Haoxue YangJinshan LiXiangyu PanWilliam Yi Wang...
1-7页
查看更多>>摘要：Precipitation-hardening in fcc-based high-entropy alloys (HEAs) have usually been realized by introducing complex intermetallic compounds.In this study,enhanced strength is ascribed to the existence of L12 precipitates and B2/bcc conjoint phases in the fcc matrix.The nano-size particles in the Al0.5 CoCrFeNi HEA are produced by cold-rolling,followed by intermediate-temperature-annealing at 650 ℃.For L12 ordering,the initial granular structure has transformed into lamella structure and then kept stable when the holding time prolonged to 200 h.The formation of this conjoint B2/bcc driven by the concentration profiles takes place when the diffusion process of elements is sufficient after long-time aging.Based on the microstructure analysis,changes in mechanical properties are associated with the shape,size scale and volume fraction of the precipitates.The peak ultimate tensile stress reaches 1221.5 MPa,1.97 times compared with the as-cast alloy,remaining plasticity of 21.3％.
查看更多>>摘要：High entropy diborides are new categories of ultra-high temperature ceramics,which are believed promising candidates for applications in hypersonic vehicles.However,knowledge on high temperature thermal and mechanical properties of high entropy diborides is still lacking unit now.In this work,variations of thermal and elastic properties of high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 with respect to temperature were predicted by molecular dynamics simulations.Firstly,a deep learning potential for Ti-Zr-Hf-Nb-Ta-B diboride system was fitted with its prediction error in energy and force respectively being 9.2 meV/atom and 208 meV/(A),in comparison with first-principles calculations.Then,temperature dependent lattice constants,anisotropic thermal expansions,anisotropic phonon thermal conductivities,and elastic properties of high entropy (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 from 0 ℃ to 2400 ℃ were evaluated,where the predicted room temperature values agree well with experimental measurements.In addition,intrinsic lattice distortions of (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 were analyzed by displacements of atoms from their ideal positions,which are in an order of 10-3 (A) and one order of magnitude smaller than those in (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)C.It indicates that lattice distortions in (Ti0.2Zr0.2Hf0.2Nb0.2Ta0.2)B2 is not so severe as expected.With the new paradigm of machine learning potential,deep insight into high entropy materials can be achieved in the future,since the chemical and structural complexly in high entropy materials can be well handled by machine learning potential.
查看更多>>摘要：Influences of Sn and Y on the microstructure,mechanical properties,and corrosion behavior of as-cast Mg-5Li-3Al-2Zn (LAZ532) alloy were investigated.The addition of Sn and Y refines grains and results in the formation of Mg2Sn and Al2Y phases,thus improving the mechanical properties of alloy by second phase strengthening and grain refinement strengthening.As-cast LAZ532 alloy shows typical filiform corrosion morphology,and the addition of Sn and Y does not change the corrosion mode of alloy.Ascast LAZ532-0.8Sn-1.2Y alloy shows excellent mechanical properties with yield strength of 166.2 MPa,ultimate tensile strength of 228.6 MPa and elongation of 14.8 ％,and exhibits the best corrosion resistance with the smallest corrosion current density and the lowest anodic dissolution rate.
查看更多>>摘要：A multicomponent (TiZrHfNbTaMo)C ceramic has been fabricated by pressureless sintering at temperatures from 2100 ℃ to 2500 ℃,using an equimolar multicomponent carbide powder synthesized by carbothermal reduction as the starting material.Influence of sintering temperature on densification,microstructure and mechanical properties of the ceramics was investigated.The relative density increases with increasing sintering temperature,and a nearly fully dense sample is achieved by pressureless sintering at 2500 ℃.Average grain size increases from 3.7 to 15.2 μm with increasing sintering temperature from 2300 to 2500 ℃.The (TiZrHfNbTaMo)C ceramic sintered at 2400 ℃ exhibits a single phase fcc structure with homogeneous chemical composition,an average grain size of 7.0 μm and a relative density of 96.5％,while its measured hardness is 33.2 GPa at 100 mN and 23.2 GPa at 9.8 N.
查看更多>>摘要：The CrFeCoNi high-entropy alloy (HEA) exhibits excellent mechanical properties at lower temperatures due to its low stacking-fault energy,however,its medium-and high-temperature strengths are still insufficient.In consideration of the potential diversified applications,more strengthening approaches except for the previously proposed L12 phase hardening deserve further exploration due to its rapid coarsening tendency at high temperatures.Here,we achieved significant high-temperature strengthening of the cast CrFeCoNi HEA by in-situ precipitation of highly thermostable carbides.Alloys with 0.5 at.％ and 1 at.％ niobium and carbon were prepared by simple casting processes,i.e.drop cast,solute solution and aging.A highly thermostable microstructure was formed,which comprises very coarse grains accompanied with extensive thermostable carbide precipitates embedded,including submicrometer coherent NbC particles in grain interiors and intergranular coherent M23C6 carbides.This high thermostability of microstructure,which is beneficial for the high-temperature loading,is ascribed to the synergy of lacking growth driving force and Zenner pinning effect by the carbides.Tensile properties tested at 673,873 and 1073 K show that the yield strength and ultimate tensile strength are significantly increased by Nb/C doping,along with the elongation escalation at higher temperatures.The strengthening is mainly due to the precipitation hardening of carbide particles.
查看更多>>摘要：In this work,the Invar 36 alloys were manufactured using cold spray (CS) additive manufacturing technique.The systematic investigations were made on the microstructural evolution,thermal expansion and mechanical properties under as-sprayed (AS) and heat-treated (HT) conditions.XRD (X-ray diffraction)and ICP-AES (inductively coupled plasma atomic emission spectroscopy) analyses show that no phase transformation,oxidation,nor element content change have occurred.The X-ray computed tomography (XCT) exhibited a near fully dense structure with a porosity of 0.025％ in the helium-produced sample under as-sprayed condition,whereas the nitrogen-produced samples produced at 5 MPa and 800 ℃ show more irregular pore defects.He-AS sample shows a more prominent grain refinement than that of nitrogen samples due to the more extensive plastic deformation.The post heat-treatment exhibited a promoted grain growth,inter-particle diffusion,as well as the formation of annealing twins.Between 25 ℃ and 200 ℃,the nitrogen samples possessed lower CTE (coefficient of thermal expansion) values (1.53 × 10-6/℃) compared with those produced by casting and laser additive manufacturing.The He-AS samples exhibited a noticeable negative CTE value between 25 ℃ and 200 ℃,which may due to the significant compressive residual stress (-272 MPa) compensating its displacement with temperature increase during CTE test.The N2-HT and He-HT Invar 36 samples present a notable balance between strength and ductility.In conclusion,the CS technique can be considered as a potential method to produce the Invar 36 component with high thermal and mechanical performance.
查看更多>>摘要：Precipitation-hardened high entropy alloys (HEAs) with carefully tuned compositions have shown excellent mechanical properties,demonstrating great potential for engineering applications.However,due to the lack of precise multiple phase diagrams,the composition design of multi-principal-component HEAs still inevitably relies on the extremely time-consuming trial-and-error approach.The present study,on the basis of powerful composition quantification ability of atom probe tomography (APT) technology,proposed a framework to guide the quantitative design of precipitation-hardened HEAs.In this framework,the elemental partitioning was used as a crucial route to avoid the thermodynamic challenge of designing precipitation-hardened HEAs.As a case study,the role of Ti/Al ratio in the design of γ-γ'HEAs was predicted through the proposed framework and then validated by experimental studies.The framework predicted that when the total content of Ti and Al is fixed,a higher Ti/Al ratio makes γ-γ'HEA stronger.APT and mechanical results agreed well with these predictions and validated the feasibility of the framework.These findings provided a new route to design the precipitation-hardened alloys and a deeper insight into the design of γ-γ'HEA.
查看更多>>摘要：As one of the most delicate bioprocesses in nature,biosilicification is closely related to biosilica with various morphologies,and has provided abundant inspiration to materials synthesis.In the present study,to explore the biosilica formation process and fabricate silica with an exquisite microstructure for lithiumion battery (LIB) electrodes,a bacterial phage (M13) is used as a biotemplate to synthesize silica with diverse morphologies: cylinders,hexagonal prisms,assemblies of smaller cylinders and nanowires.A facile ethanol bath method is conducted to coat the nanowires with nitrogen-containing carbon and carbon-coated Si02 nanowires with mesochannels (C@msSiO2NWs) are first used as anode materials for LIBs.Attributed to the uniform carbon coating and parallel mesochannel structure,the electronic conductivity and capacity to accommodate volume variations were significantly improved.In the electrochemical performance test,the composites calcined at 750 ℃ (C@msSiO2NWs-750) show an impressive capacity of 653 mA h g-1 at a current density of 500 mA g-1 and stability (1000 cycles).In view of the electrochemical test outcomes,the preparation of a sophisticated structure with an outstanding potential is easily achieved via a biomimetic strategy.
查看更多>>摘要：Ferromagnetic high damping (FHA) alloys with a wide temperature range from-150 ℃ to 300 ℃ have unique application value in extreme environments.In the present work,the damping behaviors of Fe21Ga-xLa (x =0.12 wt.％,0.24 wt.％,0.47 wt.％,1.18 wt.％,and 2.33 wt.％La) alloys have been studied in detail,and a new phenomenoiogical model has been proposed.With the increase of La content,the Laves phase (LaGa2) in the matrix increases gradually,and the resistance opposing the domain movement increases as well.Combined with the results of synchrotron radiation X-ray diffraction,neutron diffraction,and magnetic domain observation,the resistance mainly comes from three parts: the average stress related to the lattice distortion of the matrix,the average stress related to the increasing area energy of domain walls (DWs),and the average stress related to the increasing demagnetization energy induced by the Laves phase.Different from the traditional method of reducing internal stress through annealing to improve the damping capacity,the proper internal stress barriers are necessary to Barkhausen jumps to dissipate energy.Therefore,proper doping to balance resistance and mobility of DWs is a reliable way to improve damping capacity.Meanwhile,for Fe-Al and Fe-Cr based Alloys,the new model also has a good fitting effect.This study provides a theoretical and experimental reference for improving the functional properties of ferromagnetic alloys.
查看更多>>摘要：This work investigated the evolution of multiphase microstructure and impact fracture behavior of medium carbon high silicon high strength steel subjected to the austempering treatment at 240,360,and 400 ℃.The results show that martensite,bainite,and retained austenite (RA) are the main microstructural phases.The austempering treatments at 360 and 400 ℃ caused the formation of carbon-poor ferrite in the matrix,and the transformation of ultrafine bainite into coarse lath bainite and granular bainite,respectively.Thick filmy RA was distributed between bainite laths.The polygonal martensiteaustenite islands and blocky RA formed along the grain boundaries.The average carbon concentration in the matrix decreased with the temperature increase,while the impact toughness initially increased and then dropped with temperature.The quasi-cleavage brittle fracture dominated the impact fracture mechanism of the sample austempered at 240 ℃ by forming tearing surfaces and tearing steps.The microcracks disappeared in the RA on the prior austenite grain boundaries.On the other side,the fracture surface of the sample austempered at 360 ℃ exhibited ductile fracture with deep dimples and brittle fracture with cleavage river patterns.The polygonal martensite-austenite islands or blocky RA constrained the microcracks.After austempered at 400 ℃,the brittle fracture was dominant,showing river patterns,and the microcracks propagated through the granular bainite without any resistance.
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