查看更多>>摘要：Similar to other metallic materials,duplex stainless steel dramatically loses its advantage of high duc-tility as they are strengthened.Here,we produce a gradient nanograined dual-phase structure in the 2101 duplex stainless steel,thus facilitating a superior strength-ductility synergy:a yield strength of 1009.5 MPa being two times higher than that of the as-received sample,a total elongation of 23.4％and a uniform elongation of 5.9％.This novel structure is produced through a processing route of ul-trasonic severe surface rolling and annealing,which realizes a superposition of gradient nanostructure and lamellar dual-phase structure with austenite and ferrite.During the tension deformation of gradi-ent nanograined dual-phase structured duplex stainless steel,a significant accumulation of geometrically necessary dislocations occurs.These dislocations are formed to accommodate the deformation incompat-ibility caused by the layer-by-layer difference in strength and hardness of individual phase domains,as well as the inherent difference in properties between the austenite and ferrite domains.This results in a stronger hetero-deformation induced strengthening and hardening significantly contributing to superior mechanical properties.Our study provides a new avenue to develop advanced steels with high strength and ductility.
查看更多>>摘要：In order to obtain high-performance electromagnetic wave absorbers,the adjustment of structure and components is essential.Based on the above requirements,this system forms a three-dimensional frame structure consisting of MXene and transition metal oxides(TMOs)through efficient electrostatic self-assembly.This three-dimensional network structure has rich heterojunction structures,which can cause a large amount of interface polarization and conduction losses in incident electromagnetic waves.Hollow structures cause multiple reflections and scattering of electromagnetic waves,which is also an important reason for further increasing electromagnetic wave losses.When the doping ratio is 1∶1,the system has the best impedance matching,the maximum effective absorption bandwidth(EABmax)can reach 5.12 GHz at 1.7 mm,and the minimum reflection loss(RLmin)is-50.30 dB at 1.8 mm.This provides a reference for the subsequent formation of 2D-MXene materials into 3D materials.
查看更多>>摘要：In the harsh service environment of high temperature and intense neutron irradiation in water-cooled nuclear reactors,the austenitic stainless steel weld overlay cladding on the inner surface of the reac-tor pressure vessel suffers from thermal aging and irradiation damage simultaneously,which can induce microstructural evolution and hardening of the material.Since it is quite difficult to achieve this simul-taneous process out of the pile,two kinds of combined experiments,i.e.,post-irradiation thermal aging and post-aging irradiation were performed on 308 L stainless steel weld metals in this work.The in-teractive effect of thermal aging and proton irradiation on microstructural evolution and hardening ofδ-ferrite in 308 L weld metal was investigated by combining atom probe tomography,transmission elec-tron microscopy and nanoindentation tests.The results revealed that thermal aging could eliminate the dislocation loops induced by irradiation and affect the phase transition process by accelerating spinodal decomposition and G-phase precipitation,thus enhancing hardening of irradiated δ-ferrite.For the ef-fect of irradiation on the microstructure and hardening of thermally aged δ-ferrite,however,intensive collision cascades can intensify G-phase precipitation and dislocation loop formation but decrease spin-odal decomposition,leading to a limited effect on hardening of thermally aged δ-ferrite.Furthermore,the interaction of thermal aging and irradiation can promote G-phase precipitation.Meanwhile,the interac-tion can cause 8-ferrite hardening,which is mainly influenced by spinodal decomposition,followed by G-phase and dislocation loops,where spinodal decomposition and G-phase cause hardening by inducing strain fields.
查看更多>>摘要：Due to the easy coarsening caused by poor thermal stability,the verified annealing-induced hardening in nanograined metals can only maintain at a relatively low-temperature range.In this study,a nanolam-inated(CrCoNi)97.4Al0.8Ti18 medium-entropy alloy with an average lamellae thickness of～20 nm em-bedded by thinner nanotwins was fabricated by severe cold rolling to achieve superior thermal stability.Compared with the conventional nanotwinned CrCoNi with nanotwins inside ultra-fined grains,the hier-archical nanolaminated-nanotwinned(CrCoNi)97.4Al0.8Ti18 exhibits a significant annealing-induced hard-ening effect,i.e.,hardness increasing from～250 HV in the original specimen to～500 HV in the cold-rolled status and finally～630 HV after annealing at 600 ℃ for 1 h.Detailed microstructure charac-terizations reveal that the reduced dislocation density and formation of L12 ordered domain are mainly responsible for such hardening effect,which is facilitated by the effectively suppressed coarsening with annealing temperature,i.e.,slow detwinning process and well-retained low-angle nanolamellar structure.The coarsening mechanisms from the cold-rolled nanolamellae to the fully recrystallized micro-equiaxed structures under the annealing temperatures ranging from 400 to 800 ℃ were also elucidated by atomic observations.
查看更多>>摘要：In this study,a Ni-Fe metal-organic framework modified by-NH2 and-SH was synthesized using a sim-ple hydrothermal process for enhancing photocatalytic CO2 reduction.As expected,the N2S-NiFe(NH2-BDC/H4DSBDC,2∶1)displayed excellent photocatalytic CO2 reduction activity and high CO selectivity(12,412.23 μmol g-1 h-1)under visible light irradiation(λ ≥ 420 nm),which is 5 times that of NiFe-MOF.Notably,the excellent photocatalytic performance of N2S-NiFe can benefit from the rich defect trap site caused by the introduction of amino and sulfhydryl groups,accelerating charge transfer and promot-ing space charge separation,as supported by the photo-electrochemical properties.To better understand the CO2 adsorption mechanism,density functional theory calculations were performed,which revealed that the Niov site has more negative adsorption energy compared with the Feov site.This study pro-vides a simple strategy to establish efficient photocatalysts for CO2 reduction through the modification of organic ligands.
查看更多>>摘要：The glass-forming ability and mechanical properties of metallic glasses and their composites are well known to be sensitive to the preparation conditions and are highly deteriorated by industrial preparing conditions such as low-purity raw materials and low vacuum.Here,we showed that a series of in-situ bulk metallic glass composites(BMGCs)which exhibit excellent ductility and segmental work harden-ing were successfully developed utilizing a high vacuum high-pressure die casting(HV-HPDC)technology along with industrial-grade raw materials.The tensile properties of these BMGCs are systematically inves-tigated and correlated with the alloy microstructure.As compared with the copper mold suction casting method,the volume fraction difference of the dendrite phase for the BMGCs with the same composition is not significant when fabricated by the HV-HPDC,whereas the size of the β-phase is generally larger.In-situ BMGCs with the composition of Ti48Zr20(V12/17Cu5/17)19Be13 obtained by the HV-HPDC process show ductility up to 11.3％under tension at room temperature and exhibit a certain amount of work hardening.Two conditions need to be met to enable the BMGCs,which are prepared by vacuum die-casting to retain favorable ductility:(1)The volume fraction of β phase stays below 62％±2％;(2)The equiaxed crystals with a more uniform size in the range of 5-10 µm.Meanwhile,the results of the present study provided guidance for developing BMGCs with good ductile properties under industrial conditions.
查看更多>>摘要：Graphene(Gr)reinforced high-entropy alloy(HEA)matrix composites are expected as potential candi-dates for next-generation structural applications in light of outstanding mechanical properties.A deep comprehension of the underlying deformation mechanisms under extreme shock loading is of paramount importance,however,remains lacking due to experimentally technical limitations in existence.In the present study,by means of nonequilibrium molecular dynamics simulations,dynamic deformation behav-iors and corresponding mechanisms in equiatomic FeNiCrCoCu HEA/Gr composite systems were investi-gated in terms of various shock velocities.The resistance to dislocation propagation imparted by Gr was corroborated to encourage the elevated local stress level by increasing the likelihood of dislocation inter-plays,which facilitated the onset of twins and hexagonal close-packed(HCP)martensite laths.Meanwhile,the advent of Gr was demonstrated to endow the HEA with an additional twinning pathway that induced a structural conversion from HCP to parent face-centered cubic(FCC)inside HCP martensite laths,differ-ent from the classical one that necessitated undergoing the intermediate procedure of extrinsic stacking fault(ESF)evolution.More than that,by virtue of an increase in flow stress,the transformation-induced plasticity(TRIP)effect was validated to be additionally evoked as the predominant strain accommodation mechanism at higher strains on the one hand,but which only assisted plasticity in pure systems,and on the other hand,can also act as an auxiliary regulation mode together with the twinning-induced plastic-ity(TWIP)effect under intermediate strains,but with enhanced contributions relative to pure systems.One may expect that TRIP and TWIP effects promoted by introducing Gr would considerably inspire a synergistic effect between strength and ductility,contributing to the exceptional shock-resistant perfor-mance of FeNiCrCoCu HEAs under extreme regimes.
查看更多>>摘要：Constructing of heterojunction was identified as a feasible way to improve photocatalytic activity of pho-tocatalyst.In this work,a n-p type Bi2WO6/AgInS2 S-scheme heterojunction was successfully prepared for organic pollutants degradation.This Bi2WO6/AgInS2 S-scheme heterojunction exhibited much higher pho-tocatalytic activity towards Rhodamine B(92.24％,expose to visible light for 60 min),norfloxacin(81.73％,expose to visible light for 90 min)and levofloxacin(87.46％,expose to visible light for 90 min)than pure Bi2WO6 and pure AgInS2.Toxicity analysis indicated the low environmental toxicity of Rhodamine B degradation intermediates for Rye seeds and Sudangrass seeds germination and growth.Mechanism study displayed that AgInS2 and Bi2WO6 work as the primary photocatalyst to form·O2-and ·OH,respectively.The improved photocatalytic activity of the Bi2WO6/AgInS2 S-scheme heterojunction was due to the im-proved light response range and intensified carrier separation capability.Additionally,a S-scheme charge transfer mechanism including multiple charge transfer channels was proposed.This work could provide an effective strategy for organic pollutants degradation in wastewater.
查看更多>>摘要：In the present work,a multi-element nanoglass(m-NG)of FeCoCrMoCBY is obtained first time by the laser ablation combined with inert gas condensation(laser-IGC)technique.Compared with the con-ventional rapid-quenched metallic glass(MG)with identical composition,the Fe-based m-NG demon-strates a superior performance as a self-supported electrocatalyst for hydrogen evolution reaction(HER)in acidic solution.The enhanced HER activity of m-NG is proposed to be closely related to its high en-ergy states,which is originated from the unique inhomogeneous nanostructures with a high density of low-coordinated atoms.Additionally,the Fe-based m-NG exhibits an outstanding comprehensive catalytic performance even beyond the commercial Pt/C catalyst in long-term test due to its self-optimization abil-ity.This work not only opens the way to the preparation of m-NGs by the novel laser-IGC technique,but also makes a great contribution to developing low-cost,high-efficient,and super-durable HER electrocat-alysts in acidic environment.
查看更多>>摘要：Recently,researchers have explored the use of precipitation strengthening and finer microstructures with high-density dislocations in additive manufacturing to produce high-entropy alloys(HEAs)with ad-justable properties.However,the inherent surface roughness and lack of machinability research in AMed HEAs limit their engineering applications.In this study,we systematically investigated the microstruc-tural characteristics,mechanical properties,and machinability of Fe29.3Co28.7Ni28.6Al6.8Ti6.6(at.％)HEAs with three different structures:single FCC phase cellular(SPC),dual precipitation-strengthened(DPS),and single precipitation-strengthened(SPS).These structures were fabricated by selective laser melting and isothermally annealing at 780 and 940 ℃.Compared to SPC HEA,DPS HEA exhibits a significant in-crease in yield strength and ultimate tensile strength but with a dramatic sacrifice in ductility.SPS HEA exhibits similar mechanical properties to SPC HEA due to the pronounced coarsening of L21 precipitates.The ultraprecision machining micro-cutting test showed that SPC HEA had a significant mechanochem-ical effect,as evidenced by a sharp drop in cutting force for inked workpieces,but not DPS HEA.An abnormal finding was that the negligible reflection of cutting force for SPS HEAs suggested a negative mechanochemical effect,even though SPS HEA had equally excellent plasticity like SPC HEA.It was found that nanocrystallization-induced strength enhancement and ductility reduction of SPS HEA lead to chips'deformation dominated by shear avalanche rather than chip folding of SPC HEA,which involves the re-duction of surface energy and friction of chips'interfaces.Overall,these results and our research findings may guide the machining of AMed precipitation-strengthened HEAs and accelerate their engineering ap-plication.
NETL
NSTL
万方数据