查看更多>>摘要：With the rapid development of electronic technology,how to effectively eliminate electromagnetic pollu-tion has become a serious problem.Perovskite oxides have shown great potential in the field of electro-magnetic wave absorption due to their unique structure and excellent physicochemical properties.Herein,by rationally manipulating the A-site ion substitution strategy,the theoretically directed doping of Sr ions into La ionic sites was utilized and the layered MoS2 was loaded by the hydrothermal process to modify its surface.Consequently,the introduced polarization phenomenon improved the dielectric performance of the perovskite oxides,achieving a collaborative dielectric/magnetic loss mechanism.Accordingly,the prepared La0.7Sr0.3FeO3(LSFO)/MoS2 as coating filler in the epoxy resin coating system can obtain the minimum reflection loss of-67.09 dB at 1.9 mm and the maximum effective absorption bandwidth of 7.28 GHz at 2.3 mm.More importantly,it also exhibits excellent absorption performance for multi-band electromagnetic waves,covering a wide range of specified frequency bands.It provides inspiration for ex-ploring novel perovskite oxide-based electromagnetic wave absorbing coatings and broadens the choice of ideal candidate materials for designing highly efficient,multi-band absorbers to cope with sophisticated electromagnetic environments.
查看更多>>摘要：Design of multi-functional microwave absorption materials with strong dissipation ability is a practical approach to address the current issue of electromagnetic radiation pollution.Herein,based on the ex-change bias interaction between ferromagnetic and anti-ferromagnetic interfaces,a series of absorbers composed of the porous biochar loaded with ferromagnetic/anti-ferromagnetic NiCO2O4/CoO were suc-cessfully prepared via a fairly simple process of one-step calcination.By regulating the calcination tem-perature,the pore size and porosity of porous carbon,morphology of loaded NPs as well as the elec-tromagnetic response property and impedance matching characteristic in such composites can be mod-ulated.The porous biochar/NiCO2O4/CoO composite prepared under 350 ℃ possesses a remarkable elec-tromagnetic absorption reflection loss(RL)of-48.41 dB at 9.12 GHz with 2.5 mm thickness,and the effective absorption bandwidth(EAB)of 4.32 GHz with 2.2 mm thickness is located at X band,this is owing to the strong coupling effect of multiple dielectric polarizations,magnetic resonances,and eddy current consumption under matched impedance.In addition,the microwave absorbing patch prepared with this composite exhibits a well-hydrophobic property for self-cleaning function,and the large exten-sibility with substantial breaking strength endows its practical usage as a flexible absorber.
查看更多>>摘要：Reducing the hot working temperature and high-temperature deformation resistance of titanium alloy to improve hot rolling and hot extrusion workability of products with thin walls and complex section shapes has always been an important topic in the field of titanium alloy processing.This paper proposed a strategy of adding Mo and Fe elements to simultaneously reduce the hot working temperature and high-temperature deformation resistance of Ti-6Al-4V alloy.The effects of Mo and Fe contents on the mi-crostructure,β transus temperature(Tp),and high-temperature flow stress(HFS)of Ti-6Al-4V-xMo-xFe(x=0-5)alloys were investigated.The results showed that adding Mo and Fe can substantially reduce the Tp and HFS of the alloy,and greatly improve its room-temperature strength.Compared with com-mercial Ti-6Al-4V samples,the Tβ of Ti-6Al-4V-2Mo-2Fe and Ti-6Al-4V-3Mo-3Fe samples was decreased by 68-98 ℃,and the HFS at 800-900 ℃ was decreased by 37.8％-46.0％.Compared with hot-rolled Ti-6Al-4V samples,the room-temperature tensile strength of hot-rolled Ti-6Al-4V-2Mo-2Fe samples was increased by about 30％,while the elongation hardly decreased.The increased strength was mainly at-tributed to fine grain strengthening and solid solution strengthening.The hot workability and room-temperature strength of Ti-6Al-4V alloy can be significantly improved by adding 2-3 wt.％Mo and Fe simultaneously.
查看更多>>摘要：Mg-Li alloy is a lightweight hydrogen storage material with high hydrogen capacity,but its poor kinetics limited its practical applications.In this work,MCM-22 molecular sieve was added to Mg-Li alloy by friction stir processing(FSP)as the catalyst to enhance the kinetic properties of Mg-Li alloy(denoted as Mg-Li-MCM-22).The resulting Mg-Li-MCM-22 possesses the reversible hydrogen storage capacity of ca.6 wt.％and can release 5.62 wt.％hydrogen within 50 min at 623 K,showing improved kinetics.The Chou model and Johnson-Mehl-Avrami-Kolmogorov(JMAK)model calculations reveal that the lattice defects generated by FSP improve the kinetics of hydrogen adsorption/desorption.The pinning effect of MCM-22 particles produces more grain boundaries and dislocations,thus,increasing the diffusion rate of hydrogen atoms and providing more nucleation sites,therefore,reducing the dehydrogenation activation energy.This work provides a new strategy for the preparation of hydrogen storage materials.
查看更多>>摘要：Hot isostatic pressing(HIP)is usually applied to reduce the defects including cracks and pores in the materials prepared by laser powder bed fusion(LPBF).In the present research,in order to improve the relative density and mechanical property,HIP was employed on the LPBF-processed Al-Cr-Fe-Ni-V high-entropy alloy(HEA)with microcracks and pores.The microstructure evolution and property improvement induced by HIP were investigated.In the LPBF-processed HEA,the microcracks were caused by residual stress and element segregation,and these microcracks as well as the pores reduced significantly after HIP treatments.Remarkably,HIP temperature has a more critical effect on the microcrack closure than the holding time,thus,microcracks and pores still existed after HIP-1 treatment(1273 K,8 h),while HIP-2 treatment(1473 K,4 h)could close the microcracks significantly.The crack closure was attributed to the interfacial diffusion of the alloying element under high temperature accompanied by high pressure,and the degree of element diffusion at both interfaces of the cracks determined the bonding strength after crack closure.Higher temperatures at high pressure induced more adequate element diffusion and higher bonding strength.The above high temperature and high pressure also induced the growth of the L12 phase and the precipitation of the B2 phase in HEA.Consequently,the tensile strength and elonga-tion of the LPBF-processed HEA after HIP-2 treatment were simultaneously enhanced(80.7％and 222.5％higher than that of LPBF-processed HEA,respectively).This could be attributed to the combined effect of microcrack/pore closure and precipitation strengthening.The strengthening effect of the B2 phase and L1 2 phase accounted for 53％(dislocation by-pass mechanism)and 47％(dislocation shearing mechanism)of the total precipitation strengthening,respectively.
查看更多>>摘要：Thermal barrier coatings(TBC)on superalloy blade/vane enable an increase in turbine inlet temperature(TIT)and aero-engine efficiency.However,the deposition of dust on TBC significantly ablates superalloys and becomes a bottleneck for advanced engine development.This paper presents a comprehensive mod-eling approach,based on an experiment involving dust deposition on a TBC-coated substrate,aimed at understanding the fundamental cause of substrate ablation.The results show that a significant increase in surface roughness is obtained experimentally with dust accumulation.The temperature field within the TBC-substrate system is disturbed by surface roughening.Consequently,the film cooling is seriously destroyed.While the dust accumulated on the TBC surface also contributes to heat insulation by increas-ing the effective TBC thickness,localized overheating of the substrate occurs and then leads to ablation and premature failure of the substrate.This elucidation of the overheating mechanism could inform the development of strategies to resist dust accumulation in advanced aero engines.
查看更多>>摘要：Titanium alloys are of keen interest as lightweight structural materials for aerospace and automotive in-dustries.However,a longstanding problem for these materials is their poor tribological performances.Herein,we designed and fabricated a multiphase Ti-Mo-Ag composite(TMA)with heterogeneous triple-phase precipitation(TPP)structure by spark plasma sintering.A lamellar α-phase(αL)precipitates from the β-phase under furnace cooling conditions and maintains a Burgers orientation relationship(BOR)with β-matrix.An active eutectic transition also occurs in the titanium matrix,resulting in TiAg phase.The intersecting acicular TiAg and lamellar αL cut β grains into fine blocks and the primary equiaxed αphase also provides many interfaces with β phase,which together effectively impede dislocation move-ment and increase strength.Compared with other titanium composites,TMA with TPP microstructure gets an excellent combination of strength(yield strength 1205 MPa)and toughness(fracture strain 27％).Furthermore,the TPP structure endows TMA with strong cracking resistance,which aids in reducing abra-sive debris at high temperatures during sliding and obtaining a low wear rate.Simultaneously,Ag parti-cles distributed at grain boundaries will easily diffuse to the wear surface,in situ forming the necessary lubricating phase Ag2MoO4 with Mo-rich matrix debris via oxidation.TMA possesses excellent tribologi-cal properties with especially low wear rate of 8.0 x 10-6 mm3N-1m1 and friction coefficient(CoF)of merely 0.20 at 600 ℃.Unlike other self-lubricating composites with high volume fraction of soft ceramic lubricants,which inevitably sacrifice their mechanical strength and ductility,the composite TMA pos-sesses well-balanced strength,toughness and self-lubricating properties.It holds important implications to design other metal matrix self-lubricating composites(MMSCs)used for load-bearing moving parts.
查看更多>>摘要：Bone defects caused by tumor resection typically require bone repair materials to fill the defect sites.The development of multifunctional bone filling materials with integrated chemotherapy,photohermal therapy,and guided bone regeneration is very necessary and urgently needed.Herein,for the first time,the construction of novel multilayered Ti3C2Tx MXene(m-MXene)/nano-hydroxyaptite(nHAp)composites(m-MXene/nHAp)for bone repair is reported.The in situ growth of nHAp on multilayered Ti3C2Tx MXene is achieved through a facile hydrothermal method without using any organic additives.Due to the syner-gistic effects of nHAp and m-MXene,the m-MXene/nHAp composites show superior drug carrier perfor-mance with ultra-high drug loading capacity and ultra-long drug sustained release time.The molecular dynamics simulation results indicate that both Ti3C2Tx MXene and HAp show many adsorption sites and high binding energy with DOX.Moreover,the m-MXene/nHAp composites possess high photothermal conversion efficiency and excellent photothermal stability.The in situ growth of nano-HAp can signifi-cantly improve the biocompatibility of the m-MXene.The as-prepared multifunctional m-MXene/nHAp composites in this work can be used as bone filling powder and have great potential in bone defect reconstruction caused by bone tumor.
查看更多>>摘要：High strength and low corrosion resistance are always the contradiction in Al-Si-Cu-Mg cast alloy due to introducing high Cu and Mg levels.In this work,the new strategy was achieved for enhancing corrosion resistance and mechanical properties by regulating multi-scale microstructure characteristics in Al-9Si-4.2Cu-0.25Mg-Zr alloy.Electrochemical and corrosion morphology results indicate that the addition of Zr significantly enhances the corrosion resistance of the alloy.The grain refinement inhibits the charge transfer process between cathode phases and the matrix is the main reason at the Zr level of less than 0.15％.When the Zr level is up to 0.3％,the multi-scale synergistic effect of grain refinement and passive film enhancement significantly inhibits the corrosion process.Moreover,0.3％Zr addition increases the yield strength to 419 MPa,tensile strength to 490 MPa,and the acceptable fracture elongation to 3.8％.The strengthening of mechanical and corrosion properties originates from the nano-Al3Zr precipitates after T6 treatment.This study provides a novel micro-mechanism and design strategy for simultaneously improving corrosion resistance and enhancing the mechanical properties of Al-Si-Cu-Mg cast alloy.
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