查看更多>>摘要：Fe-Cr-Al alloys,owing to their absence of allotropic transformation,require multiple cycles of rolling and recrystallization annealing processes to achieve substantial grain refinement,ultimately leading to the attainment of outstanding mechanical properties.However,the corresponding manufacturing costs will also increase greatly.In this work,we have proposed a new microstructural preparation process.Sim-ply using warm rolling for an ultra-coarse-grained Fe-Cr-Al alloy to introduce lamellar kink bands(KBs)into the matrix,the mechanical properties can be significantly improved.By using electron backscatter diffraction(EBSD)and transmission electron microscopy(TEM),and combined with Schmid factor(SF)calculation,the formation mechanism of KBs has been revealed.When the slip plane and direction are nearly perpendicular to the loading force direction(LFD)during the continuous grain rotation,the dislo-cation wall will evolve into the KBs boundaries.Simultaneously,a huge orientation separation between the matrix and KBs will be produced.As strain continues to rise,KBs undergo a transformation,tran-sitioning from low-angle-grain boundaries(LAGBs)to high-angle-grain boundaries(HAGBs),occasionally adopting a configuration as coincident site lattice(CSL)boundaries with reduced interface energy.Re-sults of the tensile test,cyclic loading-unloading-reloading tensile test,and the strengthening calculation show that KBs can pronouncedly enhance the strength by their heterogeneous refinement on the original grains and hetero-deformation induced(HDI)strengthening effect from the dislocation density discrep-ancy between the matrix and internal KBs,the grains containing KBs(KBGs)and the grains without KBs(or KBs-free-grains,KFGs).The theoretical calculation value of the strengthening contribution from KBs on yield strength can be up to 225.5 MPa,with a minimum value exceeding 153 MPa.On the other hand,the ductility can be retained to some extent through stimulating the KBs boundary delamination mecha-nism.The present study provides a low-cost and feasible processing method for fabricating Fe-Cr-Al alloy with high strength and good ductility.
查看更多>>摘要：The poor corrosion resistance restricts the industrial applications of nanocrystalline soft magnetic Fe-Zr-B alloys.We reported a facile plasma-nitriding surface process to enhance the corrosion resistance of a nanocrystalline Fe90Zr7B3 alloy without deteriorating its soft magnetic properties.Potentiodynamic po-larization and electrochemical impedance spectroscopy were performed to investigate the corrosion be-havior.The nitrided alloy shows higher corrosion resistance than the untreated alloy,as evidenced by a nobler corrosion potential,lower corrosion current and higher polarization resistance of surface corrosion film,while their magnetic properties are similar.The microstructures of both nanocrystalline alloys were examined by high-resolution transmission electron microscopy(HRTEM)and the compositions of their corrosion films analyzed by X-ray photoelectron spectroscopy(XPS).For the nitrided alloy,a more homo-geneous nanocrystalline structure developed in the surface nitrided layer containing corrosion-resistant nitride phases(Fe3N and ZrN)provides a higher resistance against chloride corrosion.Moreover,the ni-trided layer facilitates the formation of a more protective corrosion film with the increased ratios of Fe2+/Fe3+and O2-/OH-as well as higher enrichment of Zr-and B-oxides,while the N-species(NH4+and NO3-)formed in the corrosion film behave as good corrosion inhibitors and further enhance the film pro-tection.Our findings provide a simple strategy for the preparation of corrosion-resistant nanocrystalline soft magnetic alloys to satisfy a variety of engineering requirements.
查看更多>>摘要：The intelligent era brings electronics closer to humans,but also produces a large scale of electromag-netic(EM)radiation simultaneously,which causes serious harm to health and high sophisticated equip-ment.Exploring the underlying response logic of EM materials is urgently needed to face the challenge of EM interference(EMI)and secondary EM pollution better.Herein,PEDOT:PSS-patched magnetic graphene films are fabricated by vacuum-assisted molecular patching engineering,with tunable EM wave response.Based on the observation of micro-nano structure,the dielectric genes are visually revealed,which offers a bran-new horizon for the optimization of EM properties.Impressively,the constructed films achieve double band shielding toward gigahertz wave and infrared radiation.The optimal EMI shielding efficiency exceeds 99％,and covers the entire X-band.Meanwhile,the green shielding index rises from 0.3 to 0.6,indicating that it is a potential green EMI shielding materials.Furthermore,the periodic macroscopic interfaces and the inherent thermal anisotropy endow the films with thermal insulation and flexible in-frared stealth functions in simulated thermal environments.This work refreshes the insight into multi-band shielding,providing a new idea to EM energy governance.
查看更多>>摘要：The assistance of alloying elements provides enormous opportunities for the discovery of high-performance face-centered cubic(FCC)medium-entropy alloys(MEAs).In this work,the influence of al-loying element Mo on the phase stability,stacking fault energy(SFE),deformation mechanisms,lattice distortion,and mechanical properties of(CoCrNi)100-xMox(0 ≤ x ≤ 10)MEAs was synthetically explored with the first-principles calculations.It indicates that the FCC phase remains metastable at 0 K,and its stability degenerates with increasing Mo content.The monotonous decrease of SFE is revealed with the rise of Mo content,which promotes the activation of stacking faults,deformation twinning,or martensitic transformation.Raising Mo content also causes the aggravation of lattice distortion and thus triggers in-tense solid solution strengthening.Significantly,the essential criterion for the composition design of FCC(CoCrNi)100-xMo MEAs with superior strength-ductility combination was established based on the syner-gistic effects between multiple deformation mechanisms and solid solution strengthening.According to the criterion,the optimal composition is predetermined as(CoCrNi)93Mo7 MEA.The criterion is proved to be effective,and it can provide valuable inspiration for the development of alloying-element reinforced FCC multi-principal element alloys.
查看更多>>摘要：Bone-mimicking gradient porous NiTi shape memory alloys(SMAs)are promising for orthopedic im-plants due to their distinctive superelastic functional properties.However,premature plastic deformation in weak areas such as thinner struts,nodes,and sharp corners severely deteriorates the superelasticity of gradient porous NiTi SMAs.In this work,we prepared gradient porous NiTi SMAs with a porosity of 50％by additive manufacturing(AM)and achieved a remarkable improvement of superelasticity by a simple solution treatment regime.After solution treatment,phase transformation temperatures dropped signif-icantly,the dislocation density decreased,and partial intergranular Ti-rich precipitates were transferred into the grain.Compared to as-built samples,the strain recovery rate of solution-treated samples was nearly doubled at a pre-strain of 6％(up to 90％),and all obtained a stable recoverable strain of more than 4％.The remarkable superelasticity improvement was attributed to lower phase transformation tem-peratures,fewer dislocations,and the synergistic strengthening effect of intragranular multi-scale Ti-Ni precipitates.Notably,the gradient porous structure played a non-negligible role in both superelasticity deterioration and improvement.The microstructure evolution of the solution-treated central strut after constant 10 cycles and the origin of the stable superelastic response of gradient porous NiTi SMAs were revealed.This work provides an accessible strategy for improving the superelastic performance of gra-dient porous NiTi SMAs and proposes a key strategy for achieving such high-performance architectured materials.
查看更多>>摘要：The oxidation and interdiffusion behavior of a novel AlCoCrFeNiY bond coat deposited on a directionally solidified Ni-based superalloy were systematically studied at 1050,1100 and 1150 ℃,and compared with a conventional NiCoCrAlY coating deposited on the same substrate.The AlCoCrFeNiY bond coat exhibits lower oxide growth rates due to its large columnar grains and low Al activity at the oxide scale/bond coat interface.Meanwhile,AlCoCrFeNiY has higher resistance to oxide spallation than NiCoCrAlY,which is attributed to the formation of a clean and defect-free metal/oxide interface.Significant interdiffusion occurs across the AlCoCrFeNiY/superalloy substrate interface.Our experimental evidence and thermody-namic modelling suggest that Fe accelerates interdiffusion and destabilizes the γ'phase,thereby causing the formation of a thick and γ'-depleted interdiffusion zone.In addition,the AlCoCrFeNiY bond coat un-dergoes more Al depletion and subsequent β to γ transformation compared with NiCoCrAlY.Based on the findings in this work,a novel AlCoCrFeNiY/NiCoCrAlY double-layer bond coat was designed,tested and validated to achieve optimal balance between oxidation and interdiffusion.
查看更多>>摘要：An Al2O3 dispersion strengthened(ADS)alloy with an ultra-high softening temperature of～1200 K was fabricated by the in-situ internal oxidation and reduction methods.The evolution of the nanometer Al2O3 particles,grain size,and consequently the softening behavior of this ADS alloy,were investigated by con-ducting the annealing treatments in the range from 673 K to 1273 K for 60 min.These refined nanometer Al2O3 particles were found to be highly stable at elevated temperatures,leading to the high dislocation density and grain boundary stability of the matrix.The average grain size was found to increase extremely slowly from～0.60 μm to～0.74 μm with increasing annealing temperatures from 773 K to 1273 K.A cri-terion for grain boundaries migration and softening was established based on the competition between grain growth and pinning effect of Al2O3 particles.The strong pinning effect of Al2O3 particles was found when the grain size was between the lower limit(about 0.4-0.5 µm)and upper limit(2.18 µm).The occurrence of softening behavior was attributed to the rapid increase of the proportion of grains larger than the upper limit.A modified Hall-Petch relationship was established by introducing the integration of the grain size distribution,which can describe this correlation between softening behavior and the pinning effect of Al2O3 particles.The current study not only sheds light on the further understanding of the softening mechanism of ADS copper alloy but also provides a useful route for designing copper alloy with high softening resistance.
查看更多>>摘要：The creep anisotropy of Ni-based single crystal superalloys was studied at 750 ℃/750 MPa.Transmission electron microscopy(TEM)observations showed that stacking faults and micro-twins were the typical dislocation configurations,which all originated from the activity of {111}<112>slip systems.Then,the orientation rotation caused by the activity of the main {111}<112>slip system would accelerate the spec-imen fracturing in shear fracture mode.Furthermore,the orientation rotation would dominate the creep anisotropy.The orientation rotation would occur during the entire creep process,the greater the degree of rotation,the more severe the asynchrony of rotation,which would result in nonuniform deformation and local stress concentration,and exacerbate the failure of the specimen.
查看更多>>摘要：The polymer-based solid-state electrolytes(PSEs)are promising for solid-state batteries but they have deficiencies such as low ionic conductivity,low lithium-ion transference number,and unstable elec-trode/electrolyte interface.Herein,we designed a hydroxyapatite nanowire doped with high-valence cations in anticipation of the formation of positively charged active sites on the nanowire surface.The higher surface activity can reduce the reaction activation energy on the nanowire surface and adsorb the anions in the PSEs as a way to improve the ionic conductivity and Li+transference number of the PSEs.The active sites on the surface of the nanowires anchor the anions,thus increasing the Li+transfer-ence number to 0.38,which effectively improves the ionic conductivity of the PSE to 1.58 × 10-4 S cm-1 at room temperature.At the same time,the composite polymer electrolyte has a wide electrochemical window.The lithium symmetric cell stably cycles for 800 h at a current density of 0.1 mA cm-2,and the LiFePO4||Li full cell steadily cycles for 180 cycles at a rate of 0.5 C with a capacity retention of 94.2％.The ion doping strategy to change the surface electrical behavior of nanowires provides an idea to improve the ionic conductivity of solid-state electrolytes.
查看更多>>摘要：Lithium-sulfur(Li-S)batteries are considered appealing power sources due to their high theoretical en-ergy density(2600 Wh kg-1),low cost,and environmental friendliness.However,their widespread ap-plicability is restricted by two scientific problems:sluggish sulfur reaction kinetics and severe polysul-fide shuttle effects.Multifarious strategies have been developed to overcome these two obstacles and achieve high sulfur utilization and capacity retention.Among these strategies,the introduction of cat-alytic materials into the Li-S battery system can greatly accelerate sulfur conversion and effectively in-hibit the polysulfide shuttle effects.Herein,we have comprehensively reviewed the recent progress of catalytic engineering for polysulfide conversion in high-performance lithium-sulfur batteries.First,various catalytic materials serve as sulfur hosts,functionalized separators,and electrolyte additives;the mecha-nisms by which these materials promote the conversion of polysulfides in Li-S batteries have been sys-tematically summarized.The relationship of structure,preparation,property,advantages,and limitations of these catalytic materials are comprehensively presented.Subsequently,the advanced characterization techniques of these catalytic processes are discussed,shedding light on the fundamental understanding of catalytic effects for improved electrochemical performance.Furthermore,future design tactics for high-performance Li-S batteries are discussed.
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