Overcoming the strength-ductility trade-off in alloys without complex post-processing remains a critical challenge.Here,we designed a hierarchical heterostructure of micro-cellular segregation(MCS)and supranano precip...Overcoming the strength-ductility trade-off in alloys without complex post-processing remains a critical challenge.Here,we designed a hierarchical heterostructure of micro-cellular segregation(MCS)and supranano precipitates(SNPs)in the directly cast medium-entropy alloy(MEA),achieving higher strength without a significant loss of plasticity.This MCS-SNP alloy exhibits a superior combination of tensile strength(~922 MPa)and elongation(~32%)compared with most traditional ascast face-centered cubic(FCC)alloys.The MCS impedes the movement of the slip bands and maintains the flow stress in the work-hardening process.The SNPs enhance the pinning effect of dislocations,providing an additional source of work hardening together with microbands.The synergistic effect of MCS and SNP generates significant back stress at both micro and nano scales.The findings of this study provide a promising strategy for designing high-performance casting alloys with integrated microscale cellular segregation and supranano precipitate structures.展开更多
The development of cost-effective,strong,and ductile alloys for various temperatures is crucial but challenging for the modern industry.In this study,we designed a series of novel L1_(2)-strengthened(Fe_(58.98)Ni_(31....The development of cost-effective,strong,and ductile alloys for various temperatures is crucial but challenging for the modern industry.In this study,we designed a series of novel L1_(2)-strengthened(Fe_(58.98)Ni_(31.7)Al_(6)Ti_(3)Zr_(0.1)C_(0.2)B_(0.02))_(100-x)Cr_(x)(x=0,4,8,and 13 at%)Fe-based medium-entropy alloys(MEAs).The alloy with 8%Cr content demonstrated optimal mechanical properties from-196℃to 700℃,outperforming numerous MEAs and austenitic stainless steels.At 25℃,it exhibited a yield strength and elongation of~843 MPa and 23%,respectively.Both strength and ductility improved as the temperature decreased from 25℃to-196℃.The excellent mechanical properties at 25℃are attributed to the synergistic effects of L1_(2)nanoprecipitates,dislocations,slip bands,and stacking faults.In the sample deformed at-196℃,Lomer-Cottrell locks were also observed.Furthermore,at 700℃,the MEA maintains a high yield strength of~766 MPa and elongations of 26%,which is attributed to the shearing of L1_(2)precipitate and dislocation slips.This study provides a foundation for developing advanced alloys for use across a wide temperature range.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
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
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
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
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
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
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
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
Electrochemical water splitting has attracted tremendous interest as a promising approach for generating sustainable hydrogen for transportation and other industrial applications.However,the oxygen evolution reaction(...Electrochemical water splitting has attracted tremendous interest as a promising approach for generating sustainable hydrogen for transportation and other industrial applications.However,the oxygen evolution reaction(OER)significantly limits the efficiency of electrochemical water splitting because of the sluggish reaction kinetics derived from the intrinsic four-electron-transfer process.In addition,the stability of OER electrocatalysts encounters significant challenges during long-term operation under harsh conditions.To overcome these challenges,we demonstrate that monolithic electrodes composed of medium-entropy alloys(MEAs)containing Fe,Co,Cr,and Ni can be used as efficient and stable OER catalysts in alkaline solutions.The monolithic FeCoCrNi alloy electrode exhibited a remarkably low overpotential of 237 mV at a current density of 10 mA/cm^(2) in a 1 mol/L KOH solution.Significantly,the monolithic alloy electrode can operate stably for more than 2000 h at a practical current density of 1 A/cm^(2).The enhanced activity and stability of the alloy electrode are ascribed to surface reconstruction.This work presents a novel and effective approach for fabricating high-performance electrodes with excellent stability for the oxygen evolution reaction.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
Face-centered cubic(FCC)equi-atomic multi-principal element alloys(MPEAs)exhibit excellent mechan-ical properties over a broad temperature range from cryogenic temperatures(CTs)to room temperature(RT).Specifically,whi...Face-centered cubic(FCC)equi-atomic multi-principal element alloys(MPEAs)exhibit excellent mechan-ical properties over a broad temperature range from cryogenic temperatures(CTs)to room temperature(RT).Specifically,while the deformation mechanism is dominated solely by dislocation slip at RT,the re-duction in stacking fault energy(SFE)at CTs leads to enhanced strain hardening with deformation twin-ning.This study employs in-situ neutron diffraction to reveal the temperature-dependent deformation be-havior of the FCC/body-centered cubic(BCC)dual-phase(DP)Al7(CoNiV)93 medium-entropy alloy(MEA),which possesses a matrix exhibiting deformation behavior analogous to that of representative equi-atomic MPEAs.Alongside the increased lattice friction stress associated with reduced temperature as a thermal component,deformation twinning at liquid nitrogen temperature(LNT)facilitates dislocation activity in the FCC matrix,leading to additional strain hardening induced by the dynamic Hall-Petch effect.This would give the appearance that the improved strengthening/hardening behaviors at LNT,compared to RT,are primarily attributable to the FCC phase.In contrast,the BCC precipitates are governed solely by dislocation slip for plastic deformation at both 77 K and 298 K,exhibiting a similar trend in dislocation density evolution.Nevertheless,empirical and quantitative findings indicate that the intrinsically high Peierls-Nabarro barriers in the BCC precipitates exhibit pronounced temperature-dependent lattice fric-tion stress,suggesting that the BCC precipitates play a more significant role in the temperature-dependent strengthening/hardening behaviors for the DP-MEA.This study provides a comprehensive understanding of deformation behavior by thoroughly analyzing temperature-dependent strengthening/hardening mech-anisms across various DP-MPEA systems,offering valuable guidelines for future alloy design.展开更多
In recent years,various highly pathogenic viruses have spread worldwide,posing serious threats to human life and property,thus creating an urgent demand for antibacterial structural materials.In this study,we develope...In recent years,various highly pathogenic viruses have spread worldwide,posing serious threats to human life and property,thus creating an urgent demand for antibacterial structural materials.In this study,we developed two types of antibacterial medium-entropy alloys (MEAs):as-cast (Fe_(63.3)Mn_(14)Si_(9.1)Cr_(9.8)C_(3.8))_(88-x)Cu_(12)Ag_(x)(x=2,4 at%)(which do not require antibacterial aging heat treatment) and heat-treated (Fe_(63.3)Mn_(14)Si_(9.1)Cr_(9.8)C_(3.8))_(99.5-x)Cu_(x)Ag_(0.5)(x=2,4 at%)(abbreviated as CuxAg0.5 and Cu12Agx).Both MEA s exhibit in transformation-induced plasticity (TRIP) and twinning-induced plasticity effects,demonstrating outstanding mechanical properties.Compared to 304 stainless steels,these ME As exhibit superior corrosion resistance,with the Cu2Ag0.5alloy performing the best,exhibiting a corrosion current density of 1.022 A·cm^(-2)and a corrosion potential of-0.297 VSCE.The antibacterial rate of the MEAs reached99.9%after 24 h of interaction with Escherichia coli and Staphylococcus aureus,with Cu 12Ag2 achieving 99.9%antimicrobial activity within 6 h,indicating a shorter activation time for antibacterial activity.According to firstprinciples calculations of state density,work function,and surface energy,Cu12Ag2 demonstrated the highest ion release capability,with a work function of 3.7 eV and surface energy of 1.9 J·m^(-2).The electrostatic adsorption of the Xanthium sibiricum bionic structure,characterized by a nanoscale spherical phase within the antibacterial phase with a size less than 350 nm,promotes ion penetration into bacterial cells,enhancing the synergistic effects of ionic,electronic,and catalytic antibacterial mechanisms.This study provides a new approach for designing high-performance alloys that integrate functional and structural properties,offering broad-spectrum,efficient antibacterial applications under load-bearing conditions.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
A single-phase anti-perovskite medium-entropy alloy nitride foams(MEANFs),as innovative materials for electromagnetic wave(EMW)absorption,have been successfully synthesized through the lattice expansion induced by nit...A single-phase anti-perovskite medium-entropy alloy nitride foams(MEANFs),as innovative materials for electromagnetic wave(EMW)absorption,have been successfully synthesized through the lattice expansion induced by nitrogen doping.This achievement notably overcomes the inherent constraints of conventional metal-based absorbers,including low resonance frequency,high conductivity,and elevated density,for the synergistic advantages provided by multimetallic alloys and foams.Microstructural analysis with comprehensive theoretical calculations provides in-depth insights into the formation mechanism,electronic structure,and magnetic moment of MEANFs.Furthermore,deliberate component design along with the foam structure proves to be an effective strategy for enhancing impedance matching and absorption.The results show that the MEANFs exhibit a minimum reflection loss(RL_(min))value of-60.32 dB and a maximum effective absorption bandwidth(EAB_(max))of 5.28 GHz at 1.69 mm.This augmentation of energy dissipation in EMW is predominantly attributed to factors such as porous structure,interfacial polarization,defect-induced polarization,and magnetic resonance.This study demonstrates a facile and efficient approach for synthesizing single-phase medium-entropy alloys,emphasizing their potential as materials for electromagnetic wave absorption due to their adjustable magnetic-dielectric properties.展开更多
基金supported by the National Natural Science Foundation of China(Grant Nos.52401215,52271149,52301209,52401214,52201183)the Shanghai Magnolia Talent Plan Pujiang Project(Grant No.24PJD035)+3 种基金the Open Research Fund of Songshan Lake Materials Laboratory(Grant No.2023SLABFN07)the Technology Plan Program of Shanghai Municipal Commission of Science and Technology(Grant No.25CL2902300)the Shanghai Science and Technology Innovation Action Plan(Grant No.24CL2901500)the Shanghai Municipal Explorer Program(Grant No.25TS1401900)。
文摘Overcoming the strength-ductility trade-off in alloys without complex post-processing remains a critical challenge.Here,we designed a hierarchical heterostructure of micro-cellular segregation(MCS)and supranano precipitates(SNPs)in the directly cast medium-entropy alloy(MEA),achieving higher strength without a significant loss of plasticity.This MCS-SNP alloy exhibits a superior combination of tensile strength(~922 MPa)and elongation(~32%)compared with most traditional ascast face-centered cubic(FCC)alloys.The MCS impedes the movement of the slip bands and maintains the flow stress in the work-hardening process.The SNPs enhance the pinning effect of dislocations,providing an additional source of work hardening together with microbands.The synergistic effect of MCS and SNP generates significant back stress at both micro and nano scales.The findings of this study provide a promising strategy for designing high-performance casting alloys with integrated microscale cellular segregation and supranano precipitate structures.
基金supported by the National Natural Science Foundation of China(Grant Nos.52101053,52371078)。
文摘The development of cost-effective,strong,and ductile alloys for various temperatures is crucial but challenging for the modern industry.In this study,we designed a series of novel L1_(2)-strengthened(Fe_(58.98)Ni_(31.7)Al_(6)Ti_(3)Zr_(0.1)C_(0.2)B_(0.02))_(100-x)Cr_(x)(x=0,4,8,and 13 at%)Fe-based medium-entropy alloys(MEAs).The alloy with 8%Cr content demonstrated optimal mechanical properties from-196℃to 700℃,outperforming numerous MEAs and austenitic stainless steels.At 25℃,it exhibited a yield strength and elongation of~843 MPa and 23%,respectively.Both strength and ductility improved as the temperature decreased from 25℃to-196℃.The excellent mechanical properties at 25℃are attributed to the synergistic effects of L1_(2)nanoprecipitates,dislocations,slip bands,and stacking faults.In the sample deformed at-196℃,Lomer-Cottrell locks were also observed.Furthermore,at 700℃,the MEA maintains a high yield strength of~766 MPa and elongations of 26%,which is attributed to the shearing of L1_(2)precipitate and dislocation slips.This study provides a foundation for developing advanced alloys for use across a wide temperature range.
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.
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 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 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 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supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB0450302)the National Natural Science Foundation of China(Nos.52072358,51902304,22209162,U21A2082)+2 种基金the Fundamental Research Funds for the Central Universities(Nos.YD2060002043,WK2060000048)the Hefei Municipal Natural Science Foundation(No.BJ2060000042)the financial support from the R&D Department of Petro China。
文摘Electrochemical water splitting has attracted tremendous interest as a promising approach for generating sustainable hydrogen for transportation and other industrial applications.However,the oxygen evolution reaction(OER)significantly limits the efficiency of electrochemical water splitting because of the sluggish reaction kinetics derived from the intrinsic four-electron-transfer process.In addition,the stability of OER electrocatalysts encounters significant challenges during long-term operation under harsh conditions.To overcome these challenges,we demonstrate that monolithic electrodes composed of medium-entropy alloys(MEAs)containing Fe,Co,Cr,and Ni can be used as efficient and stable OER catalysts in alkaline solutions.The monolithic FeCoCrNi alloy electrode exhibited a remarkably low overpotential of 237 mV at a current density of 10 mA/cm^(2) in a 1 mol/L KOH solution.Significantly,the monolithic alloy electrode can operate stably for more than 2000 h at a practical current density of 1 A/cm^(2).The enhanced activity and stability of the alloy electrode are ascribed to surface reconstruction.This work presents a novel and effective approach for fabricating high-performance electrodes with excellent stability for the oxygen evolution reaction.
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.
基金supported by the National Research Foundation of Korea(NRF)grant funded by the Korean government(MSIP)(Nos.NRF-2021R1A2C3006662,NRF-2022R1A5A1030054,and RS-2023-00281246)supported by the Basic Science Research Program‘Fostering the Next Generation of Researchers(Ph.D.Candidate)’through the NRF funded by the Ministry of Edu-cation(No.RS-2023-00275651).
文摘Face-centered cubic(FCC)equi-atomic multi-principal element alloys(MPEAs)exhibit excellent mechan-ical properties over a broad temperature range from cryogenic temperatures(CTs)to room temperature(RT).Specifically,while the deformation mechanism is dominated solely by dislocation slip at RT,the re-duction in stacking fault energy(SFE)at CTs leads to enhanced strain hardening with deformation twin-ning.This study employs in-situ neutron diffraction to reveal the temperature-dependent deformation be-havior of the FCC/body-centered cubic(BCC)dual-phase(DP)Al7(CoNiV)93 medium-entropy alloy(MEA),which possesses a matrix exhibiting deformation behavior analogous to that of representative equi-atomic MPEAs.Alongside the increased lattice friction stress associated with reduced temperature as a thermal component,deformation twinning at liquid nitrogen temperature(LNT)facilitates dislocation activity in the FCC matrix,leading to additional strain hardening induced by the dynamic Hall-Petch effect.This would give the appearance that the improved strengthening/hardening behaviors at LNT,compared to RT,are primarily attributable to the FCC phase.In contrast,the BCC precipitates are governed solely by dislocation slip for plastic deformation at both 77 K and 298 K,exhibiting a similar trend in dislocation density evolution.Nevertheless,empirical and quantitative findings indicate that the intrinsically high Peierls-Nabarro barriers in the BCC precipitates exhibit pronounced temperature-dependent lattice fric-tion stress,suggesting that the BCC precipitates play a more significant role in the temperature-dependent strengthening/hardening behaviors for the DP-MEA.This study provides a comprehensive understanding of deformation behavior by thoroughly analyzing temperature-dependent strengthening/hardening mech-anisms across various DP-MPEA systems,offering valuable guidelines for future alloy design.
基金financially supported by the National Natural Science Foundation of China(Nos.12404230 and 52061027)Zhejiang Provincial Natural Science Foundation of China(No.LY23E010002)+2 种基金the Science and Technology Program Project of Gansu Province(Nos.22YF7GA155 and 22ZD6GA008)Lanzhou Youth Science and Technology Talent Innovation Project(No.2023-QN-91)the support from Gansu Provincial Computing Center
文摘In recent years,various highly pathogenic viruses have spread worldwide,posing serious threats to human life and property,thus creating an urgent demand for antibacterial structural materials.In this study,we developed two types of antibacterial medium-entropy alloys (MEAs):as-cast (Fe_(63.3)Mn_(14)Si_(9.1)Cr_(9.8)C_(3.8))_(88-x)Cu_(12)Ag_(x)(x=2,4 at%)(which do not require antibacterial aging heat treatment) and heat-treated (Fe_(63.3)Mn_(14)Si_(9.1)Cr_(9.8)C_(3.8))_(99.5-x)Cu_(x)Ag_(0.5)(x=2,4 at%)(abbreviated as CuxAg0.5 and Cu12Agx).Both MEA s exhibit in transformation-induced plasticity (TRIP) and twinning-induced plasticity effects,demonstrating outstanding mechanical properties.Compared to 304 stainless steels,these ME As exhibit superior corrosion resistance,with the Cu2Ag0.5alloy performing the best,exhibiting a corrosion current density of 1.022 A·cm^(-2)and a corrosion potential of-0.297 VSCE.The antibacterial rate of the MEAs reached99.9%after 24 h of interaction with Escherichia coli and Staphylococcus aureus,with Cu 12Ag2 achieving 99.9%antimicrobial activity within 6 h,indicating a shorter activation time for antibacterial activity.According to firstprinciples calculations of state density,work function,and surface energy,Cu12Ag2 demonstrated the highest ion release capability,with a work function of 3.7 eV and surface energy of 1.9 J·m^(-2).The electrostatic adsorption of the Xanthium sibiricum bionic structure,characterized by a nanoscale spherical phase within the antibacterial phase with a size less than 350 nm,promotes ion penetration into bacterial cells,enhancing the synergistic effects of ionic,electronic,and catalytic antibacterial mechanisms.This study provides a new approach for designing high-performance alloys that integrate functional and structural properties,offering broad-spectrum,efficient antibacterial applications under load-bearing conditions.
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supported by the National Natural Science Foundation of China(Grant No.52071294)the National Key Research and Development Program(Grant No.2022YFE0109800)the Natural Science Foundation of Zhejiang Province(Grant No.LY20E020015).
文摘A single-phase anti-perovskite medium-entropy alloy nitride foams(MEANFs),as innovative materials for electromagnetic wave(EMW)absorption,have been successfully synthesized through the lattice expansion induced by nitrogen doping.This achievement notably overcomes the inherent constraints of conventional metal-based absorbers,including low resonance frequency,high conductivity,and elevated density,for the synergistic advantages provided by multimetallic alloys and foams.Microstructural analysis with comprehensive theoretical calculations provides in-depth insights into the formation mechanism,electronic structure,and magnetic moment of MEANFs.Furthermore,deliberate component design along with the foam structure proves to be an effective strategy for enhancing impedance matching and absorption.The results show that the MEANFs exhibit a minimum reflection loss(RL_(min))value of-60.32 dB and a maximum effective absorption bandwidth(EAB_(max))of 5.28 GHz at 1.69 mm.This augmentation of energy dissipation in EMW is predominantly attributed to factors such as porous structure,interfacial polarization,defect-induced polarization,and magnetic resonance.This study demonstrates a facile and efficient approach for synthesizing single-phase medium-entropy alloys,emphasizing their potential as materials for electromagnetic wave absorption due to their adjustable magnetic-dielectric properties.
