查看更多>>摘要：Microwave absorption(MA)materials have been captured extensive attentions due to the serious elec-tromagnetic(EM)pollution.Numerous interests focus on the MA performances of core-shell structural composites with magnetic constituents as cores and dielectric constituents as shells,which inevitably suppressed the magnetic coupling causing the decrease of magnetic loss to some extent.Herein,the core-shell structural carbon(C)microsphere/magnetic metal composites were fabricated through the combi-nation of an electrostatic assembly approach and subsequent in-situ reduction reaction.The complex per-mittivity and permeability of core-shell C@magnetic metal composite system can be effective adjusted by the constituent and microstructure of shells.Thanks to the distinct magnetic coupling from the subtle designed structures and the promotion of the magnetic-dielectric synergy,the C@magnetic metal com-posite exhibited enhanced MA properties.The optimal reflection loss(RL)of C@Ni composite was-54.1 dB with a thickness of 3.4 mm,meanwhile the effective absorbing band could reach over 5.5 GHz at only a 1.8 mm thickness.Broad absorption bandwidth with RL below-10 dB could achieve 6.0 GHz and 6.7 GHz for C@Co and C@NiCo composites with a thin 2.1 mm thickness,respectively.Our exciting findings might lead a guide on the novel structure design for the functional core-shell structural composites used for microwave absorption.
查看更多>>摘要：Microbiologically influenced corrosion(MIC)is an unavoidable problem in several industries.Copper(Cu)and its alloys are widely used engineering materials.However,MIC of Cu remains a persistent chal-lenge to their performance and functional lifetime under aggressive environments.This study investi-gated nanosecond pulsed laser processing(LP),which may enhance the corrosion resistance of Cu.The microstructural evolution and corrosion behavior of LP-Cu in the presence of sulfate-reducing bacteria(SRB)were evaluated.Typical deformation-induced microstructural features of high-density dislocations were analyzed on the top surface of LP-Cu coupon.Electrochemical measurements suggested that LP-Cu coupons exhibited better corrosion resistance in SRB-inoculated solution compared with their original counterpart.The enhanced corrosion resistance by LP primarily resulted from the combined influences of compressive residual stress and work hardening in the surface.However,overlap percentage played a key role in improving corrosion resistance.LP produced optimal corrosion resistance at 50％overlap.There-fore,this study introduces a unique and an option for anticorrosion control in manufacturing processes and potentially implements it onto other materials to improve its microbial corrosion resistance through LP.
查看更多>>摘要：60NiTi alloy is considered to be a promising material for specialized bearing and gear applications due to its high hardness,strength,and low modulus.However,fabricating 60NiTi through conventional pro-cessing methods is challenging due to the brittleness and poor workability.In this study,60NiTi with high relative density was successfully fabricated directly from pre-alloyed powder through hot isostatic pressing.The effects of solution and aging treatments on microstructure and mechanical properties were systematically studied by advanced characterization techniques.The hot-isostatic-pressed 60NiTi showed low average hardness and elastic strain due to the formation of a soft Ni3Ti phase and B2 NiTi matrix.Solution treatment above 1000℃dissolved the Ni3Ti phase and promoted the formation of nanoscale Ni4Ti3 precipitates,which significantly improved the hardness,strength,and elastic strain of 60NiTi.The formation of the Ni4Ti3 phase can be mainly attributed to the driving forces induced by the chemical su-persaturation and mechanical stress concentration.Finally,the phase transformation mechanisms during heat treatment and compression test were discussed.
查看更多>>摘要：The metastable α'phase and dislocation characteristics(e.g.,density and constituents)are of vital im-portance for the mechanical responses of(α+β)titanium alloys.In this work,to reveal the in-depth de-composition mechanisms of dislocations and metastable α'and their influences on mechanical properties in a Ti-6Al-4V(α+β)alloy,the thermal stability of different microstructures tailored by various cooling approaches were investigated utilizing scanning electron microscope,electron backscattered diffraction,transmission electron microscope and X-ray diffraction line profile analysis.The results showed that the initial characteristics of α'and α laths and dislocation density were influenced by the cooling methods remarkably.The thermal stability of Ti-6Al-4V alloy increased with decreasing cooling rate.The improve-ment in thermal stability can be ascribed by the decrement in dislocations,partitioning of the alloying elements and grain orientations variation of the α'lath and α phase.It is also found that the plastic strain accommodation of β→α'transformation was dominated by<a>dislocations.During stabilization annealing treatments,the<a>,<c>and<c+a>dislocations simultaneously decomposed.The decompo-sition of dislocations and metastable α'phase during various stabilization annealing and the particular twins and stacking faults microstructures formed during quenching have a great influence on the proper-ties of the studied Ti-6Al-4V alloy.
查看更多>>摘要：High performance microwave absorption(MA)materials especially those with tunable frequency are highly desirable for telecommunication industries and military camouflage in the information era.Herein,we constructed hierarchical heterostructures based on VB-group laminated vanadium disulfide(VS2)nanosheets embedded with cobalt tetroxide(Co3O4)nanoparticles.The highly dispersed Co3O4 nanopar-ticles generate strong electromagnetic coupling networks that could enhance the loss properties of MA materials.Moreover,the interconnected VS2 layered network results in dipolar/interfacial polarization,multiple reflection and scattering favorable for the enhanced MA performance.Impressively,the maxi-mum reflection loss of the VS2/Co3O4 hybrids containing 10％Co3O4 can reach 57.96 dB at a thin thick-ness of 1.57 mm,and the bandwidth with an RL value less than-10 dB is as large as 3.5 GHz.The effective MA band could be adjusted in a range of 15.1 GHz(2.9-18 GHz)from S to Ku bands by the in-crease in thickness from 1.2 mm to 5.5 mm.The results show that the synergistic effect of multiple loss mechanisms and good impedance matching could be the reasons for strong MA capability in nearly all frequency bands,and thus,the high-performance and lightweight MA materials could be developed by the VS2/Co3O4 hybrids.
查看更多>>摘要：The(CrNbTiAlV)Nx high-entropy nitride films were fabricated by adjusting nitrogen flow via magnetron sputtering.The microstructure,mechanical,electrochemical and tribocorrosion performances of the films were studied.The results show that the films transform from amorphous to nanocrystalline structure as nitrogen flow increased.The nanocrystalline films show super hardness(＞40 GPa)and adhesion strength(＞50 N).The amorphous film has a pretty anti-corrosion in static corrosion,while not in tribocorrosion condition.The film deposited at nitrogen flow of 38 sccm exhibits the optimal tribocorrosion performance in artificial seawater,with the highest open circuit potential(～-0.1 V vs.Ag/AgCl),the lowest friction coefficient(～0.162)and wear rate(～7.48×10-7 mm3 N-1 m-1).
查看更多>>摘要：Al-Mn-Fe-Si strips were fabricated via both the twin-roll casting(TRC)and the more conventional route,direct-chill casting(DC).The two types of strips prepared were subjected to thermal exposure at a series of temperatures.Uniaxial tensile tests after the thermal exposure showed that while the DC strip pre-sented a～74％decrease in the yield strength and～35％decrease in the ultimate tensile strength(UTS)after being exposed to 350℃for 12 h,the TRC strip,in contrast,maintained its strength at tempera-tures up to～460℃for the same duration.Systematic microstructure characterization revealed that the different thermal stability in the strength of the two types of strips arised from their distinct evolution in grain morphology and second phase particles during the thermal exposure.The calculation based on Cahn-Lucke-Stuwe(CLS)model suggested that due to the highly supersaturated solute atoms,at the be-ginning of the thermal exposure,the TRC strip experienced a strong solute drag which reduced the grain boundary migrating velocity to a value that is orders of magnitude smaller than that in the DC strip.With the progress of the thermal exposure,the solute atoms precipitated out,forming densely distributed sec-ond phase particles.For one thing,these particles stabilized the grain structure by inducing Zener pinning pressure which could be ten times higher than that in the DC strip,depending on the temperature.For another,they acted as dislocation obstacles and compensated for the strength loss owing to decreasing solution hardening.Both effects contributed to the TRC strip's fairly stable strength regarding thermal exposure below 460℃.The present work could guide the direct application of the TRC strips in the in-dustry.The results should also be helpful for the development of a fundamental framework for designing advanced TRC Al strips with improved mechanical properties at elevated temperatures.
查看更多>>摘要：The effect of aging treatment on the microstructure and corrosion behavior of a Fe-18Cr-15Mn-0.66N high-nitrogen stainless steel(HNSS)in 3.5 wt.％NaCl solution was investigated using a series of elec-trochemical tests,scanning electronic microscopy(SEM),X-ray diffraction(XRD)and X-ray photoelectron spectroscopy(XPS).The results showed that the aging treatment led to the precipitation of Cr2N parti-cles along the grain boundaries and their morphologies changed from dispersive particles to continuous network as the aging time increased up to 60 min.Aging time had minor effects on the corrosion poten-tial and corrosion current density,but resulted in the sharp decrease in the pitting corrosion potential.The passive film behaved as a n-type semiconductor,and the donor density of the passive film increased with the aging time.Meanwhile,the fraction of stable oxide(Cr2O3)in the passive film decreased with the aging time.It demonstrates that the aging treatment deteriorated the protectiveness of the passive film,hence weakened the corrosion resistance of HNSS.
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