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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.

Grain-boundary (GB) precipitation has a significant adverse effect on plasticity of alloys, which easily leads to catastrophic intergranular failure in safety-critical applications under high external loading. Herein, we report a novel strategy that uses the local stress concentration induced by GB precipitates as a driving force to trigger phase transformation of preset non-equiatomic high-entropy solid-solution phase at GBs. This in situ deformation-induced phase transformation at GBs introduces a well-known effect: transformation-induced plasticity (TRIP), which enables an exceptional elongation to fracture (above 38 %) at a high strength (above 1.5 GPa) in a GB precipitation-hardened high-entropy alloy (HEA). The present strategy in terms of “local stress concentration-induced phase transformations at GBs” may provide a fundamental approach by taking advantage of (rather than avoiding) the GB precipitation to gain a superior combination of high strength and high ductility in HEAs.

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 aircraft lightning environment consists of four lightning current components with different parameters, which are known as lightning components A, B, C and D. The lightning damage of aeronautic carbon fiber reinforced polymer laminates subjected to multiple continuous sequential lightning current components with different timing combinations was experimentally evaluated. The experimental results indicated that the carbon fiber reinforced polymer laminates suffered serious lightning damage, including carbon fiber fracture, resin pyrolysis and delamination. Through an analysis of the lightning damage properties of carbon fiber reinforced polymers, the influential factors and evaluation methods of the lightning damage in carbon fiber reinforced polymer laminates were studied. Because the lightning damage evaluation method under a single lightning impulse was found to be inapplicable for the multiple continuous lightning strikes, a multi-factor evaluation method was proposed. In the multiple continuous lightning strike test, the damage depth was found to be closely related to lightning components A, B and D and could be estimated based on the amplitudes and rise rates of the applied lightning components. Increases in the damaged area after a lightning strike were driven by lightning component C due to its substantial thermal effects. The damaged area was evaluated on the basis of the parameters of the electrical action integral and the transfer charge. The research on the evaluation methods for carbon fiber reinforced polymer laminate lightning damage presented herein may provide experimental support and a theoretical basis for studying the lightning effect mechanism and optimizing material formulations, manufacturing processes and structural designs to achieve performance improvements for carbon fiber reinforced polymer laminates in the future.

Microstructures and mechanical properties of homogenized Al-2.5 wt% Cu (Al-Cu), Al-2.5 wt%Cu-0.3 wt%Sc (Al-Cu-Sc) and Al-2.5 wt%Cu-0.3 wt%Sc-0.2 wt% Fe (Al-Cu-Sc-Fe) alloys were comprehensively studied, which allowed to demonstrate the single Sc effect as well as the combined Sc and Fe effect on microstructural evolution during homogenization treatment and hence on mechanical response, respectively. It was clearly revealed that the single minor Sc addition refined the grains of as-cast Al-Cu alloy, and induced Sc enrichment in the micro-sized α-Al/θ-Al2Cu eutectic. During homogenization, the Sc distribution highly affected the formation of micron-sized (Cu,Sc)-rich W-phases and submicro/nano-sized Al3Sc dispersoids. In comparison, the co-addition of minor Fe and Sc produced grains and micro Sc-segregation similar to the single Sc addition. However, the formation of W phase was highly suppressed. This resulted in promoted Al3Sc dispersoid formation during homogenization and led to improved strength. Unfortunately, coarse (Cu, Fe)-rich constituents were newly created in the homogenized Al-Cu-Sc-Fe alloy, and the ductility of alloy was correspondingly reduced.

The mechanical behavior of (Fe40Mn40Co10Cr10)100−xCx (x = 0, 2.2, 3.3 at.%) high entropy alloys (HEA) at various temperatures (298 K, 159 K and 77 K) was investigated. For Fe40Mn40Co10Cr10 HEA, the jointly activated twinning and martensitic phase transformation concurrently increase the strength and ductility at 77 K. In contrast, twinning and phase transformation gradually vanish as temperature decreases for carbon alloyed HEAs, resulting in ductile-brittle transition. Our findings indicate that the additional interstitial carbon atoms increase the f.c.c. phase stability, and inhibit the deformability of Fe40Mn40Co10Cr10 HEA at low temperature.

The microstructure and mechanical properties of powder-forged Fe-C-Cu alloys manufactured at an elevated temperature were evaluated. It was found that the mechanical properties of the alloys were no worse than those in the literature, and the contribution of copper to the strength was quantified: the major strengthening mechanism of copper is grain-refinement strengthening rather than precipitation strengthening. Then, to ensure the safety of the elevated-temperature manufacturing, the hot-deformation behaviour of the Fe-C-2.5Cu alloy was investigated via construction of the constitutive equation and the hot-processing map, which proved that the high-temperature manufacturing was not only safe but also efficient. Finally, fatigue tests were conducted on the powder-forged connecting rods and 5154 wrought steel connecting rods for the same engine application, and the results showed that the powder-forged connecting rods had better fatigue strength and higher reliability.