Counter-gravity casting(CGC)is a widely adopted material processing technique in metals due to its notable benefits,including enhanced filling behavior,reduced defect occurrence,and elevated mechani-cal properties.It ...Counter-gravity casting(CGC)is a widely adopted material processing technique in metals due to its notable benefits,including enhanced filling behavior,reduced defect occurrence,and elevated mechani-cal properties.It plays a pivotal role in fabricating intricate,high-quality components.After its inception in the early 1900s,various CGC processes have emerged,such as low-pressure,counter-pressure,vac-uum suction,and adjusted pressure casting,which are explored in this discourse with an eye toward further advancements.Despite CGC’s superiority over traditional gravity casting and other manufacturing methodologies,specific issues and constraints persist within CGC.This paper endeavors to provide a com-prehensive overview of the historical progression of CGC,its recent developments,and the associated re-search aspects,encompassing topics like filling processes,solidification,microstructural transformations,and the resultant mechanical properties of the fabricated products.Additionally,this paper offers insights into the future challenges and opportunities of CGC.展开更多
The generation of defects,such as cracks and pores,presents significant challenges for high-strength met-als and alloys fabricated by the quick-emerging additive manufacturing technology,and subsequent post-processing...The generation of defects,such as cracks and pores,presents significant challenges for high-strength met-als and alloys fabricated by the quick-emerging additive manufacturing technology,and subsequent post-processing treatments are often necessary before their practical applications.In this work,a novel heat treatment approach,involving a pre-softening treatment before hot isostatic pressing(HIP),is developed to facilitate the crack-healing in René142 superalloy produced through laser powder bed fusion.Results demonstrate that René142 alloy exhibits a propensity for severe cracking across a wide range of printing parameters,primarily in the form of solidification cracks and liquation cracks.These cracks are formed mainly due to a wide solidification range,the presence of a liquid film,and the concentration of resid-ual stress.The pre-softening solution heat treatment significantly reduces dislocation density and resid-ual stress levels,and the subsequent HIP together leads to a defect-free,dense structure for René142 superalloy.Consequently,the René142 alloy processed by the pre-softening HIP treatment achieves an excellent combination of yield strength(850 MPa),ultimate tensile strength(1227 MPa),and elongation(13.7%),with pseudo-equiaxed grains(120-150μm)and squareγ'precipitates(approximately 540 nm).These findings provide valuable insights for exploring crack elimination methods in other nickel-based superalloys fabricated through additive manufacturing.展开更多
The variations of coarse intermetallic particles in hot-extruded 7055 aluminum alloys with 0.041 wt%Fe and 0.024 wt%Si increasing to 0.272 wt%Fe and 0.134 wt%Si were investigated.The particle stimulated nucleation(PSN...The variations of coarse intermetallic particles in hot-extruded 7055 aluminum alloys with 0.041 wt%Fe and 0.024 wt%Si increasing to 0.272 wt%Fe and 0.134 wt%Si were investigated.The particle stimulated nucleation(PSN)behaviors for different kind of coarse particles were detailly analyzed by EBSD.Moreover,the effect of PSN responding to Fe and Si contents on recrystallization and tensile properties of 7055 alloys was evaluated.With increasing Fe and Si contents,the size and number density of coarseη/S particles are reduced,while the number densities of coarse Al7Cu2 Fe and Mg2Si particles are both increased and the coarse Al7Cu2 Fe particles transform from rod-like to irregular.More PSN recrystallized grains with predominant orientations deviated from the extruded fiber textures are stimulated by the irregular Al7Cu2 Fe and Mg2Si particles,because a higher degree of local non-uniform deformation is produced.The rod-like Al7Cu2 Fe particles cause the greatest degree of local non-uniform deformation owing to the largest aspect ratio,but the shape also restricts the area of particle deformation zone(PDZ)resulting in fewer PSN recrystallized grains.The irregularη/S particles give rise to the lowest degree of local non-uniform deformation and fewest PSN recrystallized grains with the major orientations close to the extruded fiber textures.Consequently,despite the number and size of coarseη/S particles are reduced,the proportion of high angle grain boundaries(HAGBs)is increased and the extruded fiber textures are weakened with Fe and Si contents increasing,because of the increased Al7Cu2 Fe and Mg2Si particles.The strength is slightly declined by the weakened<111>//ED(extrusion direction)fiber texture,while the elongation is reduced for a larger number of coarse particles and more HAGBs with higher Fe and Si contents.展开更多
Additively manufactured high-entropy alloys generally suffer from low strength and/or poor ductility.In this work,by leveraging the good castability of eutectic high entropy alloys and high cooling rate of selective l...Additively manufactured high-entropy alloys generally suffer from low strength and/or poor ductility.In this work,by leveraging the good castability of eutectic high entropy alloys and high cooling rate of selective laser melting(SLM),we report a nearly fully dense and crack-free as-SLM AlCoCrFeNi_(2.1) eutectic high entropy alloy with an exceptional strength-ductility synergy,showing an ultrahigh yield strength of 982.1±35.2 MPa and an ultimate tensile strength of 1322.8±54.9 MPa together with an elongation to fracture of 12.3±0.5%.Such strength-ductility enhancement is owing to the heterogeneous eutectic microstructure consisting of the columnar,equiaxed,and“L-shape”cells with much refined sizes down to nanoscales.The morphology of cells in the transition zone is related to the misorientation between the growth direction of adjacent layers.This heterogeneous eutectic microstructure is the result of the graingrowth behavior dominated by the mechanisms of the epitaxial growth and growth of heterogeneous nuclei in SLM.Our current results provide a new methodology for the future design of ultrahigh-strength and ductile SLM-fabricated metallic materials including HEAs,and other printable alloys for various structural applications.展开更多
The twinning-induced plasticity(TWIP)effect has been widely utilized in austenite steels,β-Ti alloys,and recently developed face-centered-cubic(FCC)high-entropy alloys(HEAs)to simultaneously enhance the tensile stren...The twinning-induced plasticity(TWIP)effect has been widely utilized in austenite steels,β-Ti alloys,and recently developed face-centered-cubic(FCC)high-entropy alloys(HEAs)to simultaneously enhance the tensile strength and ductility.In this study,for the first time,the TWIP effect through hierarchical{332}<113>mechanical twinning has been successfully engineered into the TiZrHfNb refractory HEAs by decreasing temperature and tailoring the content of Nb to destabilize the BCC phase.At cryogenic tem-perature,the comprehensive hierarchical{332}<113>mechanical twins are activated in TiZrHfNb_(0.5) alloy from micro-to nanoscale and progressively segment the BCC grains into nano-scale islands during de-formation,ensuring sustainable strain hardening capability and eventually achieving a substantial 35%uniform tensile elongation.In addition,at 77 K,the tensile strength and uniform elongation of TiZrHfNbx alloys can further be adjusted by a moderate increase of Nb.The results above shed new light on the de-velopment of high-performance refractory HEAs with a high and adjustable strength and ductility com-bination down to the cryogenic temperature.展开更多
Mg-Al-Ni alloys were prepared by powder metallurgy, and their microstructure and elevated temperature mechanical properties were investigated. Results indicate that, in addition to α-Mg matrix, both coarse Al;Ni;part...Mg-Al-Ni alloys were prepared by powder metallurgy, and their microstructure and elevated temperature mechanical properties were investigated. Results indicate that, in addition to α-Mg matrix, both coarse Al;Ni;particles and fine Al Ni nano-particles exist in the Mg-Al-Ni alloys. The strength at 150?C is improved with the increase in Ni content. Mg-18.3Al-8Ni alloy possesses a compressive strength of234.7 MPa and a yield strength of 146.5 MPa. Plasticity is also improved with a low concentration of Ni. Mg-11.3Al-2Ni alloy possesses a compression ratio of 17.3%. The phases of Al;Ni;and Al Ni in the alloys block the movements of grain boundaries and dislocations during the deformation at elevated temperature. The existence of Al Ni phase provides a non-basal slip system, leading to the improvement in plasticity. Finally, the formation mechanism of Al-Ni phases in the process is discussed with thermodynamics and kinetics.展开更多
An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported.The screw dislocation glide,deformation twinning,and dislocation accumulation induced kink bands...An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported.The screw dislocation glide,deformation twinning,and dislocation accumulation induced kink bands are identified as three deformation mechanisms that contribute to a large elongation above 20%.The{112}<111>twins are activated at the beginning of the yield stage accompanied by sudden stress-drop and pronounced acoustic emission.Dislocations dominate subsequent tensile deformation,and the prevalent multiplanar dislocation slip promotes the formation of complex dislocation configurations(e.g.,debris,dipoles,and loops)and dense dislocation networks.The twin bands and kink bands can further impede the dislocation motion meanwhile effectively alleviate stress concentration.The synergistic activation of these deformation mechanisms provides new opportunities to design ductile refractory medium-and high-entropy alloys.展开更多
Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated...Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated. Results show that, during ARB process, the evolution of deformation mechanism oft Mg-5Li-1Al alloy is as follows： twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization （DRX）. The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.展开更多
With the development of aerospace and transportation,high-strength structural materials manufactured by additive manufacturing techniques get more attention,which allows the production of counterparts with complex str...With the development of aerospace and transportation,high-strength structural materials manufactured by additive manufacturing techniques get more attention,which allows the production of counterparts with complex structures.This work investigates Al-added CoCrFeMnNi high-entropy alloys(Al-HEAs)pre-pared by laser powder bed fusion(PBF-LB),adding 4.4 wt.%Al reducing approximately 7%density.The contribution of post-heat-treatment to microstructure,mechanical properties,and corrosion behaviors are explored.Hot cracking along with grain boundaries in the as-built PBF-LB Al-HEAs is determined,which comes from the residual liquid film as a larger solidification temperature range by adding Al.The PBF-LB Al-HEAs mainly consist of a face-centered cubic(FCC)matrix with Al/Ni/Mn decorated dislocation cells therein and a minor body-centered cubic(BCC)phase.Upon 850℃ annealing treatment,massive BCC phases(ordered NiAl and disordered Cr-rich precipitates)generate at the dislocation cell/grain bound-aries and the dislocation cells are still retained.However,the volume fraction of BCC phases and the dislocation cells vanish after 1150℃ solution treatment.As a result,Al-HEA850 shows an over 1000 MPa yield strength with nearly no ductility(<3%);the Al-HEA1150 exhibits considerable strength-ductility properties.Meanwhile,the Al-HEA850 demonstrates the worst pitting corrosion resistance due to the preferential dissolution of the NiAl precipitates in chloride-containing solutions.After comparatively de-liberating the evolution of strength-ductility and localized corrosion,we built a framework about the effects of the heat treatment on the mechanical property and degradation behavior in additively manu-factured Al-added high-strength HEAs.展开更多
Heterogeneous structures(HS)materials have the potential to exhibit simultaneous improvement in strength and plasticity due to hetero-deformation-induced hardening(HDI)between multiple grain struc-tures.However,achiev...Heterogeneous structures(HS)materials have the potential to exhibit simultaneous improvement in strength and plasticity due to hetero-deformation-induced hardening(HDI)between multiple grain struc-tures.However,achieving HS in aluminum alloy can be quite challenging.In this study,7000 series alu-minum alloys are investigated by incorporating rare earth element Y to develop a dual-phase structure containing Al_(8)Cu_(4)Y and Al_(3)(Y,Zr)phases.And a heterogeneous lamella structure(HLS)is formed through the synergistic effect of Al_(8)Cu_(4)Y which includes dynamic recrystallization nucleation during deformation,and Al_(3)(Y,Zr)which hinders the growth of recrystallized grain by means of pinning dislocations and sub-grain boundaries.Substructures such as precipitates and nanocrystals are incorporated during the fabri-cation of HS,allowing for precise control over the volume fraction of fine grains by adjusting the ratio of two-scale second phases.When Y content reaches 0.3%,the 7Y55-2/heterogeneous lamella structure(HLS)samples exhibit a fine grain volume fraction of 76.5 vol.%,a tensile strength of 695 MPa,and an elon-gation of 16.6%.The alloy contains a large number of dislocations that preferentially induce the growth ofη’phases along specific directions,thereby promoting their development.The multi-coupling effect and composite strengthening mechanisms in the“heterostructure-dislocation-precipitate”microstructure contribute to the intrinsic excellent strength and plasticity of the alloy.This study tackles the challenge of inverted strength and plasticity observed in Al-Zn-Mg-Cu-Zr alloys,offering novel insights that pave the way for further applications of heterogeneous materials.展开更多
Aluminum-ion batteries(AIBs)have been highlighted as a potential alternative to lithium-ion batteries for large-scale energy storage due to the abundant reserve,light weight,low cost,and good safety of Al.However,the ...Aluminum-ion batteries(AIBs)have been highlighted as a potential alternative to lithium-ion batteries for large-scale energy storage due to the abundant reserve,light weight,low cost,and good safety of Al.However,the development of AIBs faces challenges due to the usage of AlCl_(3)-based ionic liquid electrolytes,which are expensive,corrosive,and sensitive to humidity.Here,we develop a low-cost,non-corrosive,and air-stable hydrated eutectic electrolyte composed of aluminum perchlorate nonahydrate and methylurea(MU)ligand.Through optimizing the molar ratio to achieve the unique solvation structure,the formed Al(ClO_4)_(3)·9H_(2)O/MU hydrated deep eutectic electrolyte(AMHEE)with an average coordination number of 2.4 can facilely realize stable and reversible deposition/stripping of Al.When combining with vanadium oxide nanorods positive electrode,the Al-ion full battery delivers a high discharge capacity of 320 mAh g^(-1)with good capacity retention.The unique solvation structure with a low desolvation energy of the AMHEE enables Al^(3+)insertion/extraction during charge/discharge processes,which is evidenced by in situ synchrotron radiation X-ray diffraction.This work opens a new pathway of developing low-cost,safe,environmentally friendly and high-performance electrolytes for practical and sustainable AIBs.展开更多
In order to improve the ductility of commercial WE43 alloy and reduce its cost,a Mg-3Y-2Gd-1Nd-0.4Zr alloy with a low amount of rare earths was developed and prepared by sand casting with a differential pressure casti...In order to improve the ductility of commercial WE43 alloy and reduce its cost,a Mg-3Y-2Gd-1Nd-0.4Zr alloy with a low amount of rare earths was developed and prepared by sand casting with a differential pressure casting system.Its microstructure,mechanical properties and fracture behaviors in the as-cast,solution-treated and as-aged states were evaluated.It is found that the aged alloy exhibited excellent comprehensive mechanical properties owing to the fine dense plate-shapedβ'precipitates formed on prismatic habits during aging at 200℃for 192 hrs after solution-treated at 500℃for 24 hrs.Its ultimate tensile strength,yield strength,and elongation at ambient temperature reach to 319±10 MPa,202±2 MPa and 8.7±0.3%as well as 230±4 MPa,155±1 MPa and 16.0±0.5%at 250℃.The fracture mode of as-aged alloy was transferred from cleavage at room temperature to quasi-cleavage and ductile fracture at the test temperature 300℃.The properties of large-scale components fabricated using the developed Mg-3Y-2Gd-1Nd-0.4Zr alloy are better than those of commercial WE43 alloy,suggesting that the new developed alloy is a good candidate to fabricate the large complex thin-walled components.展开更多
Thermally stable nano-size ceramic particles are the preferred reinforcements for superalloys as they improve the alloys'microstructural stability and high-temperature properties.In this work,very dense and crack-...Thermally stable nano-size ceramic particles are the preferred reinforcements for superalloys as they improve the alloys'microstructural stability and high-temperature properties.In this work,very dense and crack-free carbidereinforced GTD222(nickel-based superalloy)composites were prepared via selective laser melting(SLM).The distribution of TiC nanoparticles presents a three-dimensional(3D)network structure in the SLMed TiC/GTD222 composite.Mechanical testing revealed that the SLMed TiC/GTD222 composite has superior strength(UTS?1320 MPa,YS?1100 MPa)compared to the SLMed GTD222 superalloy.The GTD22 alloy reinforced with carbide nanoparticles’distinctive microstructure and its excellent mechanical properties for is discussed.展开更多
During solidifications of immiscible alloys,the motion of droplets at the solid/liquid(S/L)interface is gen-erally driven by dragging force,gravity force,repulsion force of interface,and thermal-solutal Marangoni forc...During solidifications of immiscible alloys,the motion of droplets at the solid/liquid(S/L)interface is gen-erally driven by dragging force,gravity force,repulsion force of interface,and thermal-solutal Marangoni force,However,there is few in situ study investigating kinetics behavior to analyze the forces on droplets.The mechanism of droplet motion remains unclear due to the unavailability or uncertainty of the effect of convection and solutal Marangoni force on droplet behavior.In this study,directional solidification of im-miscible Al-Bi alloy was observed via synchrotron radiography,and the horizontal oscillation of droplets at S/L interface was detected for the first time.Forces,especially solutal Marangoni force,were calcu-lated based on the in situ measured radius of droplets and thermal-solutal gradients.The experimental results cannot be reasonably explained by the previous analysis model which neglects melt convection.The non-negligible effect of flow on droplet motion was demonstrated,and the force balance of droplet both vertically and horizontally can be obtained considering a lift force of 6.39 × 10^(-9) N and a modified solute-related parameter dσ/dc of 0.45-0.65 J m^(-2),respectively.展开更多
Titanium diboride(TiB_(2))is an effective grain refiner of Al alloys in the industry that facilitates casting processes by forming uniformly refined microstructures.Although our understanding of the underlying refinem...Titanium diboride(TiB_(2))is an effective grain refiner of Al alloys in the industry that facilitates casting processes by forming uniformly refined microstructures.Although our understanding of the underlying refinement mechanisms has advanced,the atomic kinetics of heterogeneous nucleation of Al on TiB2 remains unknown.Here,we report atomic-scale observations of the heterogeneous nucleation and growth kinetics of Al on self-formed TiB_(2) particles by in situ heating of undercooled Al-5Ti-1B films.We demonstrate that an ordered Al monolayer forms on the Ti-terminated{0001}TiB_(2) surface;then,the surrounding Al atoms are initiated to form an island-shaped Al nucleus with face-centered cubic{111}stacking without the assistance of a Ti-rich buffer layer.The interfacial lattice mismatch between{111}Al and{0001}TiB_(2) causes remarkable out-of-plane strain that decreases gradually with Al nucleus layers increasing to 6 atomic layers.The elastic strain energy originating from this interfacial strain increases the free energy of the Al/TiB2 heterostructure,hence impeding the rapid growth of the Al nucleus.We found that TiB2 particles stabilize the Al nuclei rather than activating their free growth into grains when the experimental undercoolingΔT is lower than the onset undercoolingΔT fg in Greer's free growth model.Our findings provide an atomic-scale physical image of the heterogeneous nucleation and growth mechanisms of Al with inoculator participation and elucidate the strain-dependent growth kinetics of Al nuclei.展开更多
Grain refinement of Al alloys inoculated by rare earth elements,such as Sc,has been extensively acknowledged,while the practical behavior of how inoculant Al_(3)Sc particles affect the refinement in solidification has...Grain refinement of Al alloys inoculated by rare earth elements,such as Sc,has been extensively acknowledged,while the practical behavior of how inoculant Al_(3)Sc particles affect the refinement in solidification has not been clarified due to the non-transparency of the solidification process.Here,the microstructural evolution of primary Al_(3)Sc particles andα-Al grains in Al-10 wt.%Cu alloy solidifications with 0.2 wt.%,0.6 wt.%,and 1.0 wt.%Sc additions was investigated by in situ synchrotron X-ray radiography.The detailed mechanisms of curve motion of grains(CMG)and melt convection were revealed.The efficient grains nucleation,uniformly scattered small initial grains,and long duration of melt convection contributed to the best refinement in the 0.6 wt.%Sc addition sample.This work provides a deep insight into grain refinement in solidification with Sc addition,which will enlighten the composition design and casting process of Al alloys inoculated by rare earth elements.展开更多
Ni Co Cr-based multi-component alloys have drawn much attention due to their exceptional ductility and strain hardening capacity.However,insufficient strength-ductility synergy of NiCoCr alloy has always been an issue...Ni Co Cr-based multi-component alloys have drawn much attention due to their exceptional ductility and strain hardening capacity.However,insufficient strength-ductility synergy of NiCoCr alloy has always been an issue that prevents it from extensive applications.According to our previous research,the precipitation ofγ”phase can significantly improve the strength-ductility synergy of this alloy system at room temperature.In this study,the effects of V addition onγ”phase stability and high-temperature mechanical properties have been explicitly investigated.The results indicate that V addition can stabilize the metastableγ”phase in this alloy system and prevent it from transforming into a stableδphase at grain boundaries upon 650℃aging,resulting in improved mechanical properties at elevated temperatures.The specific strength ofγ”-strengthened multi-component NiCoCr-based alloy can reach up to 86.2 MPa gcmat 650℃,which is higher than those of Ni-based superalloys,IN 939 and Waspaloy.This work provides theoretical guidance for the novel design of γ”-strengthened alloy for high-temperature applications.展开更多
Rechargeable aluminum-sulfur(Al-S)batteries have been considered as a highly potential energy storage system owing to the high theoretical capacity,good safety,abundant natural reserves,and low cost of Al and S.Howeve...Rechargeable aluminum-sulfur(Al-S)batteries have been considered as a highly potential energy storage system owing to the high theoretical capacity,good safety,abundant natural reserves,and low cost of Al and S.However,the research progress of Al-S batteries is limited by the slow kinetics and shuttle effect of soluble polysulfides intermediates.Herein,an interconnected free-standing interlayer of iron sin-gle atoms supported on porous nitrogen-doped carbon nanofibers(FeSAs-NCF)on the separator is developed and used as both catalyst and chemical barrier for Al-S batteries.The atomically dispersed iron active sites(Fe-N_(4))are clearly identified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption near-edge structure.The Al-S battery with the FeSAs-NCF shows an improved specific capacity of 780 mAh g^(−1)and enhanced cycle stability.As evidenced by experimental and theoretical results,the atomically dispersed iron active centers on the separator can chemically adsorb the polysulfides and accelerate reaction kinetics to inhibit the shuttle effect and promote the reversible conversion between aluminum polysulfides,thus improving the electrochemical performance of the Al-S battery.This work provides a new way that can not only promote the conversion of aluminum sulfides but also suppress the shuttle effect in Al-S batteries.展开更多
The microstructure,aging behavior and mechanical properties of cast Mg–3Nd–3Gd–x Zn–0.5Zr(x=0,0.5,0.8,1 wt%)alloys are investigated in this work.Zn–Zr particles with different morphologies form during solution tr...The microstructure,aging behavior and mechanical properties of cast Mg–3Nd–3Gd–x Zn–0.5Zr(x=0,0.5,0.8,1 wt%)alloys are investigated in this work.Zn–Zr particles with different morphologies form during solution treatment due to the additions of Zn.As the Zn content increases,the number density of Zn–Zr particles also increases.Microstructural comparisons of peak-aged studied alloys indicate that varying Zn additions could profoundly influence the competitive precipitation behavior.In the peak-aged Zn-free alloy,β′′phases are the key strengthening precipitates.When 0.5 wt%Zn is added,besidesβ′′precipitates,additional fineβ_(1)precipitates form.With the addition of 0.8 wt%Zn,the peak-aged 0.8Zn alloy is characterized by predominantly prismaticβ_(1)and scanty basal precipitate distributions.The enhanced precipitation ofβ_(1)should be primarily attributable to the presence of increased Zn–Zr dispersoids.When Zn content further increases to 1 wt%,the precipitation of basal precipitates is markedly enhanced.Basal precipitates andβ_(1)phases are the key strengthening precipitates in the peak-aged 1Zn alloy.Tensile tests reveal that the relatively best tensile properties are achieved in the peak-aged alloy with 0.5 wt%Zn addition,whose yield strength,ultimate tensile strength and elongation are 179 MPa,301 MPa and 5.3%,respectively.展开更多
For NiAI intermetallic compound with B2 structure, there is still no calculation combining models of sin- gle and multiple layers while using the same basic set. Furthermore, some recently proposed criteria for brittl...For NiAI intermetallic compound with B2 structure, there is still no calculation combining models of sin- gle and multiple layers while using the same basic set. Furthermore, some recently proposed criteria for brittleness and toughness have not been used to analyze its deformation behavior. Thus, first-principles calculation was applied to comprehensively study the elastic properties, ideal strength, generalized stacking fault energy and surface energy of B2-NiA1 intermetallic compound. The results suggest that calculations based on the current basic set give more accurate lattice parameters and elastic moduli. The Pugh criterion and Cauchy pressure cannot be used to interpret the intrinsic brittleness of NiAI. In comparison, the ductility parameter based on the strain energy under elastic instability and ZCT and Rice criteria based on generalized stacking fault energy and surface energy successfully identify the intrinsic brittleness of the NiA1 intermetallic compound. The reason why [111] slip always occurs in the defor- mation along [100] direction was clarified by examining the critical value for brittle-ductile transition. The results of density of state indicate shear deformation has less impact on structural stability, and the change of charge density difference implies that 〈001〉 shear induces more intensive redistribution of charge density, which is well correlated to the brittleness and deformation behavior of NiAI intermetallic comnound.展开更多
基金supported by the National Sci-ence and Technology Major Project of China(No.J2019-VI-0004-0117)the National Natural Science Foundation of China(Nos.52071205 and 51821001)+2 种基金the Aeronautical Science Fund of China(No.2023Z053057003)the Science and Technology Commission of Shanghai Municipality,China(No.23ZR1428800)the Shanghai Industrial Collaborative Innovation Project(No.XTCX-KJ-2022-41).
文摘Counter-gravity casting(CGC)is a widely adopted material processing technique in metals due to its notable benefits,including enhanced filling behavior,reduced defect occurrence,and elevated mechani-cal properties.It plays a pivotal role in fabricating intricate,high-quality components.After its inception in the early 1900s,various CGC processes have emerged,such as low-pressure,counter-pressure,vac-uum suction,and adjusted pressure casting,which are explored in this discourse with an eye toward further advancements.Despite CGC’s superiority over traditional gravity casting and other manufacturing methodologies,specific issues and constraints persist within CGC.This paper endeavors to provide a com-prehensive overview of the historical progression of CGC,its recent developments,and the associated re-search aspects,encompassing topics like filling processes,solidification,microstructural transformations,and the resultant mechanical properties of the fabricated products.Additionally,this paper offers insights into the future challenges and opportunities of CGC.
基金support of the National Natural Science Foundation of China(Project Nos.52371012 and 52301060).
文摘The generation of defects,such as cracks and pores,presents significant challenges for high-strength met-als and alloys fabricated by the quick-emerging additive manufacturing technology,and subsequent post-processing treatments are often necessary before their practical applications.In this work,a novel heat treatment approach,involving a pre-softening treatment before hot isostatic pressing(HIP),is developed to facilitate the crack-healing in René142 superalloy produced through laser powder bed fusion.Results demonstrate that René142 alloy exhibits a propensity for severe cracking across a wide range of printing parameters,primarily in the form of solidification cracks and liquation cracks.These cracks are formed mainly due to a wide solidification range,the presence of a liquid film,and the concentration of resid-ual stress.The pre-softening solution heat treatment significantly reduces dislocation density and resid-ual stress levels,and the subsequent HIP together leads to a defect-free,dense structure for René142 superalloy.Consequently,the René142 alloy processed by the pre-softening HIP treatment achieves an excellent combination of yield strength(850 MPa),ultimate tensile strength(1227 MPa),and elongation(13.7%),with pseudo-equiaxed grains(120-150μm)and squareγ'precipitates(approximately 540 nm).These findings provide valuable insights for exploring crack elimination methods in other nickel-based superalloys fabricated through additive manufacturing.
基金supported financially by the National Natural Science Foundation of China (No.51821001)
文摘The variations of coarse intermetallic particles in hot-extruded 7055 aluminum alloys with 0.041 wt%Fe and 0.024 wt%Si increasing to 0.272 wt%Fe and 0.134 wt%Si were investigated.The particle stimulated nucleation(PSN)behaviors for different kind of coarse particles were detailly analyzed by EBSD.Moreover,the effect of PSN responding to Fe and Si contents on recrystallization and tensile properties of 7055 alloys was evaluated.With increasing Fe and Si contents,the size and number density of coarseη/S particles are reduced,while the number densities of coarse Al7Cu2 Fe and Mg2Si particles are both increased and the coarse Al7Cu2 Fe particles transform from rod-like to irregular.More PSN recrystallized grains with predominant orientations deviated from the extruded fiber textures are stimulated by the irregular Al7Cu2 Fe and Mg2Si particles,because a higher degree of local non-uniform deformation is produced.The rod-like Al7Cu2 Fe particles cause the greatest degree of local non-uniform deformation owing to the largest aspect ratio,but the shape also restricts the area of particle deformation zone(PDZ)resulting in fewer PSN recrystallized grains.The irregularη/S particles give rise to the lowest degree of local non-uniform deformation and fewest PSN recrystallized grains with the major orientations close to the extruded fiber textures.Consequently,despite the number and size of coarseη/S particles are reduced,the proportion of high angle grain boundaries(HAGBs)is increased and the extruded fiber textures are weakened with Fe and Si contents increasing,because of the increased Al7Cu2 Fe and Mg2Si particles.The strength is slightly declined by the weakened<111>//ED(extrusion direction)fiber texture,while the elongation is reduced for a larger number of coarse particles and more HAGBs with higher Fe and Si contents.
基金Wentao Yan acknowledges the support of A∗STAR AME IRG Grant(No.A20E5c0091)Anping Dong acknowledges the support of the fellowship of China National Postdoctoral Program for Innovative Talents(No.BX20200203)+2 种基金the National Science and Technology Major Project of China(No.J2019-VI-0004-0117)the National Natural Science Foundation of China(No.52071205)Haibin Tang would like to acknowledge startup funds from Nanjing University of Science and Technology(No.JAB25802007/002).
文摘Additively manufactured high-entropy alloys generally suffer from low strength and/or poor ductility.In this work,by leveraging the good castability of eutectic high entropy alloys and high cooling rate of selective laser melting(SLM),we report a nearly fully dense and crack-free as-SLM AlCoCrFeNi_(2.1) eutectic high entropy alloy with an exceptional strength-ductility synergy,showing an ultrahigh yield strength of 982.1±35.2 MPa and an ultimate tensile strength of 1322.8±54.9 MPa together with an elongation to fracture of 12.3±0.5%.Such strength-ductility enhancement is owing to the heterogeneous eutectic microstructure consisting of the columnar,equiaxed,and“L-shape”cells with much refined sizes down to nanoscales.The morphology of cells in the transition zone is related to the misorientation between the growth direction of adjacent layers.This heterogeneous eutectic microstructure is the result of the graingrowth behavior dominated by the mechanisms of the epitaxial growth and growth of heterogeneous nuclei in SLM.Our current results provide a new methodology for the future design of ultrahigh-strength and ductile SLM-fabricated metallic materials including HEAs,and other printable alloys for various structural applications.
基金This work was supported by the National Natural Science Foun-dation of China(Nos.52301163 and 51821001)the National Key R&D Program of China(No.2022YFB3706800)+1 种基金P.K.Liaw very much appreciates the support from(1)the National Science Foun-dation(Nos.DMR-1611180,1809640,and 2226508)(2)the US Army Research Office(Nos.W911NF-13–1–0438 and W911NF-19–2–0049).
文摘The twinning-induced plasticity(TWIP)effect has been widely utilized in austenite steels,β-Ti alloys,and recently developed face-centered-cubic(FCC)high-entropy alloys(HEAs)to simultaneously enhance the tensile strength and ductility.In this study,for the first time,the TWIP effect through hierarchical{332}<113>mechanical twinning has been successfully engineered into the TiZrHfNb refractory HEAs by decreasing temperature and tailoring the content of Nb to destabilize the BCC phase.At cryogenic tem-perature,the comprehensive hierarchical{332}<113>mechanical twins are activated in TiZrHfNb_(0.5) alloy from micro-to nanoscale and progressively segment the BCC grains into nano-scale islands during de-formation,ensuring sustainable strain hardening capability and eventually achieving a substantial 35%uniform tensile elongation.In addition,at 77 K,the tensile strength and uniform elongation of TiZrHfNbx alloys can further be adjusted by a moderate increase of Nb.The results above shed new light on the de-velopment of high-performance refractory HEAs with a high and adjustable strength and ductility com-bination down to the cryogenic temperature.
基金supported by the National Natural Science Foundation of China (No. 51671063)the Research Fund for the Doctoral Program of Higher Education (No. 20132304110006)+1 种基金the Fundamental Research Funds for the Central Universities (No. HEUCF20161016)the Harbin City Application Technology Research and Development Project (Nos. 2015AE4AE005, 2015RQXXJ001, 2016AB2AG013)
文摘Mg-Al-Ni alloys were prepared by powder metallurgy, and their microstructure and elevated temperature mechanical properties were investigated. Results indicate that, in addition to α-Mg matrix, both coarse Al;Ni;particles and fine Al Ni nano-particles exist in the Mg-Al-Ni alloys. The strength at 150?C is improved with the increase in Ni content. Mg-18.3Al-8Ni alloy possesses a compressive strength of234.7 MPa and a yield strength of 146.5 MPa. Plasticity is also improved with a low concentration of Ni. Mg-11.3Al-2Ni alloy possesses a compression ratio of 17.3%. The phases of Al;Ni;and Al Ni in the alloys block the movements of grain boundaries and dislocations during the deformation at elevated temperature. The existence of Al Ni phase provides a non-basal slip system, leading to the improvement in plasticity. Finally, the formation mechanism of Al-Ni phases in the process is discussed with thermodynamics and kinetics.
基金financially supported by the National Natural Science Foundation of China(No.51821001)。
文摘An equiatomic VNbTi medium-entropy alloy with outstanding tensile properties and unique deformation behavior is reported.The screw dislocation glide,deformation twinning,and dislocation accumulation induced kink bands are identified as three deformation mechanisms that contribute to a large elongation above 20%.The{112}<111>twins are activated at the beginning of the yield stage accompanied by sudden stress-drop and pronounced acoustic emission.Dislocations dominate subsequent tensile deformation,and the prevalent multiplanar dislocation slip promotes the formation of complex dislocation configurations(e.g.,debris,dipoles,and loops)and dense dislocation networks.The twin bands and kink bands can further impede the dislocation motion meanwhile effectively alleviate stress concentration.The synergistic activation of these deformation mechanisms provides new opportunities to design ductile refractory medium-and high-entropy alloys.
基金supported by the National Natural Science Foundation of China (51671063)Research Fund for the Doctoral Program of Higher Education (20132304110006)+1 种基金the Fundamental Research Funds for the Central Universities (HEUCF20161016)Harbin City Application Technology Research and Development Project (2015AE4AE005, 2015RQXXJ001, 2016AB2AG013)
文摘Ultrafine-grain and high-strength Mg-SLi-1Al sheets were prepared by accumulative roll bonding （ARB） process. Evolution of microstructure and mechanical properties of ARB-processed Mg-5Li-1Al sheets was investigated. Results show that, during ARB process, the evolution of deformation mechanism oft Mg-5Li-1Al alloy is as follows： twinning deformation, shear deformation, forming macro shear zone, and finally dynamic recrystallization （DRX）. The grain refining mechanism changes from twin DRX to rotation DRX. With the increase in ARB cycles, strength of the Mg-5Li-1Al sheets is enhanced, whilst elongation varies slightly. With the increase in rolling cycles, anisotropy of mechanical properties decreases. It is conclusive that strain hardening and grain refinement dominate the strengthening mechanism of Mg-5Li-1Al alloy.
基金This work is financially supported by the Shanghai Sailing Program(No.21YF1412000)the Natural Science Foundation of Shanghai(No.19ZR1417100).The authors greatly appreciate the access to Thermo-calc software in Prof.Olson’s lab at MIT.
文摘With the development of aerospace and transportation,high-strength structural materials manufactured by additive manufacturing techniques get more attention,which allows the production of counterparts with complex structures.This work investigates Al-added CoCrFeMnNi high-entropy alloys(Al-HEAs)pre-pared by laser powder bed fusion(PBF-LB),adding 4.4 wt.%Al reducing approximately 7%density.The contribution of post-heat-treatment to microstructure,mechanical properties,and corrosion behaviors are explored.Hot cracking along with grain boundaries in the as-built PBF-LB Al-HEAs is determined,which comes from the residual liquid film as a larger solidification temperature range by adding Al.The PBF-LB Al-HEAs mainly consist of a face-centered cubic(FCC)matrix with Al/Ni/Mn decorated dislocation cells therein and a minor body-centered cubic(BCC)phase.Upon 850℃ annealing treatment,massive BCC phases(ordered NiAl and disordered Cr-rich precipitates)generate at the dislocation cell/grain bound-aries and the dislocation cells are still retained.However,the volume fraction of BCC phases and the dislocation cells vanish after 1150℃ solution treatment.As a result,Al-HEA850 shows an over 1000 MPa yield strength with nearly no ductility(<3%);the Al-HEA1150 exhibits considerable strength-ductility properties.Meanwhile,the Al-HEA850 demonstrates the worst pitting corrosion resistance due to the preferential dissolution of the NiAl precipitates in chloride-containing solutions.After comparatively de-liberating the evolution of strength-ductility and localized corrosion,we built a framework about the effects of the heat treatment on the mechanical property and degradation behavior in additively manu-factured Al-added high-strength HEAs.
基金supported by the National Key Research and Development Program of China(No.2023YFB3406800)the National Natural Science Foundation of China(Nos.52271036 and 51971237).
文摘Heterogeneous structures(HS)materials have the potential to exhibit simultaneous improvement in strength and plasticity due to hetero-deformation-induced hardening(HDI)between multiple grain struc-tures.However,achieving HS in aluminum alloy can be quite challenging.In this study,7000 series alu-minum alloys are investigated by incorporating rare earth element Y to develop a dual-phase structure containing Al_(8)Cu_(4)Y and Al_(3)(Y,Zr)phases.And a heterogeneous lamella structure(HLS)is formed through the synergistic effect of Al_(8)Cu_(4)Y which includes dynamic recrystallization nucleation during deformation,and Al_(3)(Y,Zr)which hinders the growth of recrystallized grain by means of pinning dislocations and sub-grain boundaries.Substructures such as precipitates and nanocrystals are incorporated during the fabri-cation of HS,allowing for precise control over the volume fraction of fine grains by adjusting the ratio of two-scale second phases.When Y content reaches 0.3%,the 7Y55-2/heterogeneous lamella structure(HLS)samples exhibit a fine grain volume fraction of 76.5 vol.%,a tensile strength of 695 MPa,and an elon-gation of 16.6%.The alloy contains a large number of dislocations that preferentially induce the growth ofη’phases along specific directions,thereby promoting their development.The multi-coupling effect and composite strengthening mechanisms in the“heterostructure-dislocation-precipitate”microstructure contribute to the intrinsic excellent strength and plasticity of the alloy.This study tackles the challenge of inverted strength and plasticity observed in Al-Zn-Mg-Cu-Zr alloys,offering novel insights that pave the way for further applications of heterogeneous materials.
基金supported by the National Natural Science Foundation of China(52274302)。
文摘Aluminum-ion batteries(AIBs)have been highlighted as a potential alternative to lithium-ion batteries for large-scale energy storage due to the abundant reserve,light weight,low cost,and good safety of Al.However,the development of AIBs faces challenges due to the usage of AlCl_(3)-based ionic liquid electrolytes,which are expensive,corrosive,and sensitive to humidity.Here,we develop a low-cost,non-corrosive,and air-stable hydrated eutectic electrolyte composed of aluminum perchlorate nonahydrate and methylurea(MU)ligand.Through optimizing the molar ratio to achieve the unique solvation structure,the formed Al(ClO_4)_(3)·9H_(2)O/MU hydrated deep eutectic electrolyte(AMHEE)with an average coordination number of 2.4 can facilely realize stable and reversible deposition/stripping of Al.When combining with vanadium oxide nanorods positive electrode,the Al-ion full battery delivers a high discharge capacity of 320 mAh g^(-1)with good capacity retention.The unique solvation structure with a low desolvation energy of the AMHEE enables Al^(3+)insertion/extraction during charge/discharge processes,which is evidenced by in situ synchrotron radiation X-ray diffraction.This work opens a new pathway of developing low-cost,safe,environmentally friendly and high-performance electrolytes for practical and sustainable AIBs.
基金This work was funded by the National Natural Science Foundation of China(No.U2037601 and No.52074183)The authors appreciate Ge Chen,Wenbin Zou as well as Shiwei Wang for preparing the alloys,Wenyu Liu as well as Xuehao Zheng from ZKKF(Beijing)Science&Technology Co.,Ltd for the TEM measurement,Gert Wiese as well as Petra Fischer for SEM and hardness measurement and Yunting Li from the Instrument Analysis Center of Shanghai Jiao Tong University(China)for SEM measurement.Lixiang Yang also gratefully thanks the China Scholarship Council(201906230111)for awarding a fellowship to support his study stay at Helmholtz-Zentrum Geesthacht.
文摘In order to improve the ductility of commercial WE43 alloy and reduce its cost,a Mg-3Y-2Gd-1Nd-0.4Zr alloy with a low amount of rare earths was developed and prepared by sand casting with a differential pressure casting system.Its microstructure,mechanical properties and fracture behaviors in the as-cast,solution-treated and as-aged states were evaluated.It is found that the aged alloy exhibited excellent comprehensive mechanical properties owing to the fine dense plate-shapedβ'precipitates formed on prismatic habits during aging at 200℃for 192 hrs after solution-treated at 500℃for 24 hrs.Its ultimate tensile strength,yield strength,and elongation at ambient temperature reach to 319±10 MPa,202±2 MPa and 8.7±0.3%as well as 230±4 MPa,155±1 MPa and 16.0±0.5%at 250℃.The fracture mode of as-aged alloy was transferred from cleavage at room temperature to quasi-cleavage and ductile fracture at the test temperature 300℃.The properties of large-scale components fabricated using the developed Mg-3Y-2Gd-1Nd-0.4Zr alloy are better than those of commercial WE43 alloy,suggesting that the new developed alloy is a good candidate to fabricate the large complex thin-walled components.
基金The authors grateful acknowledge the financial support of the National Natural Science Foundation of China under Projects No.51871147 and 51704195the China Postdoctoral Science Foundation under Project No.19Z102060057+2 种基金the National Science and Technology Major Project under Project No.2017-VI-0013-0085the Science Fund for Creative Research Groups of the National Natural Science Foundation of China under Project No.51821001the Aviation Power Fund under Project No.6141B090324.
文摘Thermally stable nano-size ceramic particles are the preferred reinforcements for superalloys as they improve the alloys'microstructural stability and high-temperature properties.In this work,very dense and crack-free carbidereinforced GTD222(nickel-based superalloy)composites were prepared via selective laser melting(SLM).The distribution of TiC nanoparticles presents a three-dimensional(3D)network structure in the SLMed TiC/GTD222 composite.Mechanical testing revealed that the SLMed TiC/GTD222 composite has superior strength(UTS?1320 MPa,YS?1100 MPa)compared to the SLMed GTD222 superalloy.The GTD22 alloy reinforced with carbide nanoparticles’distinctive microstructure and its excellent mechanical properties for is discussed.
基金National Natural Science Foundation of China(Nos.52271036 and 51971237)Shanghai Pujiang Program(No.21PJD030)。
文摘During solidifications of immiscible alloys,the motion of droplets at the solid/liquid(S/L)interface is gen-erally driven by dragging force,gravity force,repulsion force of interface,and thermal-solutal Marangoni force,However,there is few in situ study investigating kinetics behavior to analyze the forces on droplets.The mechanism of droplet motion remains unclear due to the unavailability or uncertainty of the effect of convection and solutal Marangoni force on droplet behavior.In this study,directional solidification of im-miscible Al-Bi alloy was observed via synchrotron radiography,and the horizontal oscillation of droplets at S/L interface was detected for the first time.Forces,especially solutal Marangoni force,were calcu-lated based on the in situ measured radius of droplets and thermal-solutal gradients.The experimental results cannot be reasonably explained by the previous analysis model which neglects melt convection.The non-negligible effect of flow on droplet motion was demonstrated,and the force balance of droplet both vertically and horizontally can be obtained considering a lift force of 6.39 × 10^(-9) N and a modified solute-related parameter dσ/dc of 0.45-0.65 J m^(-2),respectively.
基金financially supported by the National Natural Science Foundation of China(Nos.52173224,51821001,52130105,and 52273230)the Natural Science Foundation of Shanghai(No.21ZR1431200)the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning.
文摘Titanium diboride(TiB_(2))is an effective grain refiner of Al alloys in the industry that facilitates casting processes by forming uniformly refined microstructures.Although our understanding of the underlying refinement mechanisms has advanced,the atomic kinetics of heterogeneous nucleation of Al on TiB2 remains unknown.Here,we report atomic-scale observations of the heterogeneous nucleation and growth kinetics of Al on self-formed TiB_(2) particles by in situ heating of undercooled Al-5Ti-1B films.We demonstrate that an ordered Al monolayer forms on the Ti-terminated{0001}TiB_(2) surface;then,the surrounding Al atoms are initiated to form an island-shaped Al nucleus with face-centered cubic{111}stacking without the assistance of a Ti-rich buffer layer.The interfacial lattice mismatch between{111}Al and{0001}TiB_(2) causes remarkable out-of-plane strain that decreases gradually with Al nucleus layers increasing to 6 atomic layers.The elastic strain energy originating from this interfacial strain increases the free energy of the Al/TiB2 heterostructure,hence impeding the rapid growth of the Al nucleus.We found that TiB2 particles stabilize the Al nuclei rather than activating their free growth into grains when the experimental undercoolingΔT is lower than the onset undercoolingΔT fg in Greer's free growth model.Our findings provide an atomic-scale physical image of the heterogeneous nucleation and growth mechanisms of Al with inoculator participation and elucidate the strain-dependent growth kinetics of Al nuclei.
基金supported by the National Natural Science Foundation of China(Nos.51627802,51871152 and 51971237)the Shanghai Pujiang Program(No.21PJD030)the National Key Research and Development Program of China(No.2020YFB0311200)。
文摘Grain refinement of Al alloys inoculated by rare earth elements,such as Sc,has been extensively acknowledged,while the practical behavior of how inoculant Al_(3)Sc particles affect the refinement in solidification has not been clarified due to the non-transparency of the solidification process.Here,the microstructural evolution of primary Al_(3)Sc particles andα-Al grains in Al-10 wt.%Cu alloy solidifications with 0.2 wt.%,0.6 wt.%,and 1.0 wt.%Sc additions was investigated by in situ synchrotron X-ray radiography.The detailed mechanisms of curve motion of grains(CMG)and melt convection were revealed.The efficient grains nucleation,uniformly scattered small initial grains,and long duration of melt convection contributed to the best refinement in the 0.6 wt.%Sc addition sample.This work provides a deep insight into grain refinement in solidification with Sc addition,which will enlighten the composition design and casting process of Al alloys inoculated by rare earth elements.
基金financially supported by the National Science and Technology Major Project of China(Nos.J2019-VI-0004–0117 and 2017-VI0013–0085)the National Natural Science Foundation of China(Nos.52071205,52001205 and 51771118)。
文摘Ni Co Cr-based multi-component alloys have drawn much attention due to their exceptional ductility and strain hardening capacity.However,insufficient strength-ductility synergy of NiCoCr alloy has always been an issue that prevents it from extensive applications.According to our previous research,the precipitation ofγ”phase can significantly improve the strength-ductility synergy of this alloy system at room temperature.In this study,the effects of V addition onγ”phase stability and high-temperature mechanical properties have been explicitly investigated.The results indicate that V addition can stabilize the metastableγ”phase in this alloy system and prevent it from transforming into a stableδphase at grain boundaries upon 650℃aging,resulting in improved mechanical properties at elevated temperatures.The specific strength ofγ”-strengthened multi-component NiCoCr-based alloy can reach up to 86.2 MPa gcmat 650℃,which is higher than those of Ni-based superalloys,IN 939 and Waspaloy.This work provides theoretical guidance for the novel design of γ”-strengthened alloy for high-temperature applications.
基金financially supported by the National Natural Science Foundation of China (No.51874197)Natural Science Foundation of Shanghai (Nos.21ZR1429400,22ZR1429700)
文摘Rechargeable aluminum-sulfur(Al-S)batteries have been considered as a highly potential energy storage system owing to the high theoretical capacity,good safety,abundant natural reserves,and low cost of Al and S.However,the research progress of Al-S batteries is limited by the slow kinetics and shuttle effect of soluble polysulfides intermediates.Herein,an interconnected free-standing interlayer of iron sin-gle atoms supported on porous nitrogen-doped carbon nanofibers(FeSAs-NCF)on the separator is developed and used as both catalyst and chemical barrier for Al-S batteries.The atomically dispersed iron active sites(Fe-N_(4))are clearly identified by aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and X-ray absorption near-edge structure.The Al-S battery with the FeSAs-NCF shows an improved specific capacity of 780 mAh g^(−1)and enhanced cycle stability.As evidenced by experimental and theoretical results,the atomically dispersed iron active centers on the separator can chemically adsorb the polysulfides and accelerate reaction kinetics to inhibit the shuttle effect and promote the reversible conversion between aluminum polysulfides,thus improving the electrochemical performance of the Al-S battery.This work provides a new way that can not only promote the conversion of aluminum sulfides but also suppress the shuttle effect in Al-S batteries.
基金financially supported by the National Natural Science Foundation of China(Nos.U2037601,51775334 and 51821001)the National Key Research&Development Program of China(No.2016YFB0701205)+3 种基金the Joint Innovation Fund of CALT and College(No.CALT2020-TS07)the Open Fund of State Key Laboratory of Advanced Forming Technology and Equipment(No.SKL2020005)the Research Program of Joint Research Center of Advanced Spaceflight Technologies(No.USCAST2020-14)。
文摘The microstructure,aging behavior and mechanical properties of cast Mg–3Nd–3Gd–x Zn–0.5Zr(x=0,0.5,0.8,1 wt%)alloys are investigated in this work.Zn–Zr particles with different morphologies form during solution treatment due to the additions of Zn.As the Zn content increases,the number density of Zn–Zr particles also increases.Microstructural comparisons of peak-aged studied alloys indicate that varying Zn additions could profoundly influence the competitive precipitation behavior.In the peak-aged Zn-free alloy,β′′phases are the key strengthening precipitates.When 0.5 wt%Zn is added,besidesβ′′precipitates,additional fineβ_(1)precipitates form.With the addition of 0.8 wt%Zn,the peak-aged 0.8Zn alloy is characterized by predominantly prismaticβ_(1)and scanty basal precipitate distributions.The enhanced precipitation ofβ_(1)should be primarily attributable to the presence of increased Zn–Zr dispersoids.When Zn content further increases to 1 wt%,the precipitation of basal precipitates is markedly enhanced.Basal precipitates andβ_(1)phases are the key strengthening precipitates in the peak-aged 1Zn alloy.Tensile tests reveal that the relatively best tensile properties are achieved in the peak-aged alloy with 0.5 wt%Zn addition,whose yield strength,ultimate tensile strength and elongation are 179 MPa,301 MPa and 5.3%,respectively.
基金the financial supports from the National Natural Science Foundation of China (Grant No. 51771118, U1760110, and 51627802)the Science and Technology Committee of Shanghai Municipality (Grant No. 17QC1400800 and 16DZ2260602)the State Key Laboratory of Solidification Processing in NWPU (Grant No. SKLSP201732)
文摘For NiAI intermetallic compound with B2 structure, there is still no calculation combining models of sin- gle and multiple layers while using the same basic set. Furthermore, some recently proposed criteria for brittleness and toughness have not been used to analyze its deformation behavior. Thus, first-principles calculation was applied to comprehensively study the elastic properties, ideal strength, generalized stacking fault energy and surface energy of B2-NiA1 intermetallic compound. The results suggest that calculations based on the current basic set give more accurate lattice parameters and elastic moduli. The Pugh criterion and Cauchy pressure cannot be used to interpret the intrinsic brittleness of NiAI. In comparison, the ductility parameter based on the strain energy under elastic instability and ZCT and Rice criteria based on generalized stacking fault energy and surface energy successfully identify the intrinsic brittleness of the NiA1 intermetallic compound. The reason why [111] slip always occurs in the defor- mation along [100] direction was clarified by examining the critical value for brittle-ductile transition. The results of density of state indicate shear deformation has less impact on structural stability, and the change of charge density difference implies that 〈001〉 shear induces more intensive redistribution of charge density, which is well correlated to the brittleness and deformation behavior of NiAI intermetallic comnound.
