查看更多>>摘要：This work reveals the significant effects of cobalt(Co)on the microstructure and impact toughness of as-quenched high-strength steels by experimental characterizations and thermo-kinetic analyses.The results show that the Co-bearing steel exhibits finer blocks and a lower ductile-brittle transition temperature than the steel without Co.Moreover,the Co-bearing steel reveals higher trans-formation rates at the intermediate stage with bainite volume fraction ranging from around 0.1 to 0.6.The improved impact toughness of the Co-bearing steel results from the higher dense block boundaries dominated by the V1/V2 variant pair.Furthermore,the addition of Co induces a larger transformation driving force and a lower bainite start temperature(Bs),thereby contributing to the refinement of blocks and the increase of the V1/V2 variant pair.These findings would be instructive for the composition,microstructure design,and property optimization of high-strength steels.
查看更多>>摘要：Carbon can change the phase components of low-density steels and influence the mechanical properties.In this study,a new method to control the carbon content and avoid the formation of δ-ferrite by decarburization treatment was proposed.The microstructural changes and mechanical characteristics with carbon content induced by decarburization were systematically examined.Crussard-Jaoul(C-J)analysis was employed to examine the work hardening characteristics during the tensile test.During decarburization by heat treat-ments,the carbon content within the austenite phase decreased,while Mn and Al were almost unchanged;this made the steel with full austenite transform into the austenite and ferrite dual phase.Meanwhile,(Ti,V)C carbides existed in both matrix phase and the mole frac-tion almost the same.In addition,the formation of other carbides restrained.Carbon loss induced a decrease in strength due to the weak-ening of the carbon solid solution.For the steel with the single austinite,the deformation mode of austenite was the dislocation planar glide,resulting in the formation of microbands.For the dual-phase steel,the deformation occurred by the dislocation planar glide of aus-tenite first,with the increase in strain,the cross slip of ferrite took place,forming dislocation cells in ferrite.At the late stage of deforma-tion,the work hardening of austinite increased rapidly,while that of ferrite increased slightly.
查看更多>>摘要：Multistage heat treatment involving quenching(Q),lamellarizing(L),and tempering(T)is applied to marine 10Ni5CrMoV steel.The microstructure and mechanical properties were studied by multiscale characterizations,and the kinetics of reverse austenite transformation,strain hardening behavior,and toughening mechanism were further investigated.The lamellarized specimens possess low yield strength but high toughness,especially cryogenic toughness.Lamellarization leads to the development of film-like reversed austen-ite at the martensite block and lath boundaries,refining the martensite structure and lowering the equivalent grain size.Kinetic analysis of austenite reversion based on the JMAK model shows that the isothermal transformation is dominated by the growth of reversed austenite,and the maximum transformation of reversed austenite is reached at the peak temperature(750℃).The strain hardening behavior based on the modified Crussard-Jaoul analysis indicates that the reversed austenite obtained from lamellarization reduces the proportion of martensite,significantly hindering crack propagation via martensitic transformation during the deformation.As a consequence,the QLT specimens exhibit high machinability and low yield strength.Compared with the QT specimen,the ductile-brittle transition temperature of the QLT specimens decreases from-116 to-130℃ due to the low equivalent grain size and reversed austenite,which increases the cleavage force required for crack propagation and absorbs the energy of external load,respectively.This work provides an idea to im-prove the cryogenic toughness of marine 10Ni5CrMoV steel and lays a theoretical foundation for its industrial application and compre-hensive performance improvement.
查看更多>>摘要：Ti-6Al-4Zr-2Sn-6Mo alloy is one of the most recent titanium alloys processed using powder bed fusion-laser beam(PBF-LB)technology.This alloy has the potential to replace Ti-6Al-4V in automotive and aerospace applications,given its superior mechanical properties,which are approximately 10％higher in terms of ultimate tensile strength(UTS)and yield strength after appropri-ate heat treatment.In as-built conditions,the alloy is characterized by the presence of soft orthorhombic α"martensite,necessitating a postprocessing heat treatment to decompose this phase and enhance the mechanical properties of the alloy.Usually,PBFed Ti6246 com-ponents undergo an annealing process that transforms the α"martensite into an α-β lamellar microstructure.The primary objective of this research was to develop a solution treatment and aging(STA)heat treatment tailored to the unique microstructure produced by the addit-ive manufacturing process to achieve an ultrafine bilamellar microstructure reinforced by precipitation hardening.This study investigated the effects of various solution temperatures in the α-β field(ranging from 800 to 875℃),cooling media(air and water),and aging time to determine the optimal heat treatment parameters for achieving the desired bilamellar microstructure.For each heat treatment condition,different α-β microstructures were found,varying in terms of the α/β ratio and the size of the primary α-phase lamellae.Particular atten-tion was given to how these factors were influenced by increases in solution temperature and how microhardness correlated with the percentage of the metastable β phase present after quenching.Tensile tests were performed on samples subjected to the most promising heat treatment parameters.A comparison with literature data revealed that the optimized STA treatment enhanced hardness and UTS by 13％and 23％,respectively,compared with those of the annealed alloy.Fracture surface analyses were conducted to investigate fracture mechanisms.
查看更多>>摘要：At present,the emerging solid-phase friction-based additive manufacturing technology,including friction rolling additive man-ufacturing(FRAM),can only manufacture simple single-pass components.In this study,multi-layer multi-pass FRAM-deposited alumin-um alloy samples were successfully prepared using a non-shoulder tool head.The material flow behavior and microstructure of the over-lapped zone between adjacent layers and passes during multi-layer multi-pass FRAM deposition were studied using the hybrid 6061 and 5052 aluminum alloys.The results showed that a mechanicalinterlocking structure was formed between the adjacent layers and the adja-cent passes in the overlapped center area.Repeated friction and rolling of the tool head led to different degrees of lateral flow and plastic deformation of the materials in the overlapped zone,which made the recrystallization degree in the left and right edge zones of the over-lapped zone the highest,followed by the overlapped center zone and the non-overlapped zone.The tensile strength of the overlapped zone exceeded 90％of that of the single-pass deposition sample.It is proved that although there are uneven grooves on the surface of the over-lapping area during multi-layer and multi-pass deposition,they can be filled by the flow of materials during the deposition of the next lay-er,thus ensuring the dense microstructure and excellent mechanical properties of the overlapping area.The multi-layer multi-pass FRAM deposition overcomes the limitation of deposition width and lays the foundation for the future deposition of large-scale high-performance components.
查看更多>>摘要：The local structure and thermophysical behavior of Mg-La liquid alloys were in-depth understood using deep potential mo-lecular dynamic(DPMD)simulation driven via machine learning to promote the development of Mg-La alloys.The robustness of the trained deep potential(DP)model was thoroughly evaluated through several aspects,including root-mean-square errors(RMSEs),energy and force data,and structural information comparison results;the results indicate the carefully trained DP model is reliable.The compon-ent and temperature dependence of the local structure in the Mg-La liquid alloy was analyzed.The effect of Mg content in the system on the first coordination shell of the atomic pairs is the same as that of temperature.The pre-peak demonstrated in the structure factor indic-ates the presence of a medium-range ordered structure in the Mg-La liquid alloy,which is particularly pronounced in the 80at％Mg sys-tem and disappears at elevated temperatures.The density,self-diffusion coefficient,and shear viscosity for the Mg-La liquid alloy were predicted via DPMD simulation,the evolution patterns with Mg content and temperature were subsequently discussed,and a database was established accordingly.Finally,the mixing enthalpy and elemental activity of the Mg-La liquid alloy at 1200 K were reliably evaluated,which provides new guidance for related studies.
查看更多>>摘要：We have developed a superhydrophobic and corrosion-resistant LDH-W/PFDTMS composite coating on the surface of Mg al-loy.This composite comprised a tungstate-intercalated(LDH-W)underlayer that was grown at low temperature(relative to hydrothermal reaction conditions)under atmospheric pressure and an outer polysiloxane layer created from a solution containing perfluorodecyltri-methoxysilane(PFDTMS)using a simple immersion method.The successful intercalation of tungstate into the LDH phase and the fol-lowing formation of the polysiloxane layer were confirmed through X-ray diffraction(XRD),Fourier transform infrared(FTIR)spectro-scopy,and X-ray photoelectron spectroscopy(XPS).The corrosion resistance of the LDH-W film,both before and after the PFDTMS modification,was evaluated using electrochemical impedance spectroscopy(EIS),Tafel curves,and immersion experiments.The results showed that Mg coated with LDH-W/PFDTMS exhibited significantly enhanced corrosion protection compared to the unmodified LDH-W film,with no apparent signs of corrosion after exposure to 3.5wt％NaCl solution for 15 d.Furthermore,the LDH-W/PFDTMS coat-ing demonstrated superior superhydrophobicity and self-cleaning properties against water and several common beverages,as confirmed by static contact angle and water-repellency tests.These results offer valuable insights into preparing superhydrophobic and corrosion-res-istant LDH-based composite coatings on Mg alloy surfaces under relatively mild reaction conditions.
查看更多>>摘要：Carbon materials are widely recognized as highly promising electrode materials for various energy storage system applications.Coal tar residues(CTR),as a type of carbon-rich solid waste with high value-added utilization,are crucially important for the develop-ment of a more sustainable world.In this study,we employed a straightforward direct carbonization method within the temperature range of 700-1000℃ to convert the worthless solid waste CTR into economically valuable carbon materials as anodes for potassium-ion batter-ies(PIBs).The effect of carbonization temperature on the microstructure and the potassium ions storage properties of CTR-derived car-bons(CTRCs)were systematically explored by structural and morphological characterization,alongside electrochemical performances as-sessment.Based on the co-regulation between the turbine layers,crystal structure,pore structure,functional groups,and electrical con-ductivity of CTR-derived carbon carbonized at 900℃(CTRC-900H),the electrode material with high reversible capacity of 265.6 mAh•g-1 at 50 mA•g-1,a desirable cycling stability with 93.8％capacity retention even after 100 cycles,and the remarkable rate perform-ance for PIBs were obtained.Furthermore,cyclic voltammetry(CV)at different scan rates and galvanostatic intermittent titration tech-nique(GITT)have been employed to explore the potassium ions storage mechanism and electrochemical kinetics of CTRCs.Results in-dicate that the electrode behavior is predominantly governed by surface-induced capacitive processes,particularly under high current densities,with the potassium storage mechanism characterized by an"adsorption-weak intercalation"mechanism.This work highlights the potential of CTR-based carbon as a promising electrode material category suitable for high-performance PIBs electrodes,while also provides valuable insights into the new avenues for the high value-added utilization of CTR.
查看更多>>摘要：Exploring efficient and nonprecious metal electrocatalysts of oxygen reduction reaction(ORR)and oxygen evolution reaction(OER)is crucial for developing rechargeable zinc-air batteries(ZABs).Herein,an alloying-degree control strategy was employed to fab-ricate nitrogen-doped carbon sphere(NCS)decorated with dual-phase Co/Co7Fe3 heterojunctions(CoFe@NCS).The phase composition of materials has been adjusted by controlling the alloying degree.The optimal CoFe0.08@NCS electrocatalyst displays a half-wave poten-tial of 0.80 V for ORR and an overpotential of 283 mV at 10 mA·cm-2 for OER in an alkaline electrolyte.The intriguing bifunctional electrocatalytic activity and durability is attributed to the hierarchically porous structure and interfacial electron coupling of highly-active Co7Fe3 alloy and metallic Co species.When the CoFe0.08@NCS material is used as air-cathode catalyst of rechargeable liquid-state zinc-air battery(ZAB),the device shows a high peak power-density(157 mW·cm-2)and maintains a stable voltage gap over 150 h,out-performing those of the benchmark(Pt/C+RuO2)-based device.In particular,the as-fabricated solid-state flexible ZAB delivers a reliable compatibility under different bending conditions.Our work provides a promising strategy to develop metal/alloy-based electrocatalysts for the application in renewable energy conversion technologies.
查看更多>>摘要：BiVO4 porous spheres modified by ZnO were designed and synthesized using a facile two-step method.The resulting ZnO/BiVO4 composite catalysts have shown remarkable efficiency as piezoelectric catalysts for degrading Rhodamine B(RhB)under mechanical vibrations,they exhibit superior activity compared to pure ZnO.The 40wt％ZnO/BiVO4 heterojunction composite displayed the highest activity,along with good stability and recyclability.The enhanced piezoelectric catalytic activity can be attributed to the form-ation of an I-scheme heterojunction structure,which can effectively inhibit the electron-hole recombination.Furthermore,hole(h+)and superoxide radical(·O2-)are proved to be the primary active species.Therefore,ZnO/BiVO4 stands as an efficient and stable piezoelectric catalyst with broad potential application in the field of environmental water pollution treatment.
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