查看更多>>摘要：The fatigue damage behavior of the nanocrystalline Au films on polyimide substrates was investigated.It was found that the very high-cycle fatigue damage resistance of the Au film was significantly enhanced by at least a factor of ～2 in supported loading through adding an ultrathin Ti interlayer at the Au film/polyimide interface.Such a better fatigue damage resistance is mainly ascribed to the effective suppression of voiding at the Au film/polyimide interface through modulation of the Au/Ti interface,and thus the propensity of the cyclic strain localization and grain boundary cracking is reduced.The finding may provide a potential strategy for the design of flexible devices with ultra-long fatigue life.
查看更多>>摘要：TMSi2 (TM =Ta,Mo) are extensively used as thermal emissivity agents in high emission coatings due to their well-known "high" emissivity in infrared range.However,there is a paucity of the high temper-ature (HT) emissivity property of these two silicides.Moreover,room temperature (RT) spectrometer measurements have demonstrated that the emittance in infrared range of two silicides was considerably low.Therefore,providing critical HT data and satisfactory elucidation on the emission incompatibility of TMSi2 is eagerly needed.In this contribution,combining first principles calculations and Drude model,the reflectance spectra of TMSi2 were predicted at both RT and HT.Consistent with spectrometer mea-surements,the intrinsic emittance of silicides was relatively low in the entire investigated temperatures.To explain the incompatible emission behavior,two simplified models including the majority of high emissivity coating,SiO2,were proposed.Intriguingly,with SiO2 considered in simulations,no matter covered on the surface or blended in the composites,the emittance of the TMSi2 enhanced significantly.Our theoretical results demonstrate the non-negligible significance of oxides on the high temperature performance of silicides and provide the guidelines for improving the emission performance of silicides and searching for potential high emissivity agents.
查看更多>>摘要：The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood thus far.Here,we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms,which result in an excel-lent low-temperature toughness of the steel.Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically,especially at low-temperatures.Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects,which produce large quantities of deformation twins,εhcp-martensite and α'bcc-martensite.Inversely,in the fine-grained steels,the formation of deformation twins and martensite is significantly inhibited,leading to the decrease of impact toughness.Microstructural characterizations also indicate that εhcp-martensite becomes more stable than α'bcc-martensite with decreasing temperature,resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature.In the coarse-grained samples under impact deformation at-80 C,εhcp-martensite transformation,α'bcc-martensite transformation and deformation twinning all occur simultaneously,which greatly improves the toughness of the steel.
查看更多>>摘要：Oxide inclusions widely exist in additively manufactured components due to the native oxide layer on the powder surface,together with gas impurities during the printing process.Using in-situ tensile tests combined with electron backscatter diffraction (EBSD) and electron channeling contrast imaging (ECCI)techniques,we propose an asymmetrical cracking mechanism around the oxide inclusions in a selec-tive laser melted 316L stainless steel.The heterogeneous sub-micro cellular structures lead to different twinning tendencies around the inclusions due to the size-related critical twinning stresses,and the deformation-induced nano-twin clusters can resist the cracking propagation,therefore resulting in the asymmetrical cracking behaviors around the inclusions.
Min ZhaHong-Min ZhangXiang-Tao MengHai-Long Jia...
141-149页
查看更多>>摘要：Single-phase Al-Mg alloys processed by severe plastic deformation (SPD) usually suffer from unsatis-factory thermal stability at moderate to high temperatures with recrystallization occurring and obvious grain coarsening.In the present work,an Al-7Mg alloy prepared by equal-channel angular pressing(ECAP) possessed markedly enhanced thermal stability upon annealing at moderate to high temperatures(200-275 ℃),compared with those ultrafine-grained dilute Al-Mg alloys with a uniform microstructure.The enhanced thermal stability is due primarily to the multimodal grain structure consisting of nano-,ultrafine-and micron-sized grains,strong segregation and/or clusters of Mg solute along grain bound-aries (GBs),and Al3Mg2 precipitates formed during annealing.First,extensive recovery predominates over recrystallization and consumes most of the stored energy in the ECAPed Al-7Mg alloy annealed at≤ 275 ℃,leading to the recrystallization and growth of nano/ultrafine grains being retarded or post-poned.Moreover,Mg solute segregation and/or clusters along GBs of nano/ultrafine grains could further suppress grain growth via diminishing GB energy and dragging GBs efficiently.In addition,Al3Mg2 pre-cipitates formed with increasing annealing time could inhibit grain growth by pinning GBs.The present multimodal-grained Al-7Mg alloy with enhanced thermal stability is believed to be particularly attractive in potential engineering applications at moderate to high temperatures.
查看更多>>摘要：Tungsten bronze coatings and films have attracted global attention for their applications in near-infrared(NIR)-shielding windows.However,they are unstable in strong ultraviolet,humid heat,alkaline and/or oxidizing environments and are difficult to be coated on glass surfaces with complex shape.Here,we address these limitations by doping sodium tungsten bronze (NaxWO3) into bulk glasses using a simple glass melting method.X-ray diffraction,Raman spectroscopy,X-ray photoelectron spectroscopy,TEM and SEM-EDS characterization confirmed the presence of sodium tungsten bronze (NaxWO3) functional units inside the 34SiO2-38B2O3-28NaF glass matrix.Because the functional units are well protected by the glass matrix,the fabricated glasses are stable under hot,humid,oxidizing conditions,as well as under ambient conditions,with no change after 360 days.The NIR-shielding performance of these glasses can be adjusted to as high as 100 ％ by varying WOx concentration (2-8 mol％) and quenching temperature (1000-1400℃).With a content of 6 mol％ WOx and a quenching temperature of 1000 C,the bulk glass shows 63％ transmission of visible light and only 11％ transmission of NIR light at 1100 nm.Thermal insulation experiments show that the NIR-shielding performance of the glasses are far superior to commercial soda lime window glass or indium-doped tin oxide (ITO) glass,and comparable to cesium tungsten bronze coated glass.The novel bulk glasses have higher stability,simpler processing,and can be easily made into complex shapes,making them excellent alternative materials for energy-saving glasses.
查看更多>>摘要：The correlation between depassivation and repassivation processes,which is significant in erosion-corrosion,was quantitatively investigated by single particle impingement tests at various flow velocities and impact angles.The results show that both repassivation and depassivation processes are associated with the kinetic energy of solid particle,and demonstrate that the repassivation is retarded by depas-sivation.This phenomenon probably results from the depassivation-induced microstructure evolution.On this basis,the dependence of critical flow velocity (CFV) for erosion-corrosion on the solid particle concentration and diameter is further theoretically predicted and experimentally verified.Accordingly,the crucial role of depassivation-repassivation in CFV phenomenon is further highlighted.
查看更多>>摘要：The extended cycle life of cells is often sacrificed at the expense of high specific energy for high-nickel materials.Cation doping is a promising method to build high-nickel cathode with high energy density and long cycle life.Herein,a trace amount of Mg-B co-doping in LiNi0.6Mn02Co0.2O2 (NMC622) is investigated in this work,which shows improved structural and electrochemical stability of 1％ Mg-0.5 ％ B co-doped material at both 30 and 55 ℃ in coin-cell.Comprehensive chemical composition,structural,and surface analysis are carried out in this paper.It was found that all the selected materials have a similar compo-sition to the target.Moreover,Mg and B doping have different effects on the crystal structural change of NMC622,to be more specific,the c-lattice parameter increases with Mg doping,while the Li+/Ni2+mixing content increases when B was incorporated into the lattice.Furthermore,the microstructure of primary particles was changed by B doping significantly as confirmed by the SEM images.There were marginal benefits in terms of structural and electrochemical stability of materials introduced by Mg or B sole doping.In comparison,incorporating a suitable amount of both Mg and B into NMC622,we found the capacity retention of cells was noticeably improved by reducing the impedance growth and preventing cation mixing during cycling.This study demonstrates the importance of co-incorporation of Mg,B,and optimizing the co-dopant content to stabilize NMC622 as cathode for lithium-ion batteries.
查看更多>>摘要：Femtosecond laser induced periodic surface structures (LIPSSs) are excellent biomimetic iridescent antireflective interfaces.In this work,we demonstrate the feasibility to develop tunable iridescent antire-flective surfaces via simultaneous synthesis of functional metal-oxide nanomaterials,in situ deposition and hierarchical LIPSSs nanostructuring by means of femtosecond laser ablation (fs-LA) of tungsten (W)and molybdenum (Mo) in air.Adjusting the scanning interval from 1 μm to 20 μm allows the mod-ulation of particle deposition rates on LIPSSs.Diminishing the scan interval enables a higher particle deposition rate,which facilitates the development of better UV-to-MIR ultrabroadband antireflective surfaces with a less pronounced iridescence.Through comparing the reflectance of hierarchical LIPSSs with different densities of loosely/tightly deposited particles,it is found that the deposited WOx and MoOx particle aggregates have high UV-to-MIR ultrabroadband absorbance,especially extraordinary in the MIR range.Loosely deposited particles which self-assembly into macroporous structures outper-form tightly deposited particles for ultrabroadband antireflective applications.The presence of loosely deposited MoOx and WOx particle absorbers can cause up to 80 ％ and 60 ％ enhancement of antire-flectance performances as compared to the tightly particle deposited LIPSSs samples.One stone of"fs-LA technique" with three birds of (particle generation,in situ deposition and LIPSS hierarchical nanostruc-turing) presented in this work opens up new opportunities to tune the reflectance and iridescence of metallic surfaces.
查看更多>>摘要：The NiSiAlY material is a promising candidate to replace NiCrAlY,which can withstand the harsh salt-spray conditions in marine environment.To efficiently design novel NiSiAlY alloys,this work establishes a thermodynamic dataset of the Al-Ni-Si-Y quaternary system using the CALPHAD (CALculation of PHAse Diagrams) approach.We employ this database to calculate and predict the phase constitutions and solid-ification behaviors of different NiSiAlY alloys concerning the content variations of Al and Si.We have further proposed the selection of the NiSiAlY alloys for serving in marine salt-spray environment with three constraints:(i) outstanding mechanical property;(ii) good high-temperature anti-oxidation;(iii)excellent corrosion resistance.This results in a compositional range of the NiSiAlY alloys with 1 wt％＜ w(Si) ＜ 5 wt％,11 wt％ ＜ w(Al) ＜ 20 wt％ and w(Y) =1 wt％,which corresponds the L12+bcc_B2+Ni5Y ternary phase region at temperatures ranging from ～500 to ～1000 ℃.Our predictions are validated by key experiments,suggesting that the model-based description of the Al-Ni-Si-Y system can serve as a guidance to design the novel NiSiAlY alloys in resisting harsh salt-spray environment.
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