Search Results (13)

The trimodal grain-structured (TGS) carbon nanotube-reinforced aluminum matrix composites (CNT/Al) exhibit better strength–ductility synergy compared to bimodal grain-structured (BGS) composites. The addition of fine grain (FG) to the TGS composites effectively facilitates strain hardening and reduces strain/stress concentrations. In order to address the strain incompatibility in TGS composites, a significant accumulation of geometrically necessary dislocations (GNDs) occurs at the hetero-zone boundaries. This accumulation serves as the key factor in generating additional strengthening and work hardening. By utilizing a multi-mechanism strain gradient model, a quantitative analysis of the contributions made by Hall–Petch, Taylor, and back stress strengthening was conducted. Furthermore, effects of each domain volume fraction on the GND density at the boundaries between heterogeneous domains were carefully and extensively investigated and compared. It is found that the strengthening effect of back stress significantly surpasses that of the Hall–Petch and Taylor strengthening accounting. Compared to BGS composites, the TGS composites are more effective in facilitating strain hardening and reducing strain/stress concentrations, which may lead to a better balance between strength and ductility. Full article

Aluminum matrix composites (AMCs) with hetero-grains exhibit high strength with good ductility. A trimodal grain structure composed of ultrafine grains (UFGs), fine grains (FGs) and coarse grains (CGs) prevents the pre-mature cracking of hetero-zone boundaries in conventional bimodal grain structures; thus, it is favored by AMCs. However, the design of the size and distribution of hetero-domains in trimodal AMCs is tough, with complicated multi-scale deformation mechanisms. This study tunes the distribution of FG domains elaborately via altering the volume fraction of FG from 10 vol.% to 60 vol.% and investigates the distribution effect of FG domains on strength–ductility synergy. The optimized 2024 Al matrix composites with 30 vol.% FG exhibited a tensile strength of over 700 MPa and an elongation of 7.5%, respectively, realizing a good combination of high strength and ductility. This work enlightens the heterostructure design with a balance between heterogeneous deformation induced (HDI) strain hardening and high-content soft phase induced strain homogenization. Full article

The microstructures and mechanical properties of equiatomic CoCrFeMnNi high-entropy alloys (HEAs) treated with various processing parameters of laser surface heat treatment are studied in this paper. The typical inverse gradient-grained structure, which is composed of a hard central layer and a soft surface layer, can be obtained by laser surface heat treatment. A much narrower gradient layer leads to the highest yield strength by sacrificing ductility when the surface temperature of the laser-irradiated region remains at ~850 °C, whereas the fully recrystallized microstructure, which exists from the top surface layer to the ~1.05 mm depth layer, increases the ductility but decreases the yield strength as the maximum heating temperature rises to ~1050 °C. Significantly, the superior strength–ductility combination can be acquired by controlling the surface temperature of a laser-irradiated surface at ~1000 °C with a scanning speed of ~4 mm/s due to the effect of hetero-deformation-induced strengthening and hardening, as well as the enhanced interaction between dislocation and nanotwins by the hierarchical nanotwins. Therefore, retaining the partial recrystallized microstructure with a relatively high microhardness in the central layer, promoting the generation of hierarchical nanotwins, and increasing the volume proportion of gradient layer can effectively facilitate the inverse gradient-grained CoCrFeMnNi HEAs to exhibit a desirable strength–ductility synergy. Full article

Aqueous zinc ion batteries are highly sought after for the next generation of sustainable energy storage systems. However, their development is significantly impeded by the presence of undesired zinc dendrites, which greatly reduce their cycle life. It is well-received that surface passivation by introducing foreign metals represents a compelling measure to enhance the stability of Zn anodes. Nevertheless, the vast potential of effecting concerted interplay between multiple metal elements for enhanced overall performance in Zn ion batteries remains elusive, due to the overwhelming challenge in creating uniform textures from hetero-units and understanding the mechanism underlying the synergistic performance gain. In this work, an innovative bimetallic overlaying strategy is proposed that renders possible the synergy between AgZn₃ and CuZn₅ in effecting uniform Zn deposition in a laterally confined and compact manner. The seeded growth of Zn on the bimetal-modulated interface effectively reduces the nucleation potential barrier, yielding a low nucleation overpotential (25 mV). In full cell testing with a commercial MnO₂ applied as the cathode, superb cycling stability, surpassing the results reported in previous works, is achieved. The cell delivers an outstanding remaining capacity of 215 mA h g⁻¹ after 300 cycles with almost no capacity degradation observed. The simple and highly efficient bimetal design, which synergizes the strengths of distinct metals, has the potential to drive innovations in the development of multicomponent aqueous Zn batteries with exceptional performance. Full article

The as-extruded (EX) Mg-Gd-Y alloy studied here exhibited a bimodal structure, composed of fine dynamic recrystallized (DRXed) grains with random orientations and longitudinal coarse hot-worked grains. The slip analysis showed the DRXed grains exhibited mainly basal slips, while the hot-worked grains exhibited mainly prismatic slips during the tensile deformation. The distribution of geometrically necessary dislocations (GNDs) showed that there was strain partitioning between the fine and coarse grain regions. The hetero-deformation induced (HDI) hardening occurred between the two domains. It improves the strength and strain hardening capability of the alloy, leading to good strength-ductility synergy. Microcracks tended to nucleate at the DRXed grain boundaries, as well as at the interface between the two domains. The calculation of geometric compatibility parameter (m’) indicated that strain incompatibility between the adjacent grains induced the crack nucleation. The toughening effect of the fine DRXed grains hindered the crack propagation. However, the major crack formed at the interface between the two domains propagated unstably, due to the high stress concentration and the large crack size, causing the final failure. Full article

One of the most important issues in materials science is to overcome the strength–ductility trade-off in engineering alloys. The formation of heterogeneous and complex microstructures is a useful approach to achieving this purpose. In this investigation, a CoCrFeNiMn high-entropy alloy was processed via cold rolling followed by post-deformation annealing over a temperature range of 650–750 °C, which led to a wide range of grain sizes. Annealing at 650 °C led to the formation of a heterogeneous structure containing recrystallized areas with ultrafine and fine grains and non-recrystallized areas with an average size of ~75 μm. The processed material showed strength–ductility synergy with very high strengths of over ~1 GPa and uniform elongations of over 12%. Different deformation mechanisms such as dislocation slip, deformation twinning and hetero-deformation-induced hardening were responsible for achieving this mechanical property. Increasing the annealing temperature up to 700 °C facilitated the acquisition of bimodal grain size distributions of ~1.5 and ~6 μm, and the heterogeneous structure was eliminated via annealing at higher temperatures, which led to a significant decrease in strength. Full article

The increasing knowledge in nanoscience and materials technology promoted the development of advanced materials with enhanced and unusual properties suitable for sustainable applications ranging from energy to environmental purposes. Here are presented some results from our current investigations on composite semiconducting materials. The investigated composites have been prepared from different nitrogen precursors and thin films of TiO₂ nanotubes. The synergy between hetero-structures based on graphitic-C₃N₄ and thin films of titania nanotubes obtained by anodisation was studied. The composites have been characterised with several complementary techniques to evidence the relation between photo-behaviour and the composition of the samples. This study allows new insights into the nature of the specific enhanced properties due to this synergy among the two compounds. The g-C₃N₄/TiNT heterojunctions showed enhanced photo-electrochemical properties observed from the photocurrent measurements. The as-prepared composites have been investigated as cathode materials in the electrocatalytic reduction of oxalic acid (OX), evidencing the capability of tuning the reaction toward glycolic acid with respect to the pristine TiNT array. The observed Faradic efficiency (FE) for the composites follows the trend: TiNT-U₆ > TiNT-M₆ > TiNT-MU₁₈. TiNT-U₆ shows the best performances (FE_GC = 63.7%; FE_GO = 15.5%; OX conversion = 61. 4%) after 2 h of reaction. The improved photo-electrochemical properties make these materials suitable for H₂ production, solar-light-driven water splitting, and CO₂ reduction applications. Full article

Heterogeneous structures with both heterogeneous grain structure and dual phases have been designed and obtained in a high-Mn microband-induced plasticity (MBIP) steel. The heterogeneous structures show better synergy of strength and ductility as compared to the homogeneous structures. Higher contribution of hetero-deformation induced hardening to the overall strain hardening was observed and higher density of geometrically necessary dislocations were found to be induced at various domain boundaries in the heterogeneous structures, resulting in higher extra strain hardening for the observed better tensile properties as compared to the homogeneous structures. MBIP effect is found to be still effective in the coarse austenite grains of heterogeneous structures, while the typical Taylor lattice structure and the formation of microband are not observed in the ultra-fine austenite grains of heterogeneous structures, indicating that decreasing grain size might inhibit the occurrence of microbands. High density of dislocation is also observed in the interiors of BCC grains, indicating that both phases are deformable and can accommodate plastic deformation. It is interesting to note that the deformation mechanisms are highly dependent on the phase and grain size for the present MBIP steel with heterogeneous structures. Full article

Enzymes classified with the same Enzyme Commission (EC) that are allotted in different glycoside hydrolase (GH) families can display different mechanisms of action and substrate specificities. Therefore, the combination of different enzyme classes may not yield synergism during biomass hydrolysis, as the GH family allocation of the enzymes influences their behavior. As a result, it is important to understand which GH family combinations are compatible to gain knowledge on how to efficiently depolymerize biomass into fermentable sugars. We evaluated GH10 (Xyn10D and XT6) and GH11 (XynA and Xyn2A) β-xylanase performance alone and in combination with various GH family α-l-arabinofuranosidases (GH43 AXH-d and GH51 Abf51A) and α-d-glucuronidases (GH4 Agu4B and GH67 AguA) during xylan depolymerization. No synergistic enhancement in reducing sugar, xylose and glucuronic acid released from beechwood xylan was observed when xylanases were supplemented with either one of the glucuronidases, except between Xyn2A and AguA (1.1-fold reducing sugar increase). However, overall sugar release was significantly improved (≥1.1-fold reducing sugar increase) when xylanases were supplemented with either one of the arabinofuranosidases during wheat arabinoxylan degradation. Synergism appeared to result from the xylanases liberating xylo-oligomers, which are the preferred substrates of the terminal arabinofuranosyl-substituent debranching enzyme, Abf51A, allowing the exolytic β-xylosidase, SXA, to have access to the generated unbranched xylo-oligomers. Here, it was shown that arabinofuranosidases are key enzymes in the efficient saccharification of hetero-xylan into xylose. This study demonstrated that consideration of GH family affiliations of the carbohydrate-active enzymes (CAZymes) used to formulate synergistic enzyme cocktails is crucial for achieving efficient biomass saccharification. Full article

The tensile properties and the corresponding deformation mechanism of the graded 304 stainless steel (ss) at both room and cryogenic temperatures were investigated and compared with those of the coarse-grained (CGed) 304 ss. Gradient structures were found to have excellent synergy of strength and ductility at room temperature, and both the yield strength and the uniform elongation were found to be simultaneously improved at cryogenic temperature in the gradient structures, as compared to those for the CG sample. The hetero-deformation-induced (HDI) hardening was found to play a more important role in the gradient structures as compared to the CG sample and be more obvious at cryogenic temperature as compared to that at room temperature. The central layer in the gradient structures provides stronger strain hardening during tensile deformation at both temperatures, due to more volume fraction of martensitic transformation. The volume fraction of martensitic transformation in the gradient structures was found to be much higher at cryogenic temperature, resulting in a much stronger strain hardening at cryogenic temperature. The amount of martensitic transformation at the central layer of the gradient structures is observed to be even higher than that for the CG sample at cryogenic temperature, which is one of the origins for the simultaneous improvement of strength and ductility by the gradient structures at cryogenic temperature. Full article

The demand for tailored, micrometer-scaled biomaterials in cell biology and (cell-free) biotechnology has led to the development of tunable microgel systems based on natural polymers, such as hyaluronic acid (HA). To precisely tailor their physicochemical and mechanical properties and thus to address the need for well-defined microgel systems, in this study, a bottom-up material guide is presented that highlights the synergy between highly selective bio-orthogonal click chemistry strategies and the versatility of a droplet microfluidics (MF)-assisted microgel design. By employing MF, microgels based on modified HA-derivates and homobifunctional poly(ethylene glycol) (PEG)-crosslinkers are prepared via three different types of click reaction: Diels–Alder [4 + 2] cycloaddition, strain-promoted azide-alkyne cycloaddition (SPAAC), and UV-initiated thiol–ene reaction. First, chemical modification strategies of HA are screened in-depth. Beyond the microfluidic processing of HA-derivates yielding monodisperse microgels, in an analytical study, we show that their physicochemical and mechanical properties—e.g., permeability, (thermo)stability, and elasticity—can be systematically adapted with respect to the type of click reaction and PEG-crosslinker concentration. In addition, we highlight the versatility of our HA-microgel design by preparing non-spherical microgels and introduce, for the first time, a selective, hetero-trifunctional HA-based microgel system with multiple binding sites. As a result, a holistic material guide is provided to tailor fundamental properties of HA-microgels for their potential application in cell biology and (cell-free) biotechnology. Full article

Tetrahydropyran (THP) represents an O-containing hetero-cyclic compound that can be used as a promising solvent or monomer for polymer synthesis. In this work, Cu–ZnO/Al₂O₃ catalysts have been prepared by a facile precipitation–extrusion method and used for the synthesis of THP through gaseous-phase hydrogenolysis of tetrahydrofurfuryl alcohol (THFA). The effect of the molar ratio of Cu/Zn/Al, reaction temperature, and hydrogen pressure was investigated. An 89.4% selectivity of THP was achieved at 270 °C and 1.0 MPa H₂. Meanwhile, the optimum molar ratio of Cu/Zn/Al was determined to be 4:1:10. The Cu–ZnO/Al₂O₃ catalyst exhibited high catalytic activity and stability for 205 h on-stream. A possible reaction mechanism involving several consecutive reactions was proposed: THFA was firstly rearranged to 2-hydroxytetrahydropyran (2-HTHP), followed by the dehydration of 2-HTHP to 3,4-2H-dihydropyran (DHP) over acid sites; finally, the DHP was hydrogenated to THP. The synergy of acid sites and metal sites of Cu–ZnO/Al₂O₃ played an important role during the production of THP. Full article

Bimetallic nanoparticles represent attractive catalytic systems thanks to the synergy between both partners at the atomic level, mainly induced by electronic effects which in turn are associated with the corresponding structures (alloy, core-shell, hetero-dimer). This type of engineered material can trigger changes in the kinetics of catalyzed processes by variations on the electrophilicity/nucleophilicity of the metal centers involved and also promote cooperative effects to foster organic transformations, including multi-component and multi-step processes. Solvents become a crucial factor in the conception of catalytic processes, not only due to their environmental impact, but also because they can preserve the bimetallic structure during the catalytic reaction and therefore increase the catalyst life-time. In this frame, the present review focuses on the recent works described in the literature concerning the synthesis of bimetallic nanoparticles in non-conventional solvents, i.e., other than common volatile compounds, for catalytic applications. Full article