the increase in atomic ratio of Zr. The origin of this relationship is ascribed to the preferential straining of the weakest configurations, which consist of the solvent-solvent bonds and the free volume concentrated in them. It is suggested that a higher atomic ratio of Zr corresponds to a larger amount of weakest configurations, which will facilitate the activation and the accumulation of the shear transformations and finally results in the lower yield strength. This finding may provide an effective strategy for designing high-strength metallic glasses by modifying the chemical composition.

To clarify the evolution of damage for typical carbon woven fabric/epoxy laminates exposed to lightning strike, artificial lightning testing on carbon woven fabric/epoxy laminates were conducted, damage was assessed using visual inspection and damage peeling approaches. Relationships between damage size and action integral were also elucidated. Results showed that damage appearance of carbon woven fabric/epoxy laminate presents circular distribution, and center of the circle located at the lightning attachment point approximately, there exist no damage projected area dislocations for different layers, visual damage territory represents maximum damage scope; visible damage can be categorized into five modes: resin ablation, fiber fracture and sublimation, delamination, ablation scallops and block-shaped ply-lift; delamination damage due to resin pyrolysis and internal pressure exist obvious distinguish; project area of total damage is linear with action integral for the same type specimens, that of resin ablation damage is linear with action integral, but no correlation with specimen type, for all specimens, damage depth is linear with logarithm of action integral. The coupled thermal–electrical model constructed is capable to simulate the ablation damage for carbon woven fabric/epoxy laminates exposed to simulated lightning current through experimental verification.