查看更多>>摘要：Advanced electromagnetic (EM) wave absorbers with wide bandwidth is crucial to avoid EM interference and radiation,while achieving compensational attenuation at different frequencies is challenging.Herein,two-dimensional (2D) sandwiched FeNi@SnO2 have been designed,for which SnO2 nanosheets provide numerous heterogeneous nucleation sites for the growth of dispersive FeNi nanoparticles with reduced size.The SnO2 exhibits dipole polarization at 21.45 GHz with a width of ～4.00 GHz,while the FeNi nanoparticles induce exchange resonance at 18.13 GHz (～6.00 GHz width) and interfacial polarization at 15.97 GHz (～6.00 GHz width).Such complementary attenuation mechanisms give rise to an impressive ultra-wide effective absorption bandwidth of 11.70 GHz with strong absorption of-49.1 dB at a small thickness of 1.75 mm.Not only superior EM wave absorption is achieved in this work,it also provides a versatile strategy to integrate different loss mechanisms in the design of EM wave absorbers with extra-wide bandwidth.
Lei HeZhiLei WangHiroyuki AkebonoAtsushi Sugeta...
9-19页
查看更多>>摘要：To predict the fatigue life for oblique hyperbola-and bilinear-mode S-N curves of metallic materials with various strengths,a machine-learning approach for direct analysis was employed.Additionally,to determine the fatigue limit of the utilized materials (AISI 316,AISI 4140 and CA6NM series) with different S-N curve modes using finite-fatigue life data,a Bayesian optimization-based inverse analysis was performed.The results indicated that predictions of the fatigue life for the utilized datasets via the random forest (RF) algorithm for AIS14140 and CA6NM,and artificial neural network (ANN) for AISI 316,distribute within 2 factor error lines for most data.In the Bayesian optimization-based inverse analysis,the specific explanatory variabl.es corresponding to the optimized maximum fatigue life were treated as the fatigue limits.The predicted fatigue limits either approximated to or slightly underestimated the experimental results,except for several cases with large errors.Using the inverse analysis to predict the fatigue limit for both S-N curve modes is applicable for current employed data-set.However,the explored maximum fatigue lives via BO corresponding to the predicted fatigue limit were underestimated for AISI 4140 and CA6NM,and was overestimated for AISI 316 because of effect of shape of S-N curves.By combining the ANN or RF direct and BO inverse algorithms,whole S-N curves (including the fatigue limit) were evaluated for the S-N curve shapes of the oblique hyperbola and bilinear modes.
查看更多>>摘要：Implementation of novel γ/γ'Co-based superalloys with higher strength and improved creep durabil-ity is a challenging task for researchers.The lack of atomic-level understanding of plastic deformation behavior has seriously limited the exploration of the full capacity of Co-based alloys.We put forward a comprehensive study of generalized stacking fault energies by first principles to explore the effect of Ni and Al/W on the plastic deformation mechanism of γ'precipitates in Co-based superalloys.It is found that alloying Ni and adjusting Al/W obviously change the dislocation glide and twinning nucleation in the γ'precipitates by altering the stable fault energies and the unstable fault energy barriers.Excessive ad-dition of either Ni or W deteriorates the strength even the stability of alloys.The ratio of effective planar fault energy (△Ep) bridges intrinsic energy barriers and various deformation mechanisms of superalloys at elevated temperatures.Except for alloying effects,the grain orientation also significantly governs the operation of the plastic deformation of superalloys.Our theoretical results agree with the available mea-surements and well capture the observed phenomena in experiments.
查看更多>>摘要：Liquid phase sintering (LPS) is a proven technique for preparing large-size tungsten heavy alloys (WHAs).However,for densification,this processing requires that the matrix of WHAs keeps melting for a long time,which simultaneously causes W grain coarsening that degenerates the performance.This work develops a novel ultrashort-time LPS method to form bulk high-performance fine-grain WHAs based on the principle of laser additive manufacturing (LAM).During LAM,the high-entropy alloy matrix(Al0.5Cr0.9FeNi2.5V0.2) and W powders were fed simultaneously but only the matrix was melted by laser and most W particles remained solid,and the melted matrix rapidly solidified with laser moving away,producing an ultrashort-time LPS processing in the melt pool,i.e.,laser ultrashort-time liquid phase sin-tering (LULPS).The extreme short dwell time in liquid (～1/10,000 of conventional LPS) can effectively suppress W grain growth,obtaining a small size of 1/3 of the size in LPS WHAs.Meanwhile,strong convection in the melt pool of LULPS enables a nearly full densification in such a short sintering time.Compared with LPS WHAs,the LULPS fine-grain WHAs present a 42％ higher yield strength,as well as an enhanced susceptibility to adiabatic shear banding (ASB) that is important for strong armor-piercing capability,indicating that LULPS can be a promising pathway for forming high-performance WHAs that surpass those prepared by conventional LPS.
查看更多>>摘要：The shuttle effect of lithium polysulfides (LiPSs) and sluggish redox conversion significantly hinder prac-tical implementation of lithium-sulfur batteries (LSBs).To overcome these issues,herein,we present MoP quantum dots anchored N,P-doped graphene (MPQ@G) as a multifunctional LSB cathode.The N,P-doped graphene layers serve as a conductive skeleton to support the MoP QDs which can accelerate the electron transfer,physically hinder the polysulfide migration and thus enhance the electrochemical performance.More importantly,as a polar and conductive catalyst,MoP QDs provide catalytically active sites for the conversion of LiPSs.As a result,the LSBs with MPQ@G/S cathodes deliver an elevated initial capacity of 1220.2 mAh g-1 at 0.2 C and remain 98.9％ after rate cycles,signifying its exceptional cycling stability.Moreover,it displays a large capacity of 681.2 mAh g-1 even at a high rate of 1 C.The Li-S pouch cell also presents high specific capacities and preeminent cycling stabilities,confirming its great potential for high-rate applications.Density functional theory calculations demonstrate the improved absorptivity and redox conversion reversibility of LiPSs.This work provides an efficient strategy to improve composite with highly adsorptive and catalytic properties for high-performance Li-S batteries.
查看更多>>摘要：Inconel 738 LC samples were fabricated using laser powder bed fusion under continuous-wave and pulsed-wave modes.Microstructure,surface quality and mechanical properties were compared to eval-uate the printing quality between these 2 laser beam modes.The results show that the application of pulsed wave could effectively eliminate cracking in the as-fabricated sample,despite 0.046％ porosity generated.Further microstructure analysis revealed that the refinement of grains by the pulsed-wave laser beam was the main contributor in eliminating the cracks.And this refinement was ascribed to the higher cooling rate under the discontinuous radiation of laser beam proofed by the numerical simulation.And the pore formation was related to Rayleigh instability and residual bubbles in the sample under the pulsed-wave mode,while pores were less detrimental to the mechanical properties than cracks.There-fore,the part under the pulsed-wave mode exhibited superior mechanical performance compared to that under the continuous-wave mode.
查看更多>>摘要：The effect of amorphous film on the deformation mechanism and mechanical properties of 6H-SiC were systematically explored by a combination of both experiments and molecular dynamic (MD) simulations in nanoindentation.The experimental results showed that the plastic deformation of surface-modified 6H-SiC is mainly accommodated by dislocation activities in the subsurface and an amorphous layer with uniform thickness.The MD results indicated that the amorphous layer on the surface of the residual indentation mark consists of both amorphous SiO2 and SiC due to direct amorphization.In addition,the amorphous SiO2 film undergoes densification and then ruptures with the indentation depth increases.The modulus and hardness increase with increasing the indentation depth at the initial stage but will reach their stable values equivalent to monocrystalline 6H-SiC.
查看更多>>摘要：Metastable phase in tungsten film is of great interests in recent years due to its giant spin Hall effects,however,little information has been known on its nucleation,growth and phase transformation.In this paper,a 900 nm-thick tungsten film with double-layer structure (α-W underlayer and β-W above it) was produced on SiO2/Si substrate by high vacuum magnetron sputtering at room temperature.The structural properties of β-W were systemically investigated by X-ray diffraction,transmission electron microscopy,thermodynamic calculation,first-principle and phase-field simulations.It is found that the β-W nucle-ation is energetically favoured on the SiO2 surface compared to the α-W one.As the film thickening pro-ceeds,β-W[211]turns to be preferred direction of growth owing to the elastic strain energy minimiza-tion,which is verified by phase-field simulations.Moreover,the β→α phase transformation takes place near the film-substrate interface while the rest of the film keeps the β-W phase,leading to a double-layer structure.This localized phase transition is induced by lower Gibbs free energy of α-W phase at larger grain sizes,which can be confirmed by thermodynamic calculation.Further in-situ heating TEM analysis of the as-deposited film reveals that the β→α phase transformation is fulfilled by α/β inter-face propagation rather than local atomic rearrangements.Our findings offer valuable insights into the intrinsic properties of metastable phase in tungsten.
查看更多>>摘要：Daylighting structures,including solar cells and building windows,utilize sunlight whilst suffering from undesired solar heat and outdoor dust contamination.A radiative cooling system that is transparent to sunlight and has a superhydrophobicsurface would cool and clean the daylighting structures in a sus-tainable manner.However,the majority of the current daytime radiative cooling systems were designed to fully reflect the incident sunlight to maximize the cooling power.In this work,we optimized both the sunlight transmission and infrared thermal irradiation by modeling the size-dependent scattering and ab-sorption of light by SiO2 spheres embedded in a polymer matrix,we found that the use of nanospheres(20 nm) enabled both high sunlight transmittance (＞ 90％) and infrared emissivity (～0.85).This theo-retical prediction was confirmed by experimental measurements of a solution-processed nanocomposite film.When coated on a solar cell,the as-prepared film not only preserved the power conversion effi-ciency of the cell (14.71％,uncoated cell has an efficiency of 14.79％) but also radiatively cooled the cell by up to 5 ℃ under direct sunlight.This reduction of the operating temperature of the solar cell further enhanced its electrical power output,evidenced by an increase in the equilibrium temperature of the LED load by about 14 ℃.The nanoscale textured surface formed by the nanospheres further led to su-perhydrophobicity and thus excellent self-cleaning performance (efficient removal of dust by wind and/or water droplets).
查看更多>>摘要：In this paper,we were devoted to quantitatively analyzing the dimensional change of 2024AI alloy dur-ing the aging process.Types of precipitates have been defined and the corresponding volume fraction has been measured with Transmission Electron Microscopy (TEM) and Three-Dimensional Atom Probe Tomography (3D-APT).Guinier-Preston-Bagaryatsky (GPB) zone (0.86 vol.％) was found after aging for 8 h.GPB zone (0.17 vol.％) and S'phase (1.02 vol.％) was found after aging for 24 h.The reduced dimensional change was attributed to the reduction of matrix lattice parameter.Relative to the initial supersaturated solid solution state,the lattice strain of-2.79 × 10-5 and-5.16 × 10-5 was produced after 8 h and 24 h aging respectively.The difference of the lattice parameters between the precipitates and matrix was also considered.A model was established to quantitatively describe the relationship between the precipitation process and dimensional change of 2024Al alloy.
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