查看更多>>摘要：The microstructure evolution and micromechanical behaviors of additively manufactured 18Ni300 marag-ing steel for both as-printed and aged one were investigated using the in situ high-energy X-ray diffrac-tion(HE-XRD)technique with uniaxial tensile tests.The investigations revealed that the volume frac-tion of reversed austenite increased as the annealing temperature rose.The maraging steel was strength-ened by η-Ni3Ti precipitates,where the aged maraging steel had a higher UTS value of～1860 MPa than～1135 MPa in the as-printed one,but sacrificed more than half of ductility(from～8.6％to～4.0％).The austenite in aged steel presents more stability induced by the aging process than that in as-printed counterpart,which has a higher critical martensitic transformation stress of～1200 MPa than that of～780 MPa in as-printed steel.The austenite grains orientated with[200]//LD yield before the macro-yielding and preferential martensite transformation occurs.This study provides further insight into the intricated micromechanical responses of additively manufactured 18Ni300 maraging steel,enlarging the scope of its adaptation and application.
查看更多>>摘要：The hot deformation behaviors of nickel-based oxide dispersion strengthened(ODS)superalloys fabri-cated by mechanical alloying(MA)and hot extrusion(HEX)were investigated,the hot compression tests were performed to obtain true stress-true strain curves,the influence of strain rate and temperature connected with the microstructure evolution was analyzed,and the processing map and microstructure proposed at different strain levels was used to select its hot working parameters.The results illustrated that hot working conditions,especially the temperature,strongly influenced the grain structure.Specifi-cally,deforming under high temperatures and low strain rate conditions enhances dynamic softening via dynamic recovery(DRV),dynamic recrystallization(DRX),and grain growth to consume the stored strain energy.In addition,the size and morphology of nanoparticles are not significantly changed before and after deformation,the nanoparticles and the matrix still maintain a good interface combination,and no interfacial mismatch such as nanosvoids between the nanoparticle and matrix is detected due to their outstanding interfacial binding ability and excellent ductility of matrix.
查看更多>>摘要：The inverse relationship between the saturation magnetic flux density(Bs)and coercivity(Hc)of Fe-based amorphous alloys is a very active research topic that has been extensively debated.In this work,we conducted a detailed investigation on the magnetic softness of Fe83.2-xCoxB10C6Cu0.8(x=0 and 6 at.％)amorphous alloys based on analysis of the surface morphology,microstructure,magnetic anisotropy,and magnetic domain structure.Enhanced magnetic softness-magnetization synergy was realized in the present alloys by magnetic field annealing(MFA)during the de-stressing process.A dramatic 84％re-duction of Hc to 2.2 A/m was achieved for the Co-doped alloy under MFA,exhibiting excellent magnetic performance with a superb Bs of 1.86 T.The consistency between the experimental results and theoreti-cal analysis revealed that the MFA process can mitigate the trade-off between stress-induced anisotropy and induced uniaxial anisotropy owing to the homogenized structure formed by field annealing.Thus,the process favored a low Hc due to the significant continuous decline in the total magnetic anisotropy,which coincided well with the results of Magneto-optical Kerr microscopy.The study elucidates a mech-anism for tuning Hc in Co-doped alloy systems and affords a possible pathway for softening amorphous alloys with high Bs.
查看更多>>摘要：Strength-ductility trade-off is usually an inevitable scenario in κ'-carbides strengthened austenitic lightweight steel.The reduction of ductility is primarily attributed to the shearing of coherent κ'-carbides by dislocations,resulting in strain localization and ultimately leading to a low work hardening rate.Semi-coherent B2 particles,on the other hand,effectively enhance the work hardening capability due to the non-shearable feature.However,achieving a large volume fraction and uniform distribution of B2 par-ticles within the austenite matrix,as well as optimizing their morphology as fine particles,remains a challenge for austenitic lightweight steel.In this study,we have addressed the above challenges by im-plementing the two-step aging process combined with pre-cold rolling process.The pre-cold rolling treat-ment,performed prior to the initial aging treatment at 900 ℃,effectively promotes the heterogeneous nucleation of B2 particles by introducing dislocations,resulting in a more uniform distribution of B2 par-ticles and a refinement in size(with an average length of 200-500 nm and a width of 50-80 nm).Fur-thermore,these intragranular B2 particles exhibit the typical K-S and N-W orientation relationships with the austenite matrix.Subsequently,after the second-step aging process at 450 ℃,spherical nano-sizedκ'-carbides(5 nm)are homogeneously dispersed within the austenite matrix.The above dual nanoparti-cles provide an approximate precipitation hardening effect of 400 MPa.Concurrently,the nanoscale"pla-nar slip and dislocation bow-out"multiple deformation mechanisms contribute to an efficient source of work hardening capability,leading to a beneficial synergy of strength-ductility.This promising strategy is expected to expand the applications of dual-nanoprecipitation austenitic low-density steel in various lightweight structural materials.
查看更多>>摘要：Stretchable strain sensors have great potential for diverse applications including human motion detection,soft robotics,and health monitoring.However,their practical implementation requires improved repeata-bility and stability along with high sensing performances.Here,we utilized spiky vertical graphene(VG)sheets decorated on carbon nanofibers(VG@CNFs)to establish reliable conductive networks for resistive strain sensing.Three-dimensional(3D)VG@CNFs combined with reduced graphene oxide(rGO)sheets were simply coated on stretchable spandex fibers by ultrasonication.Because of the spiky geometry of the VG sheets,VG@CNF and rGO exhibited enhanced interactions,which was confirmed by mode I frac-ture tests.Due to the robust conductive networks formed by the VG@CNF and rGO hybrid,the fiber strain sensor exhibited a significantly improved strain range of up to 522％(with a high gauge factor of 1358)and stable resistance changes with minimal variation even after 5000 stretching-releasing cycles under a strain of 50％.In addition,the textile strain sensor based on the VG@CNF/rGO hybrid showed even improved repeatability for various strain levels of 10％to 200％,enabling its implementation on leg-gings for monitoring of squat posture.This study demonstrates the high potential of the 3D VG@CNF for high-performance and reliable stretchable strain sensors.
查看更多>>摘要：High-density coherent nanoprecipitates have been widely introduced into the design of new structural materials to achieve a superior strength-ductility balance.However,the thermal instability of nanostruc-tures limits their fabrication and application.In this study,we investigated the temporal evolution of nanoprecipitates in coherent nanoprecipitation-strengthened Al0.5Cr0.9FeNi2.5V0.2 high-entropy alloy dur-ing isothermal aging.When annealed at 600 ℃ for more than 100 h,we found that its nanoprecipitates were invariably stable,with no obvious changes occurring in terms of morphology and distribution.The excellent stability was mainly attributed to the restricted state of interface migration and diffusion ow-ing to the hierarchical nanostructure.The Cr-enriched nano-lamellar BCC phase divided the Cr-depleted FCC(L12)matrix,forming barriers to long-range diffusion and resulting in a kinetically slow coarsening rate.As the nano-lamellar BCC phase spheroidized as the aging temperature increased to 700 ℃,the diffusion barriers were destroyed.Remarkable coarsening occurred after that,which further verified the significant effect of the nano-lamellar BCC phase on the microstructural stability.These results provide a paradigm for designing alloys stabilized via hierarchical nanostructure,achieving good strength-ductility synergy while excellent thermal stability.
查看更多>>摘要：In this work,we investigated the mechanical properties and corresponding deformation mechanisms of an Al1Mg0.4Si alloy,which exhibited significantly higher strength and outstanding strain hardening ca-pacity at 77 K compared to its counterparts at 298 K.The deformation mechanisms responsible for the excellent strength-ductility synergy and extraordinary strain hardening capacity at cryogenic temperature were elucidated through a combined experimental and simulation study.The results reveal the presence of numerous slip traces and microbands throughout grain surfaces during deformation at 298 K,whereas at 77 K,vague grain surfaces dominate,indicating the simultaneous operation of multiple slip systems.Transmission electron microscopy(TEM)analysis using the two-beam diffraction technique demonstrates the presence of dislocations with several different Burgers vectors inside a grain at cryogenic tempera-ture,confirming the activation of multiple slip systems.The accumulation of dislocations facilitated by these multiple slip systems,combined with the high dislocation density,contributes to strain harden-ing and remarkable uniform elongation at 77 K.A modified dislocation density-based crystal plasticity model,incorporating the effect of grain boundary hardening(GBH)and temperature,was developed to gain a better understanding of the underlying mechanisms governing alloy's strength and plasticity.The GBH effect significantly enhances statistically stored dislocation(SSD)density and screw dislocation pro-portion,which promote homogeneous deformation and enhance strain hardening capacity at cryogenic temperature.These findings deepen the understanding of plastic deformation at cryogenic temperatures and pave the way for the development of ultrahigh-performance metallic materials for cryogenic appli-cations.
查看更多>>摘要：Supercapacitors(SCs)play a crucial role in flexible electronics,necessitating innovative approaches to enhance surface faradaic reactions and minimize faradaic diffusion while using aqueous electrolytes.Thus,the urea treatment of cobalt oxide(CoOx)-decorated carbon nanofibers(CNFs)is proposed in this study to decrease the contribution of faradaic diffusion-limited current.Flexible CoOx/CNF electrodes were obtained by annealing ZIF-67-grafted polyacrylonitrile(PAN)fibers via a wet chemical method.The urea treatment of CoOx/CNFs increased the content of sp2-hybridized carbon and pyridinic nitrogen,as confirmed by X-ray photoelectron spectroscopy,effectively enhancing conductivity and pseudocapacitive charge storage capability via nitrogen doping.Notably,urea-treated CoOx/CNF electrode samples exhibited a capacitance of 750 mF cm-2 at a scan rate of 10 mV s-1,while retaining more than 81％capacitance at a higher scan rate of 100 mV s-1.The cyclic voltammetry curves during variable bending angle testing(0°,45°,and 90°)exhibited negligible changes,indicating the excellent flexibility of the SCs.The CoOx/CNFs and urea-treated CoOx/CNFs exhibited 80％and 91％capacitance retentions,respectively,after 10,000 galvanostatic charge and discharge cycles.Furthermore,the attained energy densities of 76 and 61 pWh cm-2 at the respective power densities of 2 and 20 mW cm-2 indicated the excellent electrochemical performance of the optimal urea-treated CoOx/CNF electrode.
查看更多>>摘要：Fabrics,a class of carriers,have been pioneered in electromagnetic protection,but their microwave ab-sorbing potential has not been fully explored for a considerable period.Herein,aramid nanofibers(ANFs)enhanced reduced graphene oxide fabrics(ANF/rGO fabrics)were synthesized by wet spinning-chemical reduction.The ANF/rGO fabrics can achieve the minimum reflection loss(RLmin)of-15.8 dB with a thick-ness of 2.7 mm.On this basis,ANF/rGO fabrics grown with polyaniline(ANF/rGO-PANi fabrics)through in-situ doping polymerization were obtained.Polyaniline compensates for the lack of conductivity of the dielectric fabrics,bringing higher impedance matching and attenuation capability.The correspond-ing RLmin can reach-52.3 dB under 2.9 mm and the effective absorption bandwidth(EAB)increases to 6 GHz covering the whole Ku band under 2.5 mm.The fabrics woven by high-strength graphene-based hybrid fibers proposed in this study provide a new angle to achieve high-efficiency microwave absorption.
查看更多>>摘要：As one of the promising next-generation light conversion materials,indium phosphide quantum dots(InP QDs)deserve much attention due to their great optical performances and environmentally friendly prop-erties in particular.Herein,InP-based QDs are embedded into mesoporous SBA-15 and solid QDs/SBA-15 composites are prepared,which exhibit 1.5 times higher photoluminescence quantum yield(PLQY)and narrower full width of half maximum(FWHM)than traditional QDs powder thanks to the reduction of light reabsorption and the optical waveguide effect of mesoporous structure.These advantages contribute to the performance enhancement of light-emitting diodes(LEDs).The luminous efficacy of the LED with green QDs/SBA-15 is 99.49 lm/W,which is higher than that of QDs powder(66.14 lm/W).In addition,the white LED fabricated with green and red InP-based QDs/SBA-15 shows luminous efficacy of 61.38 lm/W.More importantly,the luminous efficacy of the white LED is improved to 129.62 lm/W when using the K2SiF6:Mn4+instead of red InP-based QDs/SBA-15,because the K2SiF6:Mn4+does not absorb the emis-sion from green InP-based QDs/SBA-15.This value is higher than those white LEDs with InP-based QDs reported previously.It is believed that this study demonstrates the promising potential of InP-based QDs for optoelectronic applications.
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