查看更多>>摘要：In this work,Cf/(CrZrHfNbTa)C-SiC high-entropy ceramic matrix composites with good load-bearing,elec-tromagnetic shielding and ablation resistance were designed and reported for the first time.The compos-ites were fabricated by an efficient combined processing of slurry infiltration lamination(SIL)and precur-sor infiltration and pyrolysis(PIP).Density and porosity of the as-fabricated composites are 2.72 g/cm3 and 12.44 vol.％,respectively,and the flexural strength is 185±13 MPa.Due to the carbon fiber rein-forcement with high conductivity and strong reflection,and high-entropy(CrZrHfNbTa)C ceramic matrix with strong absorbability,the total Electromagnetic interference shielding efficiency(SET)of the compos-ites with a thickness of 3 mm are as high as 88.2 dB and 90 dB respectively in X-band and Ku-band.This means that higher than 99.999999％electromagnetic shielding is achieved at 8-18 GHz,showing excel-lent electromagnetic shielding performance.The Cf/(CrZrHfNbTa)C-SiC composites also present excellent ablation resistance,with the linear and mass ablation rates of 0.9 μm/s and 1.82 mg/s after ablation at the heat flux of 5 MW/m2 for 300 s(～2450 ℃).This work opens a new insight for the synergistic de-sign of structural and functional integrated materials with load-bearing,electromagnetic shielding and ablation resistance,etc.
查看更多>>摘要：In this work,the coatings used phosphorylated chitosan(PCS)and GP-108 via the dip-coating method presented exceptional flame retardancy and antibacterial properties for flexible polyurethane foams(FPUF).PCS/GP@FPUF with 35％weight gain of PCS/GP can receive the UL-94 V-0 rating and obtain a 32％reduction of peak heat release rate value compared with that of FPUF,and it remains relatively dense char residues.The effective heat of combustion of PCS/GP@FPUF is 21.6 kJ/g,presenting a 22％decrease compared with that of FPUF.Meanwhile,the PCS/GP coatings mainly have the condensed-phase flame-retardant mechanism associated with the analysis of char residues and the volatile products released through the thermal degradation process.X-ray photoelectron spectroscopy results confirm that the char residues of PCS/GP@FPUF consist of highly-graphitized carbon and it formed P-N-Si synergistic char lay-ers.In addition,the antibacterial rates of PCS/GP@FPUF against Escherichia coli(E.coli)and Staphylococcus aureus(S.aureus)are 99.99％,and the incorporation of GP-108 does not influence the antibacterial proper-ties of PCS.Importantly,the resiliency of FPUFs has been slightly influenced.Briefly,the flame-retardant and antibacterial FPUFs with wonderful resiliency are hopeful to be applied as filler materials for vehicle seats and obtain longer service lives.
查看更多>>摘要：Mo has been widely reported as a conducive element for the corrosion resistance of massive alloy sys-tems.However,the mechanism of Mo optimizing the corrosion resistance is complicated,and in-depth studies are still required.The present work comprehensively and quantitatively studied the critical influ-ences of Mo on the passivation and repassivation behavior of CoCrFeNi HEA based on the dissolution-diffusion-deposition model proposed in our previous work.The experimental results indicated that Mo remarkably eliminated the metastable pitting corrosion,significantly improved the breakdown potential and perfectly protected the CoCrFeNiMo0.2 HEA from pitting corrosion.The modelling and X-ray photo-electron spectroscopy(XPS)results both show that in the passivation process,MoO2 was the last product to deposit,thereby existing in the outer layer of the passive film.Mo addition increased the Cr content by weakening the deposition of Fe2O3 and Fe3O4 and also improved the Cr2O3/Cr(OH)3 ratio by promot-ing deprotonation of Cr(OH)3,thus enhancing the quality of passive film.Besides,when pitting corrosion occurred,MoO2,MoO3,and FeMoO4 were the first products to deposit and accelerated the repassivation process of HEA by timely covering the matrix in the pit cavity,thereby preventing further corrosion of the matrix.
查看更多>>摘要：Hydrogen embrittlement,also known as hydrogen-induced cracking,is a longstanding concern for zirco-nium(Zr)and its alloys.The affinity for hydrogen in zirconium results in the formation of brittle hydrides.Hydrides are conventionally thought to facilitate crack propagation,and the prevailing recommendation to hinder hydride embrittlement involves reducing the hydrogen concentration in the material and ap-plying slow cooling to reduce thermal stresses.Here,in Zr with a maximum hydrogen concentration of 43 wppm,we show that cracks initiate unexpectedly after annealing,a step that involves slow cooling and no external stress.With a suite of high-resolution microscopy,we show that annealing cracks initiate at prismatic δ-hydrides,whose presence is unexpected.The microscopic annealing crack paths are conse-quently crystallographic,following the habit plane of these prismatic δ-hydrides.The commonly reportedγ-hydride and δ-hydrides that develop on the basal plane are found not to initiate cracks.We rationalize that prismatic δ hydrides result from the intergranular thermal residual stresses that develop during slow cooling.This finding of uncommon annealing cracking further advances the mechanistic understanding of hydride embrittlement in zirconium and can lead to new strategies for design and fabrication of advanced zirconium alloys for harsh environments.
查看更多>>摘要：The high-strength and creep-resistant Mg-Al-Ca-Mn alloys have broad application prospects.However,solidification cracking occurs in these alloys in certain conditions and the origin is still unclear.This work investigated the relationship between the solidification path,microstructure evolution and solidification cracking behavior of the Mg-xAl-2Ca-Mn alloys during tungsten inert gas(TIG)welding.Results show that when the fusion zone's Ca/Al mass ratio ranges from 0.4 to 1.64,solidification cracking occurs at a Ca/Al mass ratio of～0.7.As the Ca/Al mass ratio approaches this value,the grain size increases,and the Laves phases are reduced gradually.The early formed Laves phases play an important role in promoting dendrite segmentation,refining grain size and enhancing grain boundaries.When a solidification path delays the formation of Laves phases,the Laves phases will be reduced accompanied by grain coarsening.In such a solidifying microstructure,intergranular cavitation is easy to occur,and the resistance of the semi-solid alloy to crack propagation is severely reduced.
查看更多>>摘要：A bonding approach based on laser surface modification was developed to address the poor bonding be-tween Si3N4 ceramic and Cu.The bonding mechanism in Si3N4/Cu heterogeneous composite structure fabricated by laser modification-assisted bonding is examined by means of scanning/transmission elec-tron microscopy and thermodynamic analysis.In the bonding process under laser modification,atomic intermixing at the interface is confirmed,as a result of the enhanced diffusion assisted by the dissocia-tion of Si3N4 ceramic by laser.The dissociating Si precipitations on the surface,as well as the formation of micro-pores interfacial structure,would be the key concept of the bonding,by which the seamless and robust heterointerfaces were created.By controlling the laser-modifying conditions,we can obtain a reli-able heterostructure via the optimization of the trade-off of the surface structure and bonding strength,as determined by the laser-modified surface prior to bonding.The maximum structure depth and S ratio at the Si3N4 surface were produced at a laser power of 56 W,corresponding to the maximal shear strength of 15.26 MPa.It is believed that the further development of this bonding technology will advance power electronic substrate fabrication applied in high-power devices.
查看更多>>摘要：High-density carbon/carbon(C/C)composite plays a critical role in the aerospace industry owing to excellent mechanical properties and resistance to ablation.However,traditional manufacturing relies on pitch precursor and hot isostatic pressure impregnation and carbonization(HIPIC)technology,which is time-consuming and expensive.In this study,we report an innovative method utilizing polyarylacetylene(PAA)resin and ultra-high pressure impregnation and carbonization(UHPIC)technology.The extremely high char yield of PAA resin(85 wt.％)and high isotropic pressure of UHPIC(over 200 MPa)promote the densification of the composite.As a result,we achieve a high-density(1.90 g/cm3)C/C composite with a high degree of graphitization(81％).This composite exhibits impressive properties,including flexural strength of 146 MPa,compressive strength of 187 MPa,and thermal conductivity of 147 W/(m K).When exposed to oxyacetylene flame at 3000 K for 100 s,it displays minimal linear ablation,with a rate of 1.27×10-2 mm/s.This study demonstrates the exceptional graphitizable characteristic of PAA resin,setting it apart from conventional resins.Our time-saving and cost-effective approach holds significant promise for aerospace applications,particularly in harsh aerodynamic heating environments.
查看更多>>摘要：Z-scheme heterojunction is an effective strategy in photocatalysis,when hetero-interfacial intimate con-tact is the center of high-performance Z-scheme heterojunction structure.Here,x-MoS2[x=plate(p),flower(f),and solid sphere(s)]with extensive optical absorption and high conductivity and stable UiO-66-NH2(y)(y=100,300,and 500 nm)with rich Lewis's acid sites were integrated to a series of x-MoS2@UiO-66-NH2(y)Z-scheme heterojunctions,which were fully characterized and used for photocat-alytic reduction of CO2(pCO2RR)into CH4 and CO.In response to the difficult modification of MoS2 and loose contact of composite bulk materials,the micro-geometric configurations on the size of UiO-66-NH2 and the morphology of MoS2 were optimized to achieve an.intimate contact.The Z-scheme heterojunc-tion f-MoS2@UiO-66-NH2(100 nm)with perfectly matched micro-geometric configuration exhibited an excellent electron consumption rate(Rele)of 263.78 μmol g-1 h-1 and a high CH4 yield of 27.18 μmol g-1 h-1 with a selectivity of 82.44％,being far superior to most MoS2-and MOFs-based heterojunctions.Com-prehensive investigations with extensive photoelectric characterizations,control experiments,and den-sity functional theory(DFT)calculations demonstrate that the excellent photocatalytic performance of f-MoS2@UiO-66-NH2(100 nm)could be attributed to that(ⅰ)the low size of UiO-66-NH2 strengthens mutual alignment and increases outer surface to maximize heterointerface contact with MoS2,acceler-ating the interfacial charge transfer;(ⅱ)the hierarchical structure of f-MoS2 with optimal basal plane curvature greatly reduces contact barriers to present a high charge throughput with a charge excita-tion rate of 1.967 mV,smooth initiating the 8-electron CO2 methanation.Additionally,the durability of f-MoS2@UiO-66-NH2(100 nm)was also investigated.
查看更多>>摘要：Dual-ion batteries(DIBs)have attracted great attention due to their affordable prices,environmental friendliness,and high operating voltage.However,the conventional graphite anode in DIBs has draw-backs such as unsatisfactory capacity and worrying safety.MoS2 is considered to be a competitive anode material that exhibits large capacity due to its unique layered structure for cation insertion/extraction.Nevertheless,the sluggish reaction kinetics of MoS2 does not match the cathode side,which makes the constructed full DIBs show poor rate ability.Here,a flower-like MoS2/polyaniline composite electrode(MoS2-PANI)where PANI was grown in situ between layers of MoS2 nanosheets was designed.In this design,the inserted PANI can broaden the layer distance of MoS2 to facilitate cation diffusion and pre-vent the restacking of nanosheets.Furthermore,PANI is also expected to increase the conductivity and relieve the volume changes during repeated charge/discharge cycles.Benefiting from that,the MoS2-PANI electrode delivered a reversible capacity of 561.91 mA h g-1 at 5 A g-1 in half-cell test.Moreover,when coupled with a mildly expanded graphite(MEG)cathode,the obtained MEG//MoS2-PANI DIB shows ex-cellent rate ability with.a reversible discharge capacity of 86.62 mA h g-1 and a desirable energy density of 308.83 W h kg-1 at 20 C.These results provide some inspiration for the design of high-rate DIBs.
查看更多>>摘要：Strength and ductility are typically mutually exclusive in traditional copper-steel joints.This work pro-poses a strategy to overcome the inherent trade-off between strength and ductility through high speed electron beam welding with a preferred deflection to facilitate the in-situ formation of Fe-rich particles in the Cu matrix.The Fe-rich particles with an average diameter of 178.5 nm feature a 3D spatial network distribution across practically the entire joint.The obtained joint reinforced with such Fe-rich particles achieves ultimate high tensile strength(413 MPa)while maintaining excellent ductility(22％).The im-proved strength of the copper-steel joint is derived from the combined effects of dislocation strengthen-ing and grain refinement strengthening,while the increase in room-temperature ductility is mainly due to the high Schmid factor up to 0.454,which promotes the primary slip system to initiate easily during tensile deformation.This work provides a novel perspective on creating copper-steel joints in terms of achieving microstructural refinement and outstanding strength-ductility synergy.
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