查看更多>>摘要：? 2021Novel N-doped carbon coated porous hierarchical MnO microspheres have been successfully synthesized via the simultaneous pyrolysis of MnCO3 and polyacrylonitrile (PAN) at low calcination temperature. The micro/nano structure with uniform N-doped carbon coating, suitable interior pores and tiny primary MnO nanocrystals can significantly increase the electronic conductivity of the composite, reduce the amount of irreversible solid-electrolyte interphase (SEI) layer, accommodate the huge volume change of MnO during cycling and facilitate easier redox reaction of Mn2+/Mnx+ (x>2) to generate extra capacity. By using partially pyrolytic PAN as the conductive agent and binder, the obtained additive-free MnO-based electrode (MnO@NC-S) demonstrates a high reversible capacity of 998 mAh g?1 after 100 cycles at 0.1 A g?1 and remarkable long-term cycling stability with the capacity of 629 mAh g?1 after 500 cycles at 0.5 A g?1.
查看更多>>摘要：? 2021 Acta Materialia Inc.Stacking faults and twins are extremely difficult to form in ceramic materials. At the same time, previous studies often used the metal transition layer to improve the film-substrate bonding force, but ignored its influence on the film structure and mechanical properties. Our research shows that a large number of stacking faults are formed in the Ti transition layer grown on (110) MgO substrate, which induces high density tacking faults in nitride ceramic films with high stacking fault energy, thereby increasing the nanoindentation hardness of the ceramic films. Whether the stacking faults in the Ti transition layer can enter the ceramic films depends on the stacking fault density. This work is of great significance for studying how to induce the formation of stacking faults and twins in ceramics with high stacking fault energy to improve the mechanical properties.
查看更多>>摘要：? 2022 Acta Materialia Inc.In this work, multi strengthening/deformation mechanisms were introduced into a Ni-rich Ni40Co32Cr20Al3.5Ti3Nb1.5 (at%) medium-entropy alloy. After thermo-mechanical procedures, the microstructure is characterized by ultra fine γ' particles (2–18 nm) and short stacking faults. The alloy has superior mechanical properties with gigapascal yield strength, excellent ductility and strong work hardening ability. The initial high strength is caused by the blocking effect of ultra fine γ' particles, dislocation locks (Lomer-Cottrell locks), solute atoms and grain boundaries to dislocation movement. TEM observations at different strains indicate that the increasing number of stacking faults, Lomer-Cottrell locks and deformation twins are the main reasons for the improvement of work hardening ability during deformation. Twinning and dislocation slip, including perfect dislocations and partial dislocations, are the main deformation mechanisms. Our findings show that the coordination of multi strength/toughing mechanisms may be an effect way to enhance the strength-ductility trade-off.
查看更多>>摘要：? 2021The anomalous or bulk photovoltaic (BPV) effect in ferroelectrics is not subject to the Shockley-Queisser limit capping the efficiency of interface-based semiconductor photovoltaics. Therefore, it has been widely explored for applications in photovoltaic energy harvesters, non-destructive read-out mechanisms for data storage, or photorefractive thin-film devices. However, all investigations have so far been restricted to single crystals and epitaxial thin films; there is yet no direct evidence of a bulk photovoltaic charge transport in polycrystalline thin films, which would open a much larger range of economical applications. This study demonstrates the bulk nature of the photovoltaic effect in polycrystalline solution-processed BiFeO3 thin films. A light-polarization-dependent photocurrent is shown. Combined with the dependence of the photocurrent on the poling state of the film and the light intensity, as well as the scaling of open-circuit voltage with electrode distance, this clearly indicates that the charge carrier separation relies on the BPV effect.
查看更多>>摘要：? 2022 Acta Materialia Inc.In this study, an unusual structural distortion in metastable β Ti-Nb was observed after laser melting. Selected area diffraction patterns (SADPs) from transmission electron microscopy (TEM) reveal that after rapid solidification from laser scans in a Ti-25Nb (at.%) sample, a difference in crystal structure was observed between the cellular solidification interior and the intercellular regions. While the intercellular regions remained the bcc (β) phase, the structure of the cell interior dis not match either β or the α’’ martensite. Instead, this structure can be interpreted either as an ordered orthorhombic structure with significantly different lattice parameters compared to α’’, or a distorted β with 8% strain along with one of the <100>β directions with selected variants of nanodomains which originate from the relaxation of interstitial oxygen atoms.
查看更多>>摘要：? 2022 Acta Materialia Inc.Sodium-ion batteries have attracted tremendously significant attention as an alternative to Li-ion batteries due to the similar electrochemical properties. However, owing to the larger atomic radius of sodium, the sodium-ion batteries have been inevitably suffered from the inferior electrochemical reaction kinetics and descending cyclic stability, limiting its practical applications. Here, sodium-ion batteries based on 3D 1T-SnS2/RGO composite electrode with highly reversible sodiation/desodiation process are realized through a facile CVD process and spray coating. It displays excellent initial specific charge and discharge capacities (766.7 mAh g?1 and 768.8 mAh g?1), after 100th cycle, the charge and discharge capacities are 648.1 mAh g?1 and 650.8 mAh g?1, respectively, with 84.6% capacities retention ratio, indicating the excellent reversibility and high electrochemical reaction kinetics. The composite sodium-ion battery anode still delivers high specific capacities of 865.6 mAh g?1, 758.2 mAh g?1, 678.5 mAh g?1, 581.2 mAh g?1 and 503.8 mAh g?1 at the current density of 0.1 C, 0.5 C, 1 C, 2 C and 5 C, respectively, indicating its excellent reversible sodiation/desodiation reaction and rate capability. This work confirms the high potential of the SnS2-based anode for SIBs from its highly reversible capacity and excellent rate capability and points out the significance of the rational design of three-dimensional composite anode with high reversibility and electrochemical reaction kinetics.
查看更多>>摘要：? 2022Unique nanorod precipitates with a core-shell structure are found to nucleate from the grain boundaries of a bulk nanocrystalline Al-Ni-Y alloy fabricated via powder consolidation, contributing significantly to stabilization and strengthening. The local structure, chemistry, and evolution of these features during annealing are reported here. In the as-consolidated state, the nanorods can be either structurally ordered or disordered, yet a consistent chemical patterning is found where the core is primarily Al plus C while the shell is enriched with Y. As annealing time increases, more nanorods transform to an ordered structure as they coarsen while the core composition remains unchanged. In contrast, the shell chemistry transitions from Y-rich to Ni-rich with longer annealing treatments, most likely due to the different diffusivities of Y and Ni in Al. Moreover, a spatial and chemical correlation between the nanorods and amorphous complexions is observed, suggesting that these complexions serve as preferential nucleation sites.
查看更多>>摘要：? 2022 The AuthorsBauschinger test in uniaxial tension-compression mode was carried out for the first time on the pure Al specimens having homogeneous ultra-fine grained (UFG) microstructures fabricated by equal-channel angular pressing (ECAP) and subsequent annealing processes. Significant Bauschinger stress (transient softening), Bauschinger energy parameter and their strong dependences on the tensile plastic pre-strain at the very early stage of the tensile deformation were measured in the UFG specimens, in sharp contrast to their coarse-grained (CG) counterpart. The grain size dependence of the Bauschinger effect in pure Al was qualitatively discussed in terms of the back stress arising from the formation of dislocation pile-up against the grain boundary during plastic deformation.
查看更多>>摘要：? 2022The appearance of serrated flow on stress-strain curves in single-phase high entropy alloys (HEAs) suggests that their lattices are arranged and behave differently than those in pure metals. In this study, a micromechanical model linking serration amplitude and solute concentration difference at the dislocation line was built to quantify the concentration of “mysterious solute” in HEAs. Using the model, the concentration of “mysterious solute” in a model HEA, CoCrFeNi, was determined to be ～34 at.%. Despite that certain facets of the physical nature of the solute remains to be further delved into, our present findings indeed suggest a quantitative distinction between the solvent and solute in single-phase HEAs. As opposed to commonly treating these concentrated solid solutions as an average “medium”, our work paves the avenue of separating out the solute and solvent, which is beneficial to unveiling many key questions in HEAs (e.g., obstruction of the solute to dislocation motion).
查看更多>>摘要：? 2022 Acta Materialia Inc.Because Cu is an austenite γ stabilizer, it is thought that Cu only dissolves in the FCC γ phase but not in the BCC δ when Cu-containing PHSS are treated in a dual δ-γ solid solution at high temperature. However, the nano precipitation of Cu in the allotriomorphic δ found upon quenching from 1295°C. To study this unexpected phenomenon, thermodynamic calculations were performed. The predicted solubilities of Cu in the γ and δ at 1295°C were 3.52 and 1.99 wt%. Consequently, quenching the solid solution from 1295 to 25°C results in the ultra-supersaturation of Cu in the δ. The vacancy concentration in the δ solution was estimated to change from 1024 vac./m3 at 1295°C to105 vac./m3 at 25°C; quenching yields excess vacancies. Thus, Cu-rich nanoparticles precipitate in the δ matrix through the interdiffusion of the ultra-supersaturated Cu and excess vacancies.
NSTL
Elsevier