High(or medium)-entropy alloys(H/MEAs)are complex concentrated solid solutions prone to develop the chemical short-range orders(CSROs),as an indispensable structural constituent to make H/MEAs essentially different fr...High(or medium)-entropy alloys(H/MEAs)are complex concentrated solid solutions prone to develop the chemical short-range orders(CSROs),as an indispensable structural constituent to make H/MEAs essentially different from the traditional alloys.The CSROs are predicted to play roles in dislocation behaviors and mechanical properties.So far,the image of CSROs is built up by the theoretical modeling and computational simulations in terms of the conventional concept,i.e.,the preference/avoidance of elemental species to satisfy the short-ranged ordering in the first and the next couple of nearest-neighbor atomic shells.In these simulated CSROs,however,the structural image is missing on the atomic scale,even though the lattice periodicity does not exist in the CSROs.Further,it is pending as to the issues if and what kind of CSRO may be formed in a specific H/MEA.All these are ascribed to the challenge of experimentally seeing the CSROs.Until recently,the breakthrough does not appear to convincingly identify the CSROs in the H/MEAs by using the state-of-the-art transmission electron microscope.To be specific,the electron diffractions provide solid evidence to doubtlessly ascertain CSROs.The structure motif of CSROs is then constructed,showing both the lattice structure and species ordering occupation,along with the stereoscopic topography of the CSRO.It is suggested that the CSROs,as the first landscape along the path of development of the local chemical ordering,offer one more route to substantially develop the ordered structure on the atomic scale in the H/MEAs,parallel to the existing grain-leveled microstructure.The findings of CSROs make a step forward to understand the CSROs-oriented relationship between the microstructure and mechanical properties.This review focuses on the recent progress mainly in the experimental aspects of the identification,structure motif,and mechanical stability in CSROs,along with the chemical medium-range orders as the growing CSROs。展开更多
Layered transition metal oxides have emerged as promising cathode materials for sodium ion batteries.However,irreversible phase transitions cause structural distortion and cation rearrangement,leading to sluggish Na+d...Layered transition metal oxides have emerged as promising cathode materials for sodium ion batteries.However,irreversible phase transitions cause structural distortion and cation rearrangement,leading to sluggish Na+dynamics and rapid capacity decay.In this study,we propose a medium-entropy cathode by simultaneously introducing Fe,Mg,and Li dopants into a typical P2-type Na_(0.75)Ni_(0.25)Mn_(0.75)O_(2)cathode.The modified Na_(0.75)Ni_(0.2125)Mn_(0.6375)Fe_(0.05)Mg_(0.05)Li_(0.05)O_(2)cathode predominantly exhibits a main P2 phase(93.5%)with a minor O3 phase(6.5%).Through spectroscopy techniques and electrochemical investigations,we elucidate the redox mechanisms of Ni^(2+/3+/4+),Mn^(3+/4+),Fe^(3+/4+),and O_(2)-/O_(2)^(n-)during charging/discharging.The medium-entropy doping mitigates the detrimental P2-O_(2)phase transition at high-voltage,replacing it with a moderate and reversible structural evolution(P2-OP4),thereby enhancing structural stability.Consequently,the modified cathode exhibits a remarkable rate capacity of 108.4 mAh·g^(-1)at 10C,with a capacity retention of 99.0%after 200 cycles at 1C,82.5%after 500 cycles at 5C,and 76.7%after 600 cycles at 10C.Furthermore,it also demonstrates superior electrochemical performance at high cutoff voltage of 4.5 V and extreme temperature(55 and 0℃).This work offers solutions to critical challenges in sodium ion batteries cathode materials.展开更多
Facing the dual challenges of environmental pollution and energy crisis,photocatalytic water splitting for hydrogen(H_(2))production has emerged as a promising strategy to convert solar energy into storable chemical e...Facing the dual challenges of environmental pollution and energy crisis,photocatalytic water splitting for hydrogen(H_(2))production has emerged as a promising strategy to convert solar energy into storable chemical energy.In this work,the medium-entropy metal sulfides((FeCoNi)S_(2))as cocatalysts are successfully anchored onto protonated g-C_(3)N_(4)nanosheets(HCN NSs)to fabricated(FeCo-Ni)S_(2)-HCN composite via a solvothermal method.The photocatalytic hydrogen production rate of(FeCoNi)S_(2)-HCN composite reaches 2996μmol·h^(-1)·g^(-1),representing 83.22,9.16,and 1.34-fold enhancements compared to HCN(36μmol·h^(-1)·g^(-1)),FeS_(2)-HCN(327μmol·h^(-1)·g^(-1))and(FeCo)S_(2)-HCN(2240μmol·h^(-1)·g^(-1)).The apparent quantum efficiency of(FeCoNi)S_(2)-HCN composite attains 12.29% at λ=370 nm.Comprehensive characterizations and experimental analyses reveal that the superior photocatalytic performance stems from three synergistic mechanisms:(1)The curled-edge lamellar morphology of HCN nanosheets provides a large specific surface area,which enhances light absorption,facilitates electron transfer,and promotes cocatalyst loading.(2)(FeCoNi)S_(2)as cocatalyst expands the light absorption range and capacity,accelerates the separation and transfer of electron-hole pairs,and creates abundant active sites to trap photogenerated carriers for surface hydrogen evolution reactions.(3)The synergistic interactions among multiple metallic elements(Fe,Co and Ni)further enhance surface activity,increase photogenerated carrier density,and reduce charge transport resistance,ultimately optimizing hydrogen production efficiency.展开更多
With continuous enhancement of gas-turbine inlet temperature and rapid increase of radiant heat transfer,thermal barrier coating(TBC)materials with a combination of low thermal conductivity and good high-temperature t...With continuous enhancement of gas-turbine inlet temperature and rapid increase of radiant heat transfer,thermal barrier coating(TBC)materials with a combination of low thermal conductivity and good high-temperature thermal radiation shielding performance play vital roles in ensuring the durability of metallic blades.However,yttria-stabilized zirconia(YSZ),as the state-of-the-art TBC and current industry standard,is unable to meet such demands since it is almost translucent to high-temperature thermal radiation.Besides,poor corrosion resistance of YSZ to molten calcia-magnesia-alumina-silicates(CMAS)also impedes its application in sand,dust,or volcanic ash laden environments.In order to improve the hightemperature thermal radiation shielding performance and CMAS resistance of YSZ and further reduce its thermal conductivity,two medium-entropy(ME)oxide ceramics,ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),were designed and prepared by pressureless sintering of binary powder compacts in this work.ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)presents cubic structure but a trace amount of secondary phase,while ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)displays a combination of tetragonal phase(81.6 wt.%)and cubic phase(18.4 wt.%).Both ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)possess better high-temperature thermal radiation shielding performance than YSZ.Especially,the high-temperature thermal radiation shielding performance of ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)is superior to that of ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)due to its narrower band gap and correspondingly higher infrared absorbance(above 0.7)at the waveband of 1 to 5μm.The two ME oxides also display significantly lower thermal conductivity than YSZ and close thermal expansion coefficients(TECs)to YSZ and Ni-based superalloys.In addition,the two ME oxides possess excellent CMAS resistance.After attack by molten CMAS at 1250℃for 4 h,merely~2μm thick penetration layer has been formed and the structure below the penetration layer is still intact.These results demonstrate that ME(Me,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)(Me=Y and Ta),especially ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),are promising thermal barrier materials for high-temperature thermal radiation shielding and CMAS blocking.展开更多
A medium-entropy high-speed steel(ME-HSS)coating with the 76 at.%of Fe and multiple alloying elements was prepared by the wide-band laser cladding.Compared with the commercial W6 Mo5 Cr4 V2(M2)HSS coating which contai...A medium-entropy high-speed steel(ME-HSS)coating with the 76 at.%of Fe and multiple alloying elements was prepared by the wide-band laser cladding.Compared with the commercial W6 Mo5 Cr4 V2(M2)HSS coating which contains a large number of network lamellar M2 C-type carbides along the grain boundaries,the presented ME-HSS coating has a high quantity of fi ner and more uniformly dispersed M C-type carbides;on the other hand,the coating has less retained austenite and much lower brittleness as well as similar secondary hardening eff ect and tempering hardness.展开更多
The unique high-entropy and sluggish diffusion effects of amorphous high-entropy alloys endow them with excellent thermal stability and plastic deformation.In this work,the near-equiatomic TaTiZr amorphous medium-entr...The unique high-entropy and sluggish diffusion effects of amorphous high-entropy alloys endow them with excellent thermal stability and plastic deformation.In this work,the near-equiatomic TaTiZr amorphous medium-entropy alloy(AMEA)was prepared via the magnetron sputtering to investigate the microstructural thermostability and nanoindentation creep behavior.Thermal annealing below the glass transition temperature gave rise to the microstructural heterogeneity due to the positive mixing enthalpy in TaTiZr AMEA,which became increasingly enhanced with raising the annealing temperature.Correspondingly,there appeared a monotonic increase in hardness as well as the elastic/shear modulus,yet a reduction in strain-rate sensitivity m or an increment in shear transformation zone volume with annealing temperature.Meanwhile,the indentation morphology measured by atomic force microscope exhibited a significant transformation from pile-up to sink-in,demonstrating the degradation of plastic deformability with enhancing the microstructural heterogeneity.Based on the relaxation time spectra for Maxwell-Voigt model,the microstructural heterogeneity can restrain the activation of internal defects associated with the operation of flow units during creeping,further triggering the strain-strengthening behavior and improved creep resistance in the annealed samples.This work provides significant guidance for the structural design of high-performance amorphous alloys.展开更多
Refractory high/medium-entropy alloys(RH/MEAs)are known for their outstanding performance at el-evated temperatures;however,they usually exhibit poor room-temperature plasticity,which can be at-tributed to the non-uni...Refractory high/medium-entropy alloys(RH/MEAs)are known for their outstanding performance at el-evated temperatures;however,they usually exhibit poor room-temperature plasticity,which can be at-tributed to the non-uniform deformation that occurs at room temperature.Once cracks nucleate,they will rapidly propagate into vertical splitting cracks.Here,we introduce multiple phases including FCC and HCP phases into the NbMoTa RMEA via appropriate addition of carbon.The results show that multiple-phase synergy effectively suppresses non-uniform deformation,thereby delaying the onset of vertical splitting cracks.An optimal combination of compressive strength-plasticity is achieved by the(NbMoTa)_(92.5)C_(7.5) alloy.The significant improvement in room-temperature mechanical properties can be attributed to its hierarchical microstructure:in the mesoscale,the BCC matrix is divided by eutectic structures;while at the microscale,the BCC matrix is further refined by abundant lath-like FCC precipitates.The FCC precip-itates contain high-density stacking faults,acting as a dislocation source under compressive loading.The HCP phase in the eutectic microstructures,in turn,acts as a strong barrier to dislocation movement and simultaneously increases the dislocation storage capacity.These findings open a new route to tailor the microstructure and mechanical properties of RH/MEAs.展开更多
CoCrNi medium-entropy alloy has demonstrated remarkable mechanical properties,suggesting its potential as a structural material.Nevertheless,the challenge lies in achieving an elusive combination of high hardness and ...CoCrNi medium-entropy alloy has demonstrated remarkable mechanical properties,suggesting its potential as a structural material.Nevertheless,the challenge lies in achieving an elusive combination of high hardness and inherent self-lubrication on the worn surface,which is crucial for attaining exceptional tribological performance in medium-entropy alloy(MEA).This study reports the preparation of a novel CoCrNi-based self-lubricating composite by powder metallurgy,which is reinforced simultaneously with Ag solid lubricating phase and SiC ceramic particles.During the sintering process,SiC decomposes to form high hardness in situ Cr_(23)C_(6),enabling the composite to achieve high load-bearing capacity.During the sliding process,thick and dense Ag self-lubricating film is successfully achieved due to the mechanical and thermal effects.The protective tribo-layer effectively mitigates surface stress concentration induced by wear,thereby inhibiting surface coarsening and substantially enhancing the tribological performance.The results showed that compared with CoCrNi MEA,the wear rate and friction coefficient of CoCrNi/SiC/Ag composite are reduced by 88.1%and 32.8%,respectively,showing superior tribological properties over most MEA-based self-lubrication composites.This study further elucidates the wear mechanism of CoCrNi/SiC/Ag composite,providing a new strategy for developing self-lubricating materials with excellent comprehensive performance,which overcomes the inherent trade-off between wear resistance and lubrication.展开更多
Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications.The emerging face-centered cubic medium-entropy alloys(MEAs)demonstra...Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications.The emerging face-centered cubic medium-entropy alloys(MEAs)demonstrate outstanding mechanical properties at both ambient and cryogenic temperatures.They are anticipated to extend their applicability to elevated temperatures,owing to their inherent advantages in leveraging multiple strengthening and deformation mechanisms.Here,a dual heterostructure,comprising of heterogeneous grain structure with heterogeneous distribution of the micro-scale Nb-rich Laves phases,is introduced in a CrCoNi-based MEA through thermo-mechanical processing.Additionally,a high-density nano-coherentγ’phase is introduced within the grains through isothermal aging treatments.The superior thermal stability of the heterogeneously distributed precipitates enables the dual heterostructure to persist at temperatures up to 1073 K,allowing the MEA to maintain excellent mechanical properties across a wide temperature range.The yield strength of the dual-heterogeneous-structured MEA reaches up to 1.2 GPa,1.1 GPa,0.8 GPa,and 0.6 GPa,coupled with total elongation values of 28.6%,28.4%,12.6%,and 6.1%at 93 K,298 K,873 K,and 1073 K,respectively.The high yield strength primar-ily stems from precipitation strengthening and hetero-deformation-induced strengthening.The high flow stress and low stacking fault energy of the dual-heterogeneous-structured MEA promote the formation of high-density stacking faults and nanotwins during deformation from 93 K to 1073 K,and their density increase with decreasing deformation temperature.This greatly contributes to the enhanced strainhardening capability and ductility across a wide temperature range.This study offers a practical solution for designing dual-heterogeneous-structured MEAs with both high yield strength and large ductility across a wide temperature range.展开更多
The development of highly active, durable, and low-cost electrocatalysts is crucial for electrocatalytic hydrogen production. Ultrathin two-dimensional (2D) nanomaterials have extremely large specific surface areas, m...The development of highly active, durable, and low-cost electrocatalysts is crucial for electrocatalytic hydrogen production. Ultrathin two-dimensional (2D) nanomaterials have extremely large specific surface areas, making them highly desirable electrocatalyst morphologies. Medium-entropy alloys (MEAs) exhibit compositional tunability and entropy-driven structural stability, making them ideal electrocatalyst candidates. In this study, MoCoNi MEA with ultrathin 2D morphology was successfully developed using a facile ionic lay-er epitaxial method. The ultrathin 2D MoCoNi MEA showed an excellent oxygen evolution reaction (OER) electrocatalytic performance, with a low overpotential of 167 mV at a current density of 10 mA/cm^(2) and small Tafel slope of 33.2 mV/dec. At the overpotential of 167 mV, the ultrathin 2D MoCoNi MEA exhibited ultrahigh mass activity of 3359.6 A/g, which is three orders of magnitude higher than that of the commercial noble metal oxide RuO_(2) (1.15 A/g). This excellent electrocatalytic performance was attributed to the synergy of multiple active metal-induced medium entropies, as well as the ultrathin thickness, which considerably shortened the charge-transfer dis-tance and thus significantly promoted charge transfer. Owing to the natural entropy-stabilizing effect, the ultrathin 2D MoCoNi MEA maintained 90% of the initial current after a continuous OER electrocatalytic test for 134 h, showing impressive electrocatalytic stability. This study opens new avenues for the development of high-performance and low-cost electrocatalyst materials by creating MEAs with ultrathin 2D morphology.展开更多
Unraveling the essence of electronic structure effected by d-d orbital coupling of transition metal and methanol oxidation reaction(MOR)performance can fundamentally guide high efficient catalyst design.Herein,density...Unraveling the essence of electronic structure effected by d-d orbital coupling of transition metal and methanol oxidation reaction(MOR)performance can fundamentally guide high efficient catalyst design.Herein,density functional theory(DFT)calculations were performed at first to study the d–d orbital interaction of metallic Pt Pd Cu,revealing that the incorporation of Pd and Cu atoms into Pt system can enhance d-d electron interaction via capturing antibonding orbital electrons of Pt to fill the surrounding Pd and Cu atoms.Under the theoretical guidance,Pt Pd Cu medium entropy alloy aerogels(Pt Pd Cu MEAAs)catalysts have been designed and systematically screened for MOR under acid,alkaline and neutral electrolyte.Furthermore,DFT calculation and in-situ fourier transform infrared spectroscopy analysis indicate that Pt Pd Cu MEAAs follow the direct pathway via formate as the reactive intermediate to be directly oxidized to CO_(2).For practical direct methanol fuel cells(DMFCs),the Pt Pd Cu MEAAs-integrated ultra-thin catalyst layer(4–5μm thickness)as anode exhibits higher peak power density of 35 m W/cm^(2) than commercial Pt/C of 20 m W/cm^(2)(~40μm thickness)under the similar noble metal loading and an impressive stability retention at a 50-m A/cm^(2) constant current for 10 h.This work clearly proves that optimizing the intermediate adsorption capacity via d-d orbital coupling is an effective strategy to design highly efficient catalysts for DMFCs.展开更多
The equimolar NbZrTi medium-entropy alloy(MEA)has attracted attention due to its excellent comprehensive mechanical properties.In this study,the designed body-centered cubic NbZrTiAl_(4)(atomic percent,at%)MEA by Al a...The equimolar NbZrTi medium-entropy alloy(MEA)has attracted attention due to its excellent comprehensive mechanical properties.In this study,the designed body-centered cubic NbZrTiAl_(4)(atomic percent,at%)MEA by Al addition,having a superplastic extensibility of~5000%under cold rolling,enables directly fabricated ultrathin foils with a thickness down to~0.2 mm without any treatments.Particularly,the annealed NbZrTiAl_(4) MEA foils,containing a coherent nanoscale B2,exhibit an ultrahigh yield strength of up to~1130 MPa,which even surpasses the bulk counterpart,while maintaining a good fracture elongation of up to~14%.The Al addition induced a stronger solid solution strengthening and fine-grain strengthening in the foils.Complex dislocation interactions and dislocation–B2 interactions promoted a dynamical formation of dislocation bands,which yielded work-hardening ability and tensile ductility.These findings provide a novel strategy for the design of ultrathin refractory medium-entropy foils to break through their performance limits at ultrahigh temperatures and guide the design of high-performance lightweight foils for structural applications.展开更多
The strength-ductility trade-offwas evaded by deploying a triple-level heterogeneous structure into a CoNiV-based medium-entropy alloy(THS MEA).The innovative hetero-structures comprise chemical short-range ordering(C...The strength-ductility trade-offwas evaded by deploying a triple-level heterogeneous structure into a CoNiV-based medium-entropy alloy(THS MEA).The innovative hetero-structures comprise chemical short-range ordering(CSRO)at the atomic level,B2 precipitates at the nanoscale level,and heterogeneous grains at the microscale level.The THS MEA exhibits superior mechanical properties,displaying a yield strength from 1.1 GPa to 1.5 GPa alongside a uniform elongation of 18%-35%.Compared with its coarse-grained(CG)counterpart,the THS MEA demonstrates the pronounced up-turn phenomenon and enhanced hardening behavior attributed to hetero-deformation-induced(HDI)hardening.The detailed microstructural characterizations reveal that CG MEA primarily accommodates deformation through extensive planar dislocations and Taylor lattices.However,the THS MEA exhibits a more complex deformation profile,characterized by planar and waved dislocations,deformation twins,stacking faults,and Lomer-Cottrell locks.Additionally,the interactions between dislocations and B2 nanoprecipitates play a pivotal role in dislocation entanglements and accumulations.Furthermore,the CSRO within the matrix effectively retards the dislocation motion,contributing to a substantive hardening effect.These findings underscore the potential of a heterogeneous microstructure strategy in enhancing strain hardening for conquering the strength-ductility dilemma.展开更多
A heterogeneous CoNiCr_(2)eutectic medium-entropy alloy(EMEA),comprising soft face-centered cubic(FCC)and hard body-centered cubic(BCC)lamellae,associated with minor acicular hexagonal close-packed(HCP)phase precipita...A heterogeneous CoNiCr_(2)eutectic medium-entropy alloy(EMEA),comprising soft face-centered cubic(FCC)and hard body-centered cubic(BCC)lamellae,associated with minor acicular hexagonal close-packed(HCP)phase precipitated in BCC phase,was synthesized towards excellent tensile strength and ductility synergy.The tensile mechanical properties demonstrated that this alloy was temperature-dependent,i.e.,when the testing temperature reduced from room temperature(RT)to liquid nitrogen temperature(LNT),the yield strength,ultimate strength,and uniform elongation were enhanced from 449 MPa,821 MPa,and 5.0%to 702 MPa,1174 MPa,and 8.4%,respectively.The prominent elevation of yield strength at LNT mainly resulted from the dramatically enhanced lattice friction stress(σ0)and the FCC-BCC interfacial strengthening,while the improved ductility was attributed to the superior crack-arrest capability of FCC matrix stemmed from the accumulation of stacking faults(SFs)and enhancedσ0 at LNT.Additionally,although the deformation mechanisms were dominated by planar dislocation glides and SFs at both temperatures,the initiation of premature cracks in the BCC phase due to the inferior deformation capability at LNT constrained the better strength-ductility trade-off.The cracks in the BCC phase tended to propagate along the BCC-HCP interfaces because of the strain incompatibility.Further-more,the sub-nanoscale L1_(2) particles in the FCC matrix could not only strengthen this alloy but also im-prove the stacking fault energy leading to no deformation twinning even at LNT.This work may provide a guide for the design of remarkable strength and ductility synergy EMEAs combined with outstanding castability for applications at cryogenic temperatures.展开更多
Bacterial and mycoplasma infections pose a severe hazard to human life and property.These necessitate the development of antibacterial metallic materials that can be produced efficiently in large quantities.In this st...Bacterial and mycoplasma infections pose a severe hazard to human life and property.These necessitate the development of antibacterial metallic materials that can be produced efficiently in large quantities.In this study,an(Fe_(63.3)Mn_(14)Si_(9.1)Cr_(9.8)C_(3.8))_(86)Cu_(12)Ag_(2)medium-entropy alloy(MEA)consisting of in situ FCC1(austenite)and FCC2(Cu–Ag-rich)phases was prepared.It displayed a yield strength of 1100 MPa,fracture strength of 1921 MPa,and compressive plasticity of 27%at room temperature.This is attributed to the low stacking fault energy(3.7 m J m^(-2))inducing strong transformation-induced plasticity(TRIP),twinning-induced plasticity(TWIP),and lattice distortion.The alloy contained nano-and microscale antibacterial phases.This enabled it to achieve an antimicrobial efficiency higher than 99.9%against E.coli and S.aureus after6 h of exposure.The hot working efficiency makes it preferable for mass production with critical process parameters.A constitutive model was established using the Arrhenius equation to validate the applicability of the dynamic materials model(DMM).Subsequently,the hot processing map of the medium-entropy alloy was established based on the DMM.The optimal processing parameters were determined as 800℃with strain rates of10^(–1)–10^(–2)s^(-1).The low stacking fault energy ensures that dynamic recrystallization is the primary softening mechanism in the“safe”region.Finally,the density of states(DOS)of the MEA(determined by first-principles calculations)was significantly lower(162.1 eV)than those of Ni and Fe.This indicated a strong high-temperature stability.The DOS increased marginally with an increase in deformation.展开更多
Many machine components are operated in dry sliding,elevated temperature,and oxidizing environ-ments,leading to material failure or loss of functionality.Despite previous wear studies on conven-tional alloys,wear-rela...Many machine components are operated in dry sliding,elevated temperature,and oxidizing environ-ments,leading to material failure or loss of functionality.Despite previous wear studies on conven-tional alloys,wear-related properties in high-entropy alloys(HEAs)and medium-entropy alloys(MEAs)up to 1000℃ are rarely reported.Here we systematically study the high-temperature hardness,wear be-haviours and mechanisms of two popular MEAs,FeCoNi and CrCoNi,from room temperature to 1000℃.We find that the wear resistance of FeCoNi surpasses that of CrCoNi at room temperature,600℃,and 800℃.Contrarily,the wear resistance of CrCoNi surpasses that of FeCoNi at 400℃ and 1000℃.By characterizing wear tracks,we identify that these wear-mechanism transitions are associated with alloy elements,oxidation rates,and oxide types.At room temperature,FeCoNi forms a spinel oxide layer with a lower wear rate than CrCoNi.At 400℃,the wear rates of FeCoNi and CrCoNi are comparable because of temperature softening.At 600℃ and 800℃,FeCoNi shows Co_(3)O_(4) as the main constituent of the glaze layer,enhancing wear resistance compared to CrCoNi.At 1000℃,such glaze layer in FeCoNi undergoes severe plastic deformation,reducing its wear resistance;the Cr2 O3 oxide layer formed in CrCoNi remains hard and less deformable,contributing to its higher wear resistance.This study provides a fundamental understanding of the effect of principal elements on the wear performance in FeCoNi and CrCoNi-related MEAs and HEAs.展开更多
This study demonstrated the potential for customizing the desired properties of the Co_(18.5)Cr_(12)Fe_(55)Ni_(9)Mo_(3.5)C_(2)(at.%)ferrous medium-entropy alloy by manipulating the deformation-induced martensite trans...This study demonstrated the potential for customizing the desired properties of the Co_(18.5)Cr_(12)Fe_(55)Ni_(9)Mo_(3.5)C_(2)(at.%)ferrous medium-entropy alloy by manipulating the deformation-induced martensite transformation(DIMT)behavior at liquid nitrogen temperature.This was achieved by modifying various initial microstructures through annealing at temperatures ranging from 900 to 1200℃.The variations in DIMT kinetics were analyzed based on two main factors.(1)Inducing carbide precipitation by annealing at 900 and 1000°C results in changes in the composition within the matrix,which may affect the stability of the face-centered cubic phase.Samples with a higher volume fraction of the carbide precipitates exhibit lower-GFCC→BCC and faster DIMT kinetics.(2)The onset and kinetics of DIMT are also affected by the use of martensite nucleation sites,which may vary depending on the presence of non-recrystallized regions or the grain size.In fine-grained structures,martensite primarily nucleated in the non-recrystallized regions and grain boundaries.However,in coarse-grained microstructures,martensite mainly nucleated along the in-grain shear bands and their intersections.This precise control of the microstructure results in superior properties.The samples annealed at 900 and 1000°C with carbide precipitates and fine grains exhibit ultrahigh ultimate tensile strength,which may reach elevated values up to∼1.8 GPa,while those annealed at 1100 and 1200°C with larger grains and no precipitates exhibit a uniform elongation that exceeds 100%.展开更多
The development of medium-entropy alloys(MEAs)with superior mechanical properties and remarkable antibacterial performance has garnered significant attention in the field of metallic biomaterials.In this study,Ti-18Zr...The development of medium-entropy alloys(MEAs)with superior mechanical properties and remarkable antibacterial performance has garnered significant attention in the field of metallic biomaterials.In this study,Ti-18Zr-8Mo-10Cu MEAs with varying properties,including mechanical properties,corrosion resistance,antibacterial performance,and cytocompatibility,were obtained through heat treatment at 900℃for 1 h,followed by various cooling methods(water cooling,air cooling,and furnace cooling).An increasing cooling rate results in a decrease in the elastic modulus.The water-cooling specimen exhibits optimal ductility over 40%and minimum elastic modulus of 60 GPa.Moreover,the reduction in alloy composition segregation after heat treatment enhances the anticorrosion properties,exhibiting a robust passivation capability of MEAs.All synthesized Ti-18Zr-8Mo-10Cu ME As show favorable cytocompatibility and robust antibacterial rate approaching~100%at 12 and 24 h.Generally,the water-cooling specimen shows exceptional mechanical properties and outstanding antibacterial performance,holding considerable promise for future orthopedic applications.This study offers a viable approach to optimizing the comprehensive properties of copper-bearing Ti MEAs for biomedical applications.展开更多
Metal additive manufacturing(MAM)enables near-net shape production of components with minimized waste and excellent mechanical performance based on multi-scale microstructural heterogeneity.Espe-cially,the dislocation...Metal additive manufacturing(MAM)enables near-net shape production of components with minimized waste and excellent mechanical performance based on multi-scale microstructural heterogeneity.Espe-cially,the dislocation cell network that often bears elemental segregation or precipitation of a secondary phase contributes to enhancing the strength of additively manufactured materials.The cell boundaries can also act as active nucleation sites for the formation of precipitates under post-MAM heat treatment,as the chemical heterogeneity and profuse dislocations generate a driving force for precipitation.In this work,we subjected a Co_(18)Cr_(15)Fe_(50)Ni_(10)Mo_(6.5)C_(0.5)(at%)medium-entropy alloy fabricated by laser powder bed fusion(LPBF)to post-LPBF annealing at 900℃for 10 min.Microstructural investigation revealed that the cell boundaries of the as-built sample,which were decorated by Mo segregation,are replaced byμphase andM_(6)C typecarbide precipitatesduringannealingwhile thegrainstructureand sizeremain unaffected,indicating that the post-LPBF annealing delivered the proper amount of heat input to alter only the cell structure.The yield strength slightly decreased with annealing due to a reduction in the strengthening effect by the cell boundaries despite an increased precipitation strengthening effect.How-ever,the post-LPBF annealing improved the strain hardenability and the ultimate tensile strength was enhanced from∼1.02 to∼1.15 GPa owing to reinforced back stress hardening by the increased disloca-tion pile-up at the precipitates.Our results suggest that the cell structure with chemical heterogeneity can be successfully controlled by careful post-MAM heat treatment to tailor the mechanical performance,while also providing insight into alloy design for additive manufacturing.展开更多
High/medium entropy alloys(H/MEAs)have shown unique strengthening behavior and mechanical prop-erties because of the presence of massive local chemical orderings.Nevertheless,dynamic interactions between chemical shor...High/medium entropy alloys(H/MEAs)have shown unique strengthening behavior and mechanical prop-erties because of the presence of massive local chemical orderings.Nevertheless,dynamic interactions between chemical short-range orders(CSROs)and dislocations,and the underlying atomic strengthening mechanism remain elusive.In this work,we first developed a novel machine learning-embedded atom method(ML-EAM)potential of the CoNiV system,trained on a comprehensive first-principles dataset,which enables accurate and efficient modeling of CSRO formation and dislocation dynamics.Then,we in-vestigated the strengthening mechanisms of CSROs in CoNiV MEA through machine learning-augmented molecular dynamics(MD)simulations.Hybrid MD/Monte Carlo simulations reveal that CSRO domains possess an L1_(2)(NiCo)_(3) V structure,whose size increases with lowering annealing temperatures.These domains significantly enhance strength by impeding dislocation motion through complex energy path-ways,increasing depinning forces,and reducing mobility.Moreover,the MD simulations combined with theoretical analysis elucidate the competition between CSRO-assisted strengthening(via antiphase bound-ary formation)and solid solution weakening(via reduced atomic misfit volume).Phonon-drag effects are also amplified by CSROs,further resisting dislocation glide.Our results demonstrate that L1_(2)-CSROs strengthen CoNiV MEA primarily through antiphase boundary and phonon-drag contributions,providing new insights for designing high-performance multi-principal-element alloys via tailoring CSROs.展开更多
基金supported by the National Key Research and Development Program of the Ministry of Science and Technology of China(No.2019YFA0209902)the National Natural Science Foundation of China(Nos.11998102,11972350,and 11790293)the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB22040503).
文摘High(or medium)-entropy alloys(H/MEAs)are complex concentrated solid solutions prone to develop the chemical short-range orders(CSROs),as an indispensable structural constituent to make H/MEAs essentially different from the traditional alloys.The CSROs are predicted to play roles in dislocation behaviors and mechanical properties.So far,the image of CSROs is built up by the theoretical modeling and computational simulations in terms of the conventional concept,i.e.,the preference/avoidance of elemental species to satisfy the short-ranged ordering in the first and the next couple of nearest-neighbor atomic shells.In these simulated CSROs,however,the structural image is missing on the atomic scale,even though the lattice periodicity does not exist in the CSROs.Further,it is pending as to the issues if and what kind of CSRO may be formed in a specific H/MEA.All these are ascribed to the challenge of experimentally seeing the CSROs.Until recently,the breakthrough does not appear to convincingly identify the CSROs in the H/MEAs by using the state-of-the-art transmission electron microscope.To be specific,the electron diffractions provide solid evidence to doubtlessly ascertain CSROs.The structure motif of CSROs is then constructed,showing both the lattice structure and species ordering occupation,along with the stereoscopic topography of the CSRO.It is suggested that the CSROs,as the first landscape along the path of development of the local chemical ordering,offer one more route to substantially develop the ordered structure on the atomic scale in the H/MEAs,parallel to the existing grain-leveled microstructure.The findings of CSROs make a step forward to understand the CSROs-oriented relationship between the microstructure and mechanical properties.This review focuses on the recent progress mainly in the experimental aspects of the identification,structure motif,and mechanical stability in CSROs,along with the chemical medium-range orders as the growing CSROs。
基金supported by the National Natural Science Foundation of China(No.21805018)by Sichuan Science and Technology Program(Nos.2022ZHCG0018,2023NSFSC0117 and 2023ZHCG0060)Yibin Science and Technology Program(No.2022JB005)and China Postdoctoral Science Foundation(No.2022M722704).
文摘Layered transition metal oxides have emerged as promising cathode materials for sodium ion batteries.However,irreversible phase transitions cause structural distortion and cation rearrangement,leading to sluggish Na+dynamics and rapid capacity decay.In this study,we propose a medium-entropy cathode by simultaneously introducing Fe,Mg,and Li dopants into a typical P2-type Na_(0.75)Ni_(0.25)Mn_(0.75)O_(2)cathode.The modified Na_(0.75)Ni_(0.2125)Mn_(0.6375)Fe_(0.05)Mg_(0.05)Li_(0.05)O_(2)cathode predominantly exhibits a main P2 phase(93.5%)with a minor O3 phase(6.5%).Through spectroscopy techniques and electrochemical investigations,we elucidate the redox mechanisms of Ni^(2+/3+/4+),Mn^(3+/4+),Fe^(3+/4+),and O_(2)-/O_(2)^(n-)during charging/discharging.The medium-entropy doping mitigates the detrimental P2-O_(2)phase transition at high-voltage,replacing it with a moderate and reversible structural evolution(P2-OP4),thereby enhancing structural stability.Consequently,the modified cathode exhibits a remarkable rate capacity of 108.4 mAh·g^(-1)at 10C,with a capacity retention of 99.0%after 200 cycles at 1C,82.5%after 500 cycles at 5C,and 76.7%after 600 cycles at 10C.Furthermore,it also demonstrates superior electrochemical performance at high cutoff voltage of 4.5 V and extreme temperature(55 and 0℃).This work offers solutions to critical challenges in sodium ion batteries cathode materials.
文摘Facing the dual challenges of environmental pollution and energy crisis,photocatalytic water splitting for hydrogen(H_(2))production has emerged as a promising strategy to convert solar energy into storable chemical energy.In this work,the medium-entropy metal sulfides((FeCoNi)S_(2))as cocatalysts are successfully anchored onto protonated g-C_(3)N_(4)nanosheets(HCN NSs)to fabricated(FeCo-Ni)S_(2)-HCN composite via a solvothermal method.The photocatalytic hydrogen production rate of(FeCoNi)S_(2)-HCN composite reaches 2996μmol·h^(-1)·g^(-1),representing 83.22,9.16,and 1.34-fold enhancements compared to HCN(36μmol·h^(-1)·g^(-1)),FeS_(2)-HCN(327μmol·h^(-1)·g^(-1))and(FeCo)S_(2)-HCN(2240μmol·h^(-1)·g^(-1)).The apparent quantum efficiency of(FeCoNi)S_(2)-HCN composite attains 12.29% at λ=370 nm.Comprehensive characterizations and experimental analyses reveal that the superior photocatalytic performance stems from three synergistic mechanisms:(1)The curled-edge lamellar morphology of HCN nanosheets provides a large specific surface area,which enhances light absorption,facilitates electron transfer,and promotes cocatalyst loading.(2)(FeCoNi)S_(2)as cocatalyst expands the light absorption range and capacity,accelerates the separation and transfer of electron-hole pairs,and creates abundant active sites to trap photogenerated carriers for surface hydrogen evolution reactions.(3)The synergistic interactions among multiple metallic elements(Fe,Co and Ni)further enhance surface activity,increase photogenerated carrier density,and reduce charge transport resistance,ultimately optimizing hydrogen production efficiency.
基金financially supported by the National Natural Science Foundation of China(No.51772275 and No.51972089)Distinguished Young Foundation of Henan Province(No.202300410355)。
文摘With continuous enhancement of gas-turbine inlet temperature and rapid increase of radiant heat transfer,thermal barrier coating(TBC)materials with a combination of low thermal conductivity and good high-temperature thermal radiation shielding performance play vital roles in ensuring the durability of metallic blades.However,yttria-stabilized zirconia(YSZ),as the state-of-the-art TBC and current industry standard,is unable to meet such demands since it is almost translucent to high-temperature thermal radiation.Besides,poor corrosion resistance of YSZ to molten calcia-magnesia-alumina-silicates(CMAS)also impedes its application in sand,dust,or volcanic ash laden environments.In order to improve the hightemperature thermal radiation shielding performance and CMAS resistance of YSZ and further reduce its thermal conductivity,two medium-entropy(ME)oxide ceramics,ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),were designed and prepared by pressureless sintering of binary powder compacts in this work.ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)presents cubic structure but a trace amount of secondary phase,while ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)displays a combination of tetragonal phase(81.6 wt.%)and cubic phase(18.4 wt.%).Both ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)and ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)possess better high-temperature thermal radiation shielding performance than YSZ.Especially,the high-temperature thermal radiation shielding performance of ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)is superior to that of ME(Y,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)due to its narrower band gap and correspondingly higher infrared absorbance(above 0.7)at the waveband of 1 to 5μm.The two ME oxides also display significantly lower thermal conductivity than YSZ and close thermal expansion coefficients(TECs)to YSZ and Ni-based superalloys.In addition,the two ME oxides possess excellent CMAS resistance.After attack by molten CMAS at 1250℃for 4 h,merely~2μm thick penetration layer has been formed and the structure below the penetration layer is still intact.These results demonstrate that ME(Me,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2)(Me=Y and Ta),especially ME(Ta,Ti)_(0.1)(Zr,Hf,Ce)_(0.9)O_(2),are promising thermal barrier materials for high-temperature thermal radiation shielding and CMAS blocking.
基金financially supported by the National Natural Science Foundation of China(Nos.51971001,U1560105 and 51601050)Open Fund from State Key Laboratory of Solid Lubricating(No.LSL-1714)。
文摘A medium-entropy high-speed steel(ME-HSS)coating with the 76 at.%of Fe and multiple alloying elements was prepared by the wide-band laser cladding.Compared with the commercial W6 Mo5 Cr4 V2(M2)HSS coating which contains a large number of network lamellar M2 C-type carbides along the grain boundaries,the presented ME-HSS coating has a high quantity of fi ner and more uniformly dispersed M C-type carbides;on the other hand,the coating has less retained austenite and much lower brittleness as well as similar secondary hardening eff ect and tempering hardness.
基金financially supported by the National Natural Science Foundation of China(Nos.U2067219,52371118,92163201,U23A6013,92360301,and U2330203)Shaanxi Province Innovation Team Project(No.2024RS-CXTD-58)the Fundamental Research Funds for the Central Universities(Nos.xtr042024014 and xtr062024006).
文摘The unique high-entropy and sluggish diffusion effects of amorphous high-entropy alloys endow them with excellent thermal stability and plastic deformation.In this work,the near-equiatomic TaTiZr amorphous medium-entropy alloy(AMEA)was prepared via the magnetron sputtering to investigate the microstructural thermostability and nanoindentation creep behavior.Thermal annealing below the glass transition temperature gave rise to the microstructural heterogeneity due to the positive mixing enthalpy in TaTiZr AMEA,which became increasingly enhanced with raising the annealing temperature.Correspondingly,there appeared a monotonic increase in hardness as well as the elastic/shear modulus,yet a reduction in strain-rate sensitivity m or an increment in shear transformation zone volume with annealing temperature.Meanwhile,the indentation morphology measured by atomic force microscope exhibited a significant transformation from pile-up to sink-in,demonstrating the degradation of plastic deformability with enhancing the microstructural heterogeneity.Based on the relaxation time spectra for Maxwell-Voigt model,the microstructural heterogeneity can restrain the activation of internal defects associated with the operation of flow units during creeping,further triggering the strain-strengthening behavior and improved creep resistance in the annealed samples.This work provides significant guidance for the structural design of high-performance amorphous alloys.
基金financial support from the Na-tional Natural Science Foundation of China(No.52231006)National Key Research and Development Program of China(No.2017YFB0702003)the National Natural Science Foundation of China(No.51871217).
文摘Refractory high/medium-entropy alloys(RH/MEAs)are known for their outstanding performance at el-evated temperatures;however,they usually exhibit poor room-temperature plasticity,which can be at-tributed to the non-uniform deformation that occurs at room temperature.Once cracks nucleate,they will rapidly propagate into vertical splitting cracks.Here,we introduce multiple phases including FCC and HCP phases into the NbMoTa RMEA via appropriate addition of carbon.The results show that multiple-phase synergy effectively suppresses non-uniform deformation,thereby delaying the onset of vertical splitting cracks.An optimal combination of compressive strength-plasticity is achieved by the(NbMoTa)_(92.5)C_(7.5) alloy.The significant improvement in room-temperature mechanical properties can be attributed to its hierarchical microstructure:in the mesoscale,the BCC matrix is divided by eutectic structures;while at the microscale,the BCC matrix is further refined by abundant lath-like FCC precipitates.The FCC precip-itates contain high-density stacking faults,acting as a dislocation source under compressive loading.The HCP phase in the eutectic microstructures,in turn,acts as a strong barrier to dislocation movement and simultaneously increases the dislocation storage capacity.These findings open a new route to tailor the microstructure and mechanical properties of RH/MEAs.
基金supported by the Natural Science Foundation of China(Nos.52175188 and 52274367)the Key Research and Development Program of Shaanxi Province(No.2023-YBGY-434)+2 种基金he Open Fund of Liaoning Provincial Key Laboratory of Aero-engine Materials Tribology(No.LKLAMTF202301)Guangdong Basic and Applied Basic Research Foundation(No.2024A1515012378)the Science and Technology on Reactor System Design Technology Laboratory.
文摘CoCrNi medium-entropy alloy has demonstrated remarkable mechanical properties,suggesting its potential as a structural material.Nevertheless,the challenge lies in achieving an elusive combination of high hardness and inherent self-lubrication on the worn surface,which is crucial for attaining exceptional tribological performance in medium-entropy alloy(MEA).This study reports the preparation of a novel CoCrNi-based self-lubricating composite by powder metallurgy,which is reinforced simultaneously with Ag solid lubricating phase and SiC ceramic particles.During the sintering process,SiC decomposes to form high hardness in situ Cr_(23)C_(6),enabling the composite to achieve high load-bearing capacity.During the sliding process,thick and dense Ag self-lubricating film is successfully achieved due to the mechanical and thermal effects.The protective tribo-layer effectively mitigates surface stress concentration induced by wear,thereby inhibiting surface coarsening and substantially enhancing the tribological performance.The results showed that compared with CoCrNi MEA,the wear rate and friction coefficient of CoCrNi/SiC/Ag composite are reduced by 88.1%and 32.8%,respectively,showing superior tribological properties over most MEA-based self-lubrication composites.This study further elucidates the wear mechanism of CoCrNi/SiC/Ag composite,providing a new strategy for developing self-lubricating materials with excellent comprehensive performance,which overcomes the inherent trade-off between wear resistance and lubrication.
基金supported by the Tianjin Science and Technology Plan Project(No.22JCQNJC01280)the Central Funds Guiding the Local Science and Technology Development of Hebei Province(Nos.226Z1001G and 226Z1012G)+1 种基金the National Natural Science Foundation of China(No.52002109,52071124)the Young Elite Scientists Sponsorship Program by CAST(No.2022QNRC001).
文摘Developing alloys with exceptional strength-ductility combinations across a broad temperature range is crucial for advanced structural applications.The emerging face-centered cubic medium-entropy alloys(MEAs)demonstrate outstanding mechanical properties at both ambient and cryogenic temperatures.They are anticipated to extend their applicability to elevated temperatures,owing to their inherent advantages in leveraging multiple strengthening and deformation mechanisms.Here,a dual heterostructure,comprising of heterogeneous grain structure with heterogeneous distribution of the micro-scale Nb-rich Laves phases,is introduced in a CrCoNi-based MEA through thermo-mechanical processing.Additionally,a high-density nano-coherentγ’phase is introduced within the grains through isothermal aging treatments.The superior thermal stability of the heterogeneously distributed precipitates enables the dual heterostructure to persist at temperatures up to 1073 K,allowing the MEA to maintain excellent mechanical properties across a wide temperature range.The yield strength of the dual-heterogeneous-structured MEA reaches up to 1.2 GPa,1.1 GPa,0.8 GPa,and 0.6 GPa,coupled with total elongation values of 28.6%,28.4%,12.6%,and 6.1%at 93 K,298 K,873 K,and 1073 K,respectively.The high yield strength primar-ily stems from precipitation strengthening and hetero-deformation-induced strengthening.The high flow stress and low stacking fault energy of the dual-heterogeneous-structured MEA promote the formation of high-density stacking faults and nanotwins during deformation from 93 K to 1073 K,and their density increase with decreasing deformation temperature.This greatly contributes to the enhanced strainhardening capability and ductility across a wide temperature range.This study offers a practical solution for designing dual-heterogeneous-structured MEAs with both high yield strength and large ductility across a wide temperature range.
基金supported by the Fundamental Research Funds for the Central Universities(No.2024JBZY008)National Natural Science Foundation of China(No.52401031)+1 种基金the Talent Fund of Beijing Jiaotong University,China(No.2024XKRC064)the National College Students Innovative Entrepreneurial Training Program(No.202510004157).
文摘The development of highly active, durable, and low-cost electrocatalysts is crucial for electrocatalytic hydrogen production. Ultrathin two-dimensional (2D) nanomaterials have extremely large specific surface areas, making them highly desirable electrocatalyst morphologies. Medium-entropy alloys (MEAs) exhibit compositional tunability and entropy-driven structural stability, making them ideal electrocatalyst candidates. In this study, MoCoNi MEA with ultrathin 2D morphology was successfully developed using a facile ionic lay-er epitaxial method. The ultrathin 2D MoCoNi MEA showed an excellent oxygen evolution reaction (OER) electrocatalytic performance, with a low overpotential of 167 mV at a current density of 10 mA/cm^(2) and small Tafel slope of 33.2 mV/dec. At the overpotential of 167 mV, the ultrathin 2D MoCoNi MEA exhibited ultrahigh mass activity of 3359.6 A/g, which is three orders of magnitude higher than that of the commercial noble metal oxide RuO_(2) (1.15 A/g). This excellent electrocatalytic performance was attributed to the synergy of multiple active metal-induced medium entropies, as well as the ultrathin thickness, which considerably shortened the charge-transfer dis-tance and thus significantly promoted charge transfer. Owing to the natural entropy-stabilizing effect, the ultrathin 2D MoCoNi MEA maintained 90% of the initial current after a continuous OER electrocatalytic test for 134 h, showing impressive electrocatalytic stability. This study opens new avenues for the development of high-performance and low-cost electrocatalyst materials by creating MEAs with ultrathin 2D morphology.
基金financially supported by the National Natural Science Foundation of China(Nos.52073214 and 22075211)Guangxi Natural Science Fund for Distinguished Young Scholars(No.2024GXNSFFA010008)+5 种基金Natural Science Foundation of Shandong Province(Nos.ZR2023MB049 and ZR2021QB129)China Postdoctoral Science Foundation(No.2020M670483)Science Foundation of Weifang University(No.2023BS11)supported by the open research fund of the Laboratory of Xinjiang Native Medicinal and Edible Plant Resources Chemistry at Kashi Universitysupported by the Tianhe Qingsuo Open Research Fund of TSYS in 2022 and NSCC-TJNankai University Large-scale Instrument Experimental Technology R&D Project(No.21NKSYJS09)。
文摘Unraveling the essence of electronic structure effected by d-d orbital coupling of transition metal and methanol oxidation reaction(MOR)performance can fundamentally guide high efficient catalyst design.Herein,density functional theory(DFT)calculations were performed at first to study the d–d orbital interaction of metallic Pt Pd Cu,revealing that the incorporation of Pd and Cu atoms into Pt system can enhance d-d electron interaction via capturing antibonding orbital electrons of Pt to fill the surrounding Pd and Cu atoms.Under the theoretical guidance,Pt Pd Cu medium entropy alloy aerogels(Pt Pd Cu MEAAs)catalysts have been designed and systematically screened for MOR under acid,alkaline and neutral electrolyte.Furthermore,DFT calculation and in-situ fourier transform infrared spectroscopy analysis indicate that Pt Pd Cu MEAAs follow the direct pathway via formate as the reactive intermediate to be directly oxidized to CO_(2).For practical direct methanol fuel cells(DMFCs),the Pt Pd Cu MEAAs-integrated ultra-thin catalyst layer(4–5μm thickness)as anode exhibits higher peak power density of 35 m W/cm^(2) than commercial Pt/C of 20 m W/cm^(2)(~40μm thickness)under the similar noble metal loading and an impressive stability retention at a 50-m A/cm^(2) constant current for 10 h.This work clearly proves that optimizing the intermediate adsorption capacity via d-d orbital coupling is an effective strategy to design highly efficient catalysts for DMFCs.
基金funded by the Youth Fund Project of GRINM(No.66922309)the National Natural Science Foundation of China(No.52301220)。
文摘The equimolar NbZrTi medium-entropy alloy(MEA)has attracted attention due to its excellent comprehensive mechanical properties.In this study,the designed body-centered cubic NbZrTiAl_(4)(atomic percent,at%)MEA by Al addition,having a superplastic extensibility of~5000%under cold rolling,enables directly fabricated ultrathin foils with a thickness down to~0.2 mm without any treatments.Particularly,the annealed NbZrTiAl_(4) MEA foils,containing a coherent nanoscale B2,exhibit an ultrahigh yield strength of up to~1130 MPa,which even surpasses the bulk counterpart,while maintaining a good fracture elongation of up to~14%.The Al addition induced a stronger solid solution strengthening and fine-grain strengthening in the foils.Complex dislocation interactions and dislocation–B2 interactions promoted a dynamical formation of dislocation bands,which yielded work-hardening ability and tensile ductility.These findings provide a novel strategy for the design of ultrathin refractory medium-entropy foils to break through their performance limits at ultrahigh temperatures and guide the design of high-performance lightweight foils for structural applications.
基金financially supported by the NSFC Basic Science Center Program for“Multiscale Problems in Nonlinear Mechanics”(No.11988102)the National Key R&D Program of China(No.2019YFA0209902)+2 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB0510301)the National Natural Science Foundation of China(Nos.52192591 and 52071326)the Hong Kong Research Grants Council(No.GRF 11214121)。
文摘The strength-ductility trade-offwas evaded by deploying a triple-level heterogeneous structure into a CoNiV-based medium-entropy alloy(THS MEA).The innovative hetero-structures comprise chemical short-range ordering(CSRO)at the atomic level,B2 precipitates at the nanoscale level,and heterogeneous grains at the microscale level.The THS MEA exhibits superior mechanical properties,displaying a yield strength from 1.1 GPa to 1.5 GPa alongside a uniform elongation of 18%-35%.Compared with its coarse-grained(CG)counterpart,the THS MEA demonstrates the pronounced up-turn phenomenon and enhanced hardening behavior attributed to hetero-deformation-induced(HDI)hardening.The detailed microstructural characterizations reveal that CG MEA primarily accommodates deformation through extensive planar dislocations and Taylor lattices.However,the THS MEA exhibits a more complex deformation profile,characterized by planar and waved dislocations,deformation twins,stacking faults,and Lomer-Cottrell locks.Additionally,the interactions between dislocations and B2 nanoprecipitates play a pivotal role in dislocation entanglements and accumulations.Furthermore,the CSRO within the matrix effectively retards the dislocation motion,contributing to a substantive hardening effect.These findings underscore the potential of a heterogeneous microstructure strategy in enhancing strain hardening for conquering the strength-ductility dilemma.
基金the National Natural Science Foundation of China(Grant Nos.51931005,52171048)the Key Research and Development Program of Shaanxi Province(No.2020ZDLGY12-02).
文摘A heterogeneous CoNiCr_(2)eutectic medium-entropy alloy(EMEA),comprising soft face-centered cubic(FCC)and hard body-centered cubic(BCC)lamellae,associated with minor acicular hexagonal close-packed(HCP)phase precipitated in BCC phase,was synthesized towards excellent tensile strength and ductility synergy.The tensile mechanical properties demonstrated that this alloy was temperature-dependent,i.e.,when the testing temperature reduced from room temperature(RT)to liquid nitrogen temperature(LNT),the yield strength,ultimate strength,and uniform elongation were enhanced from 449 MPa,821 MPa,and 5.0%to 702 MPa,1174 MPa,and 8.4%,respectively.The prominent elevation of yield strength at LNT mainly resulted from the dramatically enhanced lattice friction stress(σ0)and the FCC-BCC interfacial strengthening,while the improved ductility was attributed to the superior crack-arrest capability of FCC matrix stemmed from the accumulation of stacking faults(SFs)and enhancedσ0 at LNT.Additionally,although the deformation mechanisms were dominated by planar dislocation glides and SFs at both temperatures,the initiation of premature cracks in the BCC phase due to the inferior deformation capability at LNT constrained the better strength-ductility trade-off.The cracks in the BCC phase tended to propagate along the BCC-HCP interfaces because of the strain incompatibility.Further-more,the sub-nanoscale L1_(2) particles in the FCC matrix could not only strengthen this alloy but also im-prove the stacking fault energy leading to no deformation twinning even at LNT.This work may provide a guide for the design of remarkable strength and ductility synergy EMEAs combined with outstanding castability for applications at cryogenic temperatures.
基金financially supported by the Science and Technology Program Project of Gansu Province(No.24ZD13GA018)the National Natural Science Foundation of China(Nos.12404230 and 52061027)+1 种基金Zhejiang Provincial Natural Science Foundation of China(No.LY23E010002)Lanzhou Youth Science and Technology Talent Innovation Project(No.2023-QN-91)
文摘Bacterial and mycoplasma infections pose a severe hazard to human life and property.These necessitate the development of antibacterial metallic materials that can be produced efficiently in large quantities.In this study,an(Fe_(63.3)Mn_(14)Si_(9.1)Cr_(9.8)C_(3.8))_(86)Cu_(12)Ag_(2)medium-entropy alloy(MEA)consisting of in situ FCC1(austenite)and FCC2(Cu–Ag-rich)phases was prepared.It displayed a yield strength of 1100 MPa,fracture strength of 1921 MPa,and compressive plasticity of 27%at room temperature.This is attributed to the low stacking fault energy(3.7 m J m^(-2))inducing strong transformation-induced plasticity(TRIP),twinning-induced plasticity(TWIP),and lattice distortion.The alloy contained nano-and microscale antibacterial phases.This enabled it to achieve an antimicrobial efficiency higher than 99.9%against E.coli and S.aureus after6 h of exposure.The hot working efficiency makes it preferable for mass production with critical process parameters.A constitutive model was established using the Arrhenius equation to validate the applicability of the dynamic materials model(DMM).Subsequently,the hot processing map of the medium-entropy alloy was established based on the DMM.The optimal processing parameters were determined as 800℃with strain rates of10^(–1)–10^(–2)s^(-1).The low stacking fault energy ensures that dynamic recrystallization is the primary softening mechanism in the“safe”region.Finally,the density of states(DOS)of the MEA(determined by first-principles calculations)was significantly lower(162.1 eV)than those of Ni and Fe.This indicated a strong high-temperature stability.The DOS increased marginally with an increase in deformation.
基金financial support from the Natural Sciences and Engineering Research Council of Canada(NSERC Discovery Grant#RGPIN-2018-05731 and NSERC Alliance Grant-Missions ALLRP 570708-2021)Dean’s Spark As-sistant Professorship in the Faculty of Applied Science&Engi-neering at the University of Toronto+7 种基金supported by the Canada Foundation for Innovation(CFI)the Natural Sciences and Engineer-ing Research Council(NSERC)the National Research Council(NRC)the Canadian Institutes of Health Research(CIHR)the Government of Saskatchewanthe University of SaskatchewanSeed fund from the Low-Carbon Renewable Material Center at the University of Torontofinancial support from the China Scholarship Council(CSC:No.202006230136).
文摘Many machine components are operated in dry sliding,elevated temperature,and oxidizing environ-ments,leading to material failure or loss of functionality.Despite previous wear studies on conven-tional alloys,wear-related properties in high-entropy alloys(HEAs)and medium-entropy alloys(MEAs)up to 1000℃ are rarely reported.Here we systematically study the high-temperature hardness,wear be-haviours and mechanisms of two popular MEAs,FeCoNi and CrCoNi,from room temperature to 1000℃.We find that the wear resistance of FeCoNi surpasses that of CrCoNi at room temperature,600℃,and 800℃.Contrarily,the wear resistance of CrCoNi surpasses that of FeCoNi at 400℃ and 1000℃.By characterizing wear tracks,we identify that these wear-mechanism transitions are associated with alloy elements,oxidation rates,and oxide types.At room temperature,FeCoNi forms a spinel oxide layer with a lower wear rate than CrCoNi.At 400℃,the wear rates of FeCoNi and CrCoNi are comparable because of temperature softening.At 600℃ and 800℃,FeCoNi shows Co_(3)O_(4) as the main constituent of the glaze layer,enhancing wear resistance compared to CrCoNi.At 1000℃,such glaze layer in FeCoNi undergoes severe plastic deformation,reducing its wear resistance;the Cr2 O3 oxide layer formed in CrCoNi remains hard and less deformable,contributing to its higher wear resistance.This study provides a fundamental understanding of the effect of principal elements on the wear performance in FeCoNi and CrCoNi-related MEAs and HEAs.
基金supported by the Nano&Material Technology Development Program through the National Research Foundation of Korea(NRF)funded by the Ministry of Science and ICT(No.RS-2023-00281246).
文摘This study demonstrated the potential for customizing the desired properties of the Co_(18.5)Cr_(12)Fe_(55)Ni_(9)Mo_(3.5)C_(2)(at.%)ferrous medium-entropy alloy by manipulating the deformation-induced martensite transformation(DIMT)behavior at liquid nitrogen temperature.This was achieved by modifying various initial microstructures through annealing at temperatures ranging from 900 to 1200℃.The variations in DIMT kinetics were analyzed based on two main factors.(1)Inducing carbide precipitation by annealing at 900 and 1000°C results in changes in the composition within the matrix,which may affect the stability of the face-centered cubic phase.Samples with a higher volume fraction of the carbide precipitates exhibit lower-GFCC→BCC and faster DIMT kinetics.(2)The onset and kinetics of DIMT are also affected by the use of martensite nucleation sites,which may vary depending on the presence of non-recrystallized regions or the grain size.In fine-grained structures,martensite primarily nucleated in the non-recrystallized regions and grain boundaries.However,in coarse-grained microstructures,martensite mainly nucleated along the in-grain shear bands and their intersections.This precise control of the microstructure results in superior properties.The samples annealed at 900 and 1000°C with carbide precipitates and fine grains exhibit ultrahigh ultimate tensile strength,which may reach elevated values up to∼1.8 GPa,while those annealed at 1100 and 1200°C with larger grains and no precipitates exhibit a uniform elongation that exceeds 100%.
基金financially supported by the National Natural Science Foundation of China(Nos.52231005 and 52001324)the Start-up Research Fund of Southeast University(No.RF1028623113)+1 种基金the Laboratory of Advanced Metallic Materials,Southeast University(Nos.AMM2025A01,AMM2024A02,and AMM2023B05)the Natural Science Foundation of Henan Province(No.252300421541)
文摘The development of medium-entropy alloys(MEAs)with superior mechanical properties and remarkable antibacterial performance has garnered significant attention in the field of metallic biomaterials.In this study,Ti-18Zr-8Mo-10Cu MEAs with varying properties,including mechanical properties,corrosion resistance,antibacterial performance,and cytocompatibility,were obtained through heat treatment at 900℃for 1 h,followed by various cooling methods(water cooling,air cooling,and furnace cooling).An increasing cooling rate results in a decrease in the elastic modulus.The water-cooling specimen exhibits optimal ductility over 40%and minimum elastic modulus of 60 GPa.Moreover,the reduction in alloy composition segregation after heat treatment enhances the anticorrosion properties,exhibiting a robust passivation capability of MEAs.All synthesized Ti-18Zr-8Mo-10Cu ME As show favorable cytocompatibility and robust antibacterial rate approaching~100%at 12 and 24 h.Generally,the water-cooling specimen shows exceptional mechanical properties and outstanding antibacterial performance,holding considerable promise for future orthopedic applications.This study offers a viable approach to optimizing the comprehensive properties of copper-bearing Ti MEAs for biomedical applications.
基金supported by the National Research Founda-tion of Korea(NRF)grant funded by the Korean government(MSIT)(Nos.2021R1A2C3006662 and RS-2023-00281246)supported by the Principal R&D project(contract no.PNK9950)of the Korean Institute of Materials Science(KIMS).
文摘Metal additive manufacturing(MAM)enables near-net shape production of components with minimized waste and excellent mechanical performance based on multi-scale microstructural heterogeneity.Espe-cially,the dislocation cell network that often bears elemental segregation or precipitation of a secondary phase contributes to enhancing the strength of additively manufactured materials.The cell boundaries can also act as active nucleation sites for the formation of precipitates under post-MAM heat treatment,as the chemical heterogeneity and profuse dislocations generate a driving force for precipitation.In this work,we subjected a Co_(18)Cr_(15)Fe_(50)Ni_(10)Mo_(6.5)C_(0.5)(at%)medium-entropy alloy fabricated by laser powder bed fusion(LPBF)to post-LPBF annealing at 900℃for 10 min.Microstructural investigation revealed that the cell boundaries of the as-built sample,which were decorated by Mo segregation,are replaced byμphase andM_(6)C typecarbide precipitatesduringannealingwhile thegrainstructureand sizeremain unaffected,indicating that the post-LPBF annealing delivered the proper amount of heat input to alter only the cell structure.The yield strength slightly decreased with annealing due to a reduction in the strengthening effect by the cell boundaries despite an increased precipitation strengthening effect.How-ever,the post-LPBF annealing improved the strain hardenability and the ultimate tensile strength was enhanced from∼1.02 to∼1.15 GPa owing to reinforced back stress hardening by the increased disloca-tion pile-up at the precipitates.Our results suggest that the cell structure with chemical heterogeneity can be successfully controlled by careful post-MAM heat treatment to tailor the mechanical performance,while also providing insight into alloy design for additive manufacturing.
基金financially supported by the National Natural Science Foundation of China(Nos.52071024,52271003 and 52101188)the National Science Fund for Distinguished Young Scholars of China(No.52225103)+2 种基金the Funds for Creative Research Groups of China(No.51921001)the Projects of International Cooperation and Exchanges NSFC(Nos.51961160729 and 52061135207)the Fundamental Research Fund for the Central Universities of China,and the State Key Laboratory for Advanced Metals and Materials.
文摘High/medium entropy alloys(H/MEAs)have shown unique strengthening behavior and mechanical prop-erties because of the presence of massive local chemical orderings.Nevertheless,dynamic interactions between chemical short-range orders(CSROs)and dislocations,and the underlying atomic strengthening mechanism remain elusive.In this work,we first developed a novel machine learning-embedded atom method(ML-EAM)potential of the CoNiV system,trained on a comprehensive first-principles dataset,which enables accurate and efficient modeling of CSRO formation and dislocation dynamics.Then,we in-vestigated the strengthening mechanisms of CSROs in CoNiV MEA through machine learning-augmented molecular dynamics(MD)simulations.Hybrid MD/Monte Carlo simulations reveal that CSRO domains possess an L1_(2)(NiCo)_(3) V structure,whose size increases with lowering annealing temperatures.These domains significantly enhance strength by impeding dislocation motion through complex energy path-ways,increasing depinning forces,and reducing mobility.Moreover,the MD simulations combined with theoretical analysis elucidate the competition between CSRO-assisted strengthening(via antiphase bound-ary formation)and solid solution weakening(via reduced atomic misfit volume).Phonon-drag effects are also amplified by CSROs,further resisting dislocation glide.Our results demonstrate that L1_(2)-CSROs strengthen CoNiV MEA primarily through antiphase boundary and phonon-drag contributions,providing new insights for designing high-performance multi-principal-element alloys via tailoring CSROs.
