查看更多>>摘要：The balance between the mechanical properties and corrosion resistance of high strength 7xxx Al alloys is an important topic. This study introduced pre-rolling into the solution and aging treatments for a recently developed 7A99 Al. The cold rolling after solution but before aging was considered as the first group, and the cold rolling before solution was the second group. For the first group, a great deal of strain energy was stored in the alloy, which contributed the occurrence of recrystallization during subsequent solution process and a finer grain structure. For the second group, the dislocations induced by cold rolling before aging accelerated the coarsening of η' and η precipitates. Moreover, T76 aging also caused the larger size of precipitates due to its higher temperature than T6 aging. The pitting corrosion of 7A99 Al tended to initiate at Al_7Cu_2Fe intermetallic, and the dissolution of MgZn_2 phase along grain boundaries facilitated the in-tergranular corrosion. The cold rolling after solution process and T76 treatment both improved the resistance on stress corrosion cracking, since the grain boundary precipitates had large size, discontinuous distribution and high Cu content. The combining of cold rolling before solution and T6 treatment contributed to the enhancement of strength due to the fine grain strengthening, solution strengthening and precipitates strengthening, and the corresponding yield strength and ultimate tensile strength reached as high as 628 and 665 MPa. Compared to T6 treatment, the strength of T76 treated samples was reduced only by 3-5%, which is an advantage of the proposed method.
查看更多>>摘要：The hot deformation behaviour of Al-Sil2CulMgl alloy foam, Al-Sil2CulMgl alloy-single-wall carbon nanotubes (SWNTs), Al-Sil2CulMgl-cenospheres, and Al-Sil2CulMgl-cenosphere-SWNTs hybrid foams (HFs) were investigated at different test temperatures (25-400 °C) and strain rates (10~(-3)-1 s~(-1)) conditions. It is observed that the energy absorption capacity of all the foams decreased with an increased test temperature (TT) whereas it increased with an increase in strain rate. The hybrid foam in which the cenosphere and SWNTs were added together exhibited the highest plateau stress and energy absorption amongst all investigated foams. The strain rate sensitivity and activation energy for each kind of foam was calculated as a function of temperature and strain rate. The activation energy data tells that the deformation mechanism is dominated by vacancy and dislocation diffusion at TT< 200 °C regardless of the type of foam, strain rate and relative density. On the other hand, the deformation mechanism is dominated by dynamic recovery and recrystallization when the TT increase beyond 200 °C (TT > 200 °C). This study further demonstrates the synergistic effect of cenosphere and SWNTs on enhancing the plateau stress and energy absorption of HFs.
查看更多>>摘要：Ever-harsher service environments in the future will call for systematic studies on service behaviors of high-entropy alloys (HEAs) under multi-field coupling. Instead of focusing solely on service behaviors under conventional conditions, the promoted serration behavior of Al_(0.1)CoCrFeNi HEA, commonly known as Portevin-Le Chatelier (PLC) effect, under coupled electron-heat field was quantitatively analyzed in terms of several characteristic parameters in this work. The obvious PLC phenomenon with severe serration can boost the decrease of tensile strength and elongation in the service environment of coupled electron-heat. Our results indicate that this macroscopic serrated behavior can be rationalized by defect-level micro-structural interaction, namely the enhanced repetitive pinning and de-pinning effect of solute atoms on mobile dislocations, according to the mechanism of dynamic strain aging. This was proved by the increased kinking and bowing morphologies of dislocations, as well as abundant stacking faults under coupled electron-heat field.
查看更多>>摘要：Mn_3O_4 is viewed as an attractive candidate for rechargeable aqueous zinc-ion battery cathode materials due to the advantages of low cost, eco-friendly nature as well as high capacity. However, it faces inherently poor electronic conductivity and poor cyclability during battery cycling. To improve the electrochemical performance, Mn_3O_4 nanoparticles anchored on carbon nanotubes (CNTs@Mn_3O_4) were fabricated by a facile one-step solution process at low temperature. Benefiting from the synergistic effect of nanoscale Mn_3O_4 and 1D CNTs, the conductivity and electrochemical performance of Mn_3O_4 are significantly improved. The prepared CNTs@Mn_3O_4 nanocomposites deliver a discharge capacity of 310 mAh g~(-1) at 100 mA g~(-1) and maintain 123 mAh g~(-1) at 1000 mA g~(-1) after 500 cycles, demonstrating good rate capability and cycling performance as a promising cathode material for low-cost neutral zinc-ion battery.
查看更多>>摘要：In this work, metal-free hexagonal boron nitride (h-BN) was incorporated into BiFeO_3 and MnFeO_3 type perovskites by facile impregnation method for the first time and the catalysts presented excellent photocatalytic activity towards various antibiotics and dyes. The characterization tests were carried out by SEM-EDS, TEM, XPS, FTIR, XRD, BET, PL and DRS techniques. The narrower band gap of Type-II heterojunction improved the photodegradation of tetracycline which the reaction rates were calculated as 2.5 times higher than raw perovskites. The outstanding photocatalytic performance of heterojunc-tions was explained by extended excitation wavelength and hindered recombination rate of charge-carriers. In lake and sea water media, 86% and 72% degradation degrees were achieved aver BiFeO_3/h-BN and MnFeO_3/h-BN, respectively, suggesting their practical utilization. BiFeO_3/h-BN and MnFeO_3/h-BN catalysts also exhibited superior catalytic performances for the elimination other contaminants namely, ciprofloxacin, Orange II and Indigo carmine yielding approximately 75% removal at the end of photo-Fenton catalysed reaction. The heterojunctions effectively removed nearly -50% and -70% of ibuprofen from the real pharmaceutical wastewater. The incorporation of hexagonal boron nitride offers an innovative and ideal way to enhance the photocatalytic activity of perovskite catalysts for the elimination of organic pollutants.
查看更多>>摘要：The promising quaternary chalcogenide Cu_2Fe_(1-x)In_xSnS_4 (where x = 0 -0.25 -0.50 -0.75 and 1) thin films were grown using spray pyrolysis technique. The behaviors of indium inclusion on chemical composition, morphological, structural, optical and electrical properties have been investigated using respectively: Energy dispersive X-ray spectrometry (EDX), scanning electron microscopy (SEM), X-ray diffraction (XRD), Maud software, Raman spectroscopy, spectrophotometer and Hall Effect. XRD and Maud software revealed a formation of stannite Cu_2InSnS_4 (x = 1) named CITS from stannite Cu_2FeSnS_4 (x = 0) called CFTS with same preferred orientation (112) plan. Identification of chalcogenide CITS was supported from chemical composition ratio of Cu:In:Sn:S, which are near to theoretical values 2:1:1:4. Electrical resistivity was increased slightly from 5.82 10~(-3) (for CFTS) to 5.94 10~(-3) D.cm (for CITS). This trend may be due to the decrement of crystallite sizes. The energy band gap of CITS was equal to 1.4 eV. These optical and electrical behaviors favorite Cu_2InSnS_4 thin film to be implicate as an absorber material in solar cell applications. Furthermore, this work highlights the surface wettability of Cu_2Fe_(1-x)In_xSnS_4 thin films showing a conversion from hy-drophilic CFTS surface into hydrophobic CITS surface. In addition, photocatalytic activity of Cu_2InSnS_4/SnO_2:F (CITS-FTO) heterojunction has been investigated under Xenon light irradiation using methylene blue (MB) and methyl orange (MO) as representatives pollutant dyes. Moreover, MB dye was continuously degraded during four cycles, meaning that CITS-FTO photocatalyst has relatively good stability in MB degradation. Therefore, this work provides an opportunity for a new successful removal candidate CITS-FTO of water contaminants for photocatalytic applications and new absorber CITS material for photovoltaic applications.
查看更多>>摘要：Strain glass alloys are promising candidates of high performance damping materials for their broad damping peaks. To realize the practical applications, the large damping capacity and broad ambient temperature range are highly desirable. However, the high damping behavior covering ambient temperature has not yet been achieved in strain glass systems, and how to obtain a maximum damping capacity in the same strain glass system remains unclear. Here, we reported the broad ambient temperature damping of Ni_(73-x)Fe_xGa_(27)(x = 23.5-24.5) strain glass alloys. The damping capacity of Ni_(73-x)Fe_xGa_(27) strain glass alloys increases as the compositions move towards the martensite/strain-glass phase boundary, and the maximum damping value (-0.12) is achieved in Ni_(49.5)Fe_(23.5)Ga_(27) strain glass alloy within the phase boundary. The boundaries of martensitic nano-domain are very mobile in phase boundary region, which leads to broad and high damping peak around ambient temperature. Our results provide an effective way to design high performance damping materials.
查看更多>>摘要：To improve the application of transition metal oxides (TMOs) in lithium-ion batteries (LIBs), this study aims to construct electrodes using three strategies, i.e., engineering nano-sized TMOs, introducing different TMOs as hybrid heterostructures, and compositing carbonaceous structures with TMOs. This study presents an efficient procedure to synthesize bimetallic MOFs (Fe@Z67s) as precursors. During the synthesis of MOFs, two key parameters are investigated, i.e., the use of Ar inert gas (O_2-free environment) and the optimization of the iron molar content. After successive carbonization and oxidation, Fe@Z67s are metamorphosed into a hierarchical porous nitrogen-doped carbon (NC) comprising cobalt-based nanoparticles (Co/Co_3O_4/ CoFe_2O_4(CCF)). Under the optimized conditions, the resultant L-CCF/NC-Ar electrode (derived from the synthesized Fe@Z67 under the O_2-free environment (Ar) with a low amount of iron (I)}, discloses the best electrochemical performance as LIB anode. This engineered electrode delivers a remarkable reversible capacity of 1020 mA h g~(-1) after 500 cycles with an excellent capacity retention of 95% at a high current density of 1 A g~(-1). The outstanding electrochemical performance of the developed electrode can be ascribed to the synergistic effect of an optimal ratio of TMOs hybrid/ porous graphitic carbon, hollow nanostructured anode material, high surface area, appropriate N-doping, and the homogeneous distribution of the active sites.
查看更多>>摘要：Highly transparent and submicrometer-grained Yb:Y_2O_3 ceramics were obtained by hot-pressing method with ZrO_2 sintering additive. Hot-pressing method provides extra driving force to promote the densification of Yb:Y_2O_3 transparent ceramics, resulting in high transmittance achieved. The transmittances of all samples were ranging from 80.5% to 81.8% at 1100 nm and 72.7-77.7% at 600 nm. The ceramic samples in this work were sintered at a low temperature of 1600 °C for 3 h, providing dense microstructures with average grain size less than 1 um, which are smaller than those of Yb:Y_2O_3 ceramics prepared by other traditional sintering techniques. The microhardness and fracture toughness were ranging from 8.16 to 7.99 GPa, and from 0.94 to 0.88 MPa-m~(1/2), respectively, which are higher than the comparison samples fabricated by pressureless sintering. The absorption cross-sections of the 1 at% Yb-doped sample at 950 and 976 nm were 0.93 × 10~(-20) and 1.22 × 10~(-20) cm~2, respectively. The fluorescence decay lifetime at 1032 nm was in the range of 0.79-1.36 ms. According to the available literature, this is the first report about Yb:Y_2O_3 transparent ceramics fabricated by hot-pressing sintering without any combined sintering process. The ceramics obtained may have potential use for solid-state lasers partly replacing single crystals.
查看更多>>摘要：Plastic deformation is always inhomogeneous and complicated during hot processing of the superalloy component, making it hard to accurately predict the flow behavior and microstructure evolutions which may deviate greatly from those results obtained during traditional compression tests with a constant strain rate. The hot deformation behavior of a Ni-Cr-Mo based superalloy C276 in shifted strain rate conditions was investigated and a comparison with the constant strain rate compressions was conducted. The flow stress was found to immediately change after varying the strain rate. The strain rate sensitivity (m), which is the exponent of stress change against the strain rate, was calculated to about 0.16-0.24 for C276 superalloy at 1323 K with strain rate in the range of 0.001-1 s~(-1). The strain rate variation affected the microstructure evolution greatly, leading to different dynamic recrystallization (DRX) tendencies from the compressions with a constant strain rate. Shifting the strain rate from high value to low value resulted into a higher extent of DRX in comparison with the reverse process. A cellular automaton (CA) model, considering the evolutions of dislocation density, recrystallization nucleation and grain growth in deformation procedure, was developed to simulate the microstructure evolution and stress response in shifted strain rate compressions. The successful predictions by the CA model showed a good potential application of this approach in understanding the DRX behavior in non-constant hot processing of C276 superalloy.
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Elsevier