查看更多>>摘要：? 2022 Elsevier B.V.S-vacancy in MoS2 is known to enhance its HER activity but its creation by simple synthetic methods are yet to be explored. In this correspondence, we present a viable methodology for the synthesis of multilayered MoS2 and Sn doped MoS2 nanosheets having S deficiency. Sn doping in MoS2 lattice is confirmed by X-ray diffraction and Raman analysis. The surface morphological characteristic of the samples and valence states of the elements are examined using FESEM with EDAX, TEM and XPS analysis respectively. A reduction of 187 mV in the overpotential was observed for the Sn doped MoS2 accompanied by a significant decrease in Tafel slope which is attributed to the S-vacancy induced active sites. The obtained overpotential and Tafel slope values are in close resemblance with that of some of the reported exfoliated and few-layered MoS2.
查看更多>>摘要：? 2022 Elsevier B.V.Searching for preeminent electrocatalysts toward hydrogen evolution reaction (HER) is significantly important in transforming renewable electricity to clean hydrogen energy by electrochemical water splitting. Herein, ultrafine RuPd alloy nanoparticles anchored in MOFs-derived N-doped porous carbon dodecahedrons (RuxPd1?x @NPC) were synthesized by microwave-assisted ethylene glycol reduction method. Due to the synergistic promotion by modulating the composition and structure, excellent HER catalytic performance was achieved in both alkaline and acidic media for the as-prepared RuxPd1?x @NPC electrocatalysts with low noble metal loading. In which, Ru0.7Pd0.3 @NPC exhibited significantly enhanced alkaline HER activity with a low overpotential of only 20 mV to reach a current density of 10 mA cm?2. Meanwhile, Ru0.3Pd0.7 @NPC showed admirable HER activity in acidic media, which delivered an overpotential of 36 mV at 10 mA cm?2. Additionally, the proposed catalysts demonstrated high mass activity and good long-term stability in both alkaline and acidic condition, remarkably surpassing the commercial Pt/C catalyst. The superior activity of the RuxPd1?x @NPC catalysts is attributed to improved intrinsic activity, fast charge transfer kinetics and distinct electrochemical active surface areas after alloying. This work provides a rapid and facile synthesis of highly efficient, durable and affordable alloy electrocatalysts for hydrogen evolution.
查看更多>>摘要：? 2022 Elsevier B.V.In order to accelerate the hydrogen absorption and desorption rates of hyper-eutectic Mg-Ni alloy, Mg85Ni15-xAgx (x = 0, 0.2, 0.4, 0.6) alloys were prepared and the results show that fishbone eutectic was formed without change of phase composition. It was found that Ag atoms were dissolved in fishbone eutectic Mg2Ni and the average cell parameters of Mg2Ni increase with the increase of Ag content. Owing to adjusting lattice parameters, the hydrogen absorption and desorption rates of Mg85Ni14.8Ag0.2 alloy are significantly improved. About 4.47 wt% hydrogen is absorbed at 275 ℃ only in 1 min, with the maximum capacity of 5.84 wt% in 60 min. The Mg85Ni15-xAgx (x = 0.2, 0.4, 0.6) hydrides can be completely dehydrogenated within 10 min at 275 ℃. The corresponding activation energies for dehydrogenation are determined to be 80.4, 97.1 and 97.8 kJ/mol, respectively, which are lower than 117.8 kJ/mol of Mg85Ni15. The onset dehydrogenation temperature of Mg85Ni14.8Ag0.2 hydride is reduced to 201 ℃, which is much lower than 220 ℃ of the Mg85Ni15 hydride. The dissolving of Ag in Mg2Ni leads to a lattice expansion, which facilitates the diffusion for hydrogen atoms and decrease the energy barrier required for nucleation of Mg/Mg2Ni. As a result, the hydrogen de-/absorption rates were obvious accelerated and the onset dehydrogenation temperature was decreased.
查看更多>>摘要：? 2022 Elsevier B.V.The microstructure and phase composition of the EBAM Ti-6Al-4 V alloy samples were studied by the methods of in situ high temperature synchrotron X-ray diffraction and transmission electron microscopy (TEM) during heating from room temperature to a temperature of 1373 K. In the initial state, the main phase of the EBAM Ti-6Al-4 V alloy the samples was the α phase, the second phases were β + α″. The volume fraction of the β phase does not exceed 5%, α″ - 3%. It was found that the new α″ phase was formed at the temperature of 1073 K due to the phase transition α→α″. The α″ phase volume fraction increased as the heating temperature increased to the temperature of 1223 K and then decreased with a further increase of the temperature due to the α″→β phase transition. The dependences of the lattice parameters of the α, β and α″ phases on the heating temperature were revealed. It was established that the crystal lattice of the α phase was distorted during heating. The α phase passed into the unstable state. An increase of the c/a parameters ratio was accompanied by the formation of the α″ and β phases.
查看更多>>摘要：? 2022Microstructures, phase transformations and mechanical properties of the Ti-48Al-2Cr-2Nb-xHf (4822-xHf, x = 0, 2, 4, 6 at%) intermetallic alloys were investigated. The alloys were fabricated by vacuum arc remelting followed by hot isostatic pressing and homogenization treatment. The results showed that Hf alloying leads to a significant microstructure refinement in terms of both colony size and inter-lamellar spacing. Homogenization at 1400 °C resulted in a fully lamellar (FL) microstructure in 4822 and 2Hf alloys, while nearly lamellar (NL) in 4Hf and 6Hf alloys. Differential thermal analysis (DTA) demonstrated that Hf addition up to 2 at% has a slight contribution to phase transition sequences, but a significant implication to the phase equilibrium of the alloys with further Hf content. Based on the DTA data and annealing at 1450 °C, the solvus temperature of the eutectic phases was estimated to be over the range of 1430–1440 °C. Although the eutectic phases of Al3Hf2 and TiAl2 formed during solidification of the high-Hf alloys did not undergo any phase transition, both size and volume fraction of the eutectic cells increased due to the solvus of these metastable eutectic phases. The orientation relationship {111}Tetragonal//{001}Orthorhombic detected between the eutectic phases and their surrounding matrix confirmed the occurrence of γc (TiAl) → eutectics (Al3Hf2, TiAl2) phase transformation. Small punch tests results showed that the 2Hf and 4Hf alloys exhibit a higher maximum load (Fm) than the base 4822 alloy due to the solid solution effect of Hf and finer inter-lamellar spacing. Nevertheless, the brittle behavior of the eutectic phases dramatically deteriorated mechanical performance such that the 6Hf alloy possessed the lowest Fm and displacement. The major fracture mode changed from trans-lamellar to inter-lamellar as the Hf content increased from 4 to 6 at%.
查看更多>>摘要：? 2022 Elsevier B.V.In this paper, the aging behavior of Cf(Ni)-ZrC/2024Al composites with a quasi-network structure was studied carefully. The microstructure observation exhibits that the ZrC particles, carbon fibers, and Al matrix form a good interface bonding. The interfacial phase between the carbon fiber and Al matrix exhibits good thermostability during solution and aging treatment. With the addition of carbon fibers and ZrC particles, the composites only take 8 h to reach peak-aged condition while in monolithic 2024Al alloy, it needs 12 h. The peak-aged hardness of the composites is 136.4 HV, having 15.2% increments than 2024Al (118.4 HV). The yield, tensile strength, and strain of the peak-aged composites are 350.5 MPa, 536.4 MPa, and 14.8% respectively, which are improved by 56.5%, 45.8%, and 52.6% compared with 2024Al. The yield and tensile strength of composites are increased with time going by until they reach a peak aging state, agreeing well with that of hardness. The TEM observations of precipitated phases demonstrate the size and number of Al2Cu and Al2CuMg present a similar variation tendency. The improved tensile property of the composites is mainly due to pulled-out carbon fibers, quasi-network structure, outstanding interface bond, and precipitate strengthening.
查看更多>>摘要：? 2022 Elsevier B.V.A particular dual-layer structure of reinforced anti-corrosion magnesium aluminum-layered double hydroxide-Zn-G/Ni coating (LDH-ZGN), grown in situ the magnesium aluminum-layered double hydroxide coating (LDH) on the surface of the magnesium alloy, and a Zn-G/Ni composite coating was deposited on the LDH coating by low-pressure cold gas spraying (LPCGS). The LDH-ZGN was characterized by XRD, XPS, SEM, EDS, etc. The coating's corrosion protection and enhancement effect were explored through the electrochemical test of polarization curve, EIS, and coating immersion test. LDH-ZGN exhibited excellent corrosion resistance, mainly attributed to the synergy between reduced graphene oxide (rGO) and magnesium aluminum-layered double hydroxides (MgAl-LDH) and the enhancement effect of the coating under the particular dual-layer structure.
查看更多>>摘要：? 2022In this work, the evolution process, crystallinity, microstructure and morphology of Mg-9Gd-2Y-0.5Zn-0.5Zr (wt%) alloy precipitates were analyzed during isothermal aging at 200 ℃. During the early stages of aging, the precipitate phase distributed in the matrix is mainly the β′′ phase, which exhibits a hexagonal D019 structure. In the peak-aged stage, the γ′′ phase, LPSO phase, and β′ of the precipitates coexist in the matrix. The synergism between the three types of phases is significant with respect to the improved age-hardening. We propose that the optimized mechanical properties of the alloy originate from the co-precipitation of the LPSO, β′, and γ'' phases. Furthermore, it is an important way to improve the performance of the alloy at high temperatures.
查看更多>>摘要：? 2022 Elsevier B.V.The superior mechanical properties and thermal stability of Ti-Al-Si-N coatings have attracted extensive research interests in academia as well as industry. In this study, Ti0.52Al0.48N, Ti0.53Al0.38Si0.09N, Ti0.43Al0.48Si0.09N, and Ti0.48Al0.38Si0.14N coatings are developed by arc-evaporation. This compositional variation allows to study the impact of Al and Si on structure, thermal stability, and oxidation behavior. Incorporation of Si into Ti-Al-N leads to a nanocomposite structure with an amorphous-like SiNx boundary-phase – encapsulating small crystalline Ti-Al-N grains – and promotes wurtzite-type AlN formation. This causes a significant change in the mechanical and thermal properties of the originally single-phase face-centered cubic structured Ti0.52Al0.48N. The Si-containing coatings experience an initial increase in hardness from 29.1 ± 1.0 GPa for Ti0.52Al0.48N to 33.1 ± 1.2 GPa for Ti0.53Al0.38Si0.09N, and then a decrease to 26.4 ± 0.8 GPa for Ti0.43Al0.48Si0.09N and 28.1 ± 0.8 GPa for Ti0.48Al0.38Si0.14N. Alloying with Si improves the thermal stability of Ti-Al-N by retarding the decomposition towards its thermodynamically stable constituents TiN and AlN. Moreover, the oxidation resistance of Ti-Al-N can be largely improved by the Si-addition due to the retarded anatase-to-rutile TiO2 transformation as well as the formation of a protective oxide scale at the nitride-to-oxide interface. Cross-sectional scanning electron microscopy studies reveal that the oxide scales of the Si-containing coatings exhibit a lamellar structure comprising Al-rich, TiSi-rich, and/or Ti-rich oxide layers. Higher Si and, especially, higher Al content is favorable to the formation of an Al-rich layer, which can act as a diffusion barrier for oxygen. Especially, all Si-containing coatings present an abnormal oxidation behavior, where the consumed nitride layer thickness is not continuously increasing with oxidation temperature.
查看更多>>摘要：? 2022Understanding interaction between interstitial elements and matrix at the bulk phases and phase interfaces is crucial in alloy design. In this study, using first-principles density functional theory, we investigate the effect of interstitial elements (B, N, and C) on electronic structures and elastic properties for the primary γ-TiAl and α2-Ti3Al phases of TiAl alloys. It shows that N has the highest solid solubility than B and C based on the calculation of energy and corresponding experimental results, implying that it has the strongest interaction with the matrix simultaneously. The Cottrell atmosphere induced by interstitial elements can be intensified by increasing the bonding strength as it would significantly improve the strength of the alloys. The N element would increase the interfacial separation energy, strengthen the interfaces, facilitate dislocation pile-ups, and finally strengthen the interfaces of TiAl alloys. Moreover, the N element also enhances the toughness of the phase to the highest degree according to B/G. For Nb-rich TiAl alloys, Nb promoting the formation of Ti anti-site sites can facilitate solid solubility of interstitial elements and strengthen their bond with the nearest adjacent atoms in the matrix. The theoretical results were further confirmed by experiments.
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