查看更多>>摘要:? 2022 Elsevier B.V.The effect of pre-strain treatment on mechanical properties of a Ni-Co base disk superalloy was studied. Results show that the pre-strain treatment, creep at 725 °C/630 MPa, improves the yield strength of the alloy at 23 °C and 760 °C. However, the creep life (at 760 °C/480 MPa) of the alloy was reduced by pre-strain treatment. The microstructure indicated that a lot of microtwins and Suzuki segregations were introduced by the pre-strain treatment, besides some unfavorable factors on mechanical properties, i.e., ripening of precipitates. The interactions of microtwin and Suzuki segregation with dislocations were discussed in this study, and it was deemed that the impediment of twin boundary and Suzuki segregation to the motion of dislocation may be responsible for the enhancement of the mechanical properties. Meanwhile, the microtwin and the Suzuki segregation have good stability at service temperature. If the problem of reducing the creep properties caused by pre-strain treatment would be solved, the introduction of microtwin and Suzuki segregation appropriately can be considered as a novel strengthening method in designing advanced superalloys.
查看更多>>摘要:? 2022 Elsevier B.V.In this study, a MoS2/ZnO heterostructure with type-II band alignment was successfully synthesized via a simple hydrothermal and sol-gel spin-coating method using a MoS2 added precursor solution. The surface of the MoS2/ZnO thin films consisted of MoS2 particles. In addition, type-II band alignment was observed at the interface between ZnO and MoS2, which facilitated the transfer of electrons and holes under UV illumination. With respect to UV photoresponse characteristics, the MoS2/ZnO thin films with the MoS2 concentration of 0.2 M showed significantly higher photocurrent than all the other thin films investigated. In addition, these thin films showed faster UV photoresponse and highly improved photoresponsivity, photosensitivity, and photoselectivity. Thus, the MoS2 concentration of 0.2 M was found to be optimum for the preparation of MoS2/ZnO heterojunction thin films with excellent UV photoresponse characteristics to overcome the limitations of ZnO-based UV photodetectors.
查看更多>>摘要:? 2022 Elsevier B.V.Decreasing the desorption temperature and formation enthalpy are two key challenges for the practical application of magnesium-based hydrogen storage materials. In this paper, different Mg2Ni samples were successfully synthesized, and the corresponding hydrogen storage kinetic and thermodynamic behaviors were investigated. The carbon-covered nanocrystalline Mg2Ni started to take up hydrogen at room temperature and released hydrogen at 180 °C. Meanwhile, the hydrogenated sample fully desorbed hydrogen at 250 °C within 10 min, and absorbed 2.1 wt% hydrogen in 1 h at 125 °C. The absorption and desorption activation energy of carbon-covered nanocrystalline Mg2Ni was calculated to be 20.8 ± 1.2 kJ/mol and 34.1 ± 2.4 kJ/mol, which were 74% and 78% lower than that of MgH2, respectively. The dehydrogenation enthalpy of the carbon-covered nanocrystalline Mg2NiH4 sample was also reduced from 89.9 ± 4.0 kJ/mol of MgH2 to 67.0 ± 0.5 kJ/mol. In addition, the cycling kinetics was maintained after ten cycles. Further analysis revealed that the remarkably improved hydrogen storage property of Mg2NiH4 originated from the combining effect of the alloying, carbon covering, and nanocrystalline strategy.
查看更多>>摘要:? 2022 Elsevier B.V.Al-7Si-0.6Mg/Fe bimetal was prepared by compound casting; it was heat-treated to investigate the age-hardening behavior of the aluminum matrix near the interface. Metallurgical bonding of the interface is accompanied by the formation of an oxide layer in the aluminum matrix near the interface. The intermetallic layer grows at the expense of the Si and Mg2Si particles within the diffusion reach during the solution heat treatment. The fraction of both AlFeSi and Si is low near the interface, the fraction of the AlFeSi phase is the highest just outside the oxide layer and decreases with increasing distance from the interface, which is accompanied by the increase in the fraction of the Si phase. The presence of the continuous oxide layer decreases the age-hardening ability and bonding strength of the aluminum matrix near the bimetal interface; such a negative effect is mitigated by the broken oxide layer. The lower age-hardening ability is resulted from the segregation of the Mg element to the oxide layer.
查看更多>>摘要:? 2022 Elsevier B.V.The searching for new memory that can work under harsh conditions will be significant for their application in some important fields such as geothermal, oil and aerospace industries. In this work, memory devices with simple sandwich structures using the g-C3N4 treated by different concentration acids as active layers have been fabricated, which exhibit non-volatile behaviors and bipolar switching characteristics. Protonation treatment can enhance the memory performance efficiently compared with un-protonized device. Among them, the device containing g-C3N4 treated with 8 M HCl presents the best resistive switching performance with ON/OFF ratio of 104 and good retention capability, which might be relative to its texture without violent tortuosity. In addition, the protonated g-C3N4-based memory devices exhibit good environmental robustness, including temperature and ionizing irradiation. Specially, its high tolerant temperature (454 °C) can also be assisted by doping BN for heat dissipation. Their good thermal/irradiating stabilities are assigned to the strong bond energy of C[dbnd]N double bonds localized π-conjugated tri-s-triazine rings. In all, the facial protonation treatment without any functionalization or supporting, the simple sandwich device structure and good environmental robustness endow their promising applications in aerospace and outdoor environment.
查看更多>>摘要:? 2022 Elsevier B.V.MXenes are attracting great interest for their excellent electrical and mechanical properties. High dielectric constants have been achieved in polymer-based nanocomposites with MXenes as fillers, but these materials suffer from large dielectric losses. In this work, Ti3C2Tx MXene/silicone rubber (SR) nanocomposites were prepared because of the low dielectric loss of SR. The effects of Ti3C2Tx MXene nanosheets on the thermal stability, dielectric and mechanical performance of the nanocomposites were investigated. A dielectric constant of 6.2 accompanied by an extremely low dielectric loss of 0.001 at 103 Hz frequency was obtained in the nanocomposites when 1.2 wt% Ti3C2Tx MXene was loaded. The enhanced dielectric properties are mainly attributed to the Maxwell-Wagner-Sillars effect and the microcapacitor model. Moreover, the thermal stability of the nanocomposites can reach 450 °C. Tensile strength of 430 kPa, elongation at break of 341% and reduced elastic module of 402 kPa were also obtained in the nanocomposite with 2 wt% Ti3C2Tx MXene. This work provides a method for fabricating polymer-based nanocomposites with excellent dielectric properties under low filling content, which is crucial for modern electronic applications.
查看更多>>摘要:? 2022 Elsevier B.V.Metal hydrides were discovered in the fifties and since then have been widely studied and developed, mainly for energy applications (batteries, hydrogen storage, compression.). In addition to these uses, other properties are considered such as sensors, actuators, or scavengers. This paper proposes a review of intermetallic-based materials for hydrogen gettering. The different chemistries (Zr- or Ti-based compounds) are described in terms of alloying elements and gettering properties. Various aspects, including the activation process, surface coating and resistance to impurities, are also discussed. Finally, new processes and other possible applications are discussed for these materials.
查看更多>>摘要:? 2022Ceramic coated metal powders have recently found prominence owing to their prospective application in 3D microstructured metal matrix composite synthesis. To ensure a perfect matrix-reinforcement interface in these composites, the coating process needs to be in situ. To that end, we recently developed a process for in situ nitride surface coating of CoCrFeNi high entropy alloy (HEA) powder. This approach offers various advantages over other processes including ease of controlling the surface morphology and compositional control by adjusting the nitriding parameters. In this study, we aimed to elaborate the nitride layer formation mechanism, growth kinetics, and compositional control. Mechanically alloyed CoCrFeNiTi0.5 HEA powder was used as the starting powder. The nitride layer growth on the powder was observed at different temperatures of 973, 1073 and 1173 K for 1–12 h under partial nitrogen atmosphere. The nitrogen preferentially reacted with Ti to form a continuous layer of TiN on the powder surface. Further growth was found to be diffusion-controlled by the growth rate increase with increasing nitriding temperature. Morphological investigation revealed a strong efflux of Ti through the TiN grain boundaries resulting in a scale growth at the TiN/gas interface. This growth mechanism was validated by a high TiN layer growth activation of 240 kJ.mol?1. Finally it was revealed that the Cr dissolution within the TiN layer can be achieved at higher temperature. However, to retain the integrity of the surface layer, the Cr dissolution process needs better control
查看更多>>摘要:? 2022The transition-metal-based alloy and chalcogenides have been widely investigated as efficient sulfur host for lithium sulfur batteries (LSB), yet the synergistic effect of both has been rarely reported. Herein, nickel cobalt alloy (NiCo) and nickel cobalt sulfides (NiCoS) have been simultaneously constructed on the nitrogen-doped carbon substrate (NiCo-NiCoS/NC) via facile calcination-sulfurization of NiCo Prussian blue analogue (NiCo-PBA). The abundantly exposed NiCo alloy and NiCoS domains act as adsorption and catalytic sites that enable effective capture and catalytic conversion of polysulfides, and the highly conductive NiCo-NiCoS integrated with N-doped carbon provides a facile Li+ transfer channel. As a result, S@NiCo-NiCoS/NC electrode delivers a high initial discharge capacity of 1345.1 mA h g?1 at the current density of 0.1 C, superior rate capability of 692.1 mA h g?1 up to 5 C, and ultralong lifespan over 1500 cycles with a small capacity decay of 0.055% per cycle at the current density of 1.0 C.
查看更多>>摘要:? 2022 Elsevier B.V.The synergistic effects of copper addition and hot extrusion process on the modification of microstructure and enhancement of mechanical properties of a common in situ hypereutectic Mg-Si metal-matrix composite were studied. It was revealed that Cu addition at the microalloying level of 0.5 wt% was very effective in modifying the primary and eutectic Mg2Si phases, which led to the enhancement of the as-cast mechanical properties. Further Cu additions (2, 4.5, 8, and 15 wt%) led to the appearance of the α-Mg/Mg2Cu eutectic constituent and distinct α-Mg regions with the disappearance of Mg2Si eutectics in the ingots, which was ascribed to the change in the solidification path. Contrary to the favorable effect of Cu at the micro-addition level, higher additions led to poor tensile properties due to the deleterious effect of eutectics. Fragmentation and dispersion of intermetallics, as well as intense grain refinement by dynamic recrystallization (DRX) were observed for the extruded composites due to the hot deformation effects, which resulted in the enhancement of the ultimate tensile strength, total elongation, and tensile toughness. Accordingly, it was concluded that Cu addition to Mg-Si composites should be limited to small amounts for modification effects, and if it is combined with the elevated-temperature thermomechanical processing, the optimum strength-ductility trade-off can be achieved.