Structural components usually require inexpensive materials with ultrahigh strength,large ductility,and low density,which are still lacking and being searched.We hereby develop a partially recrystallized(Rexed)low-den...Structural components usually require inexpensive materials with ultrahigh strength,large ductility,and low density,which are still lacking and being searched.We hereby develop a partially recrystallized(Rexed)low-density steel having unprecedentedly ultrahigh specific yield strength and large ductility at the same time.The former results from both dislocation hardening in unRexed grains and the significant precipitation hardening of κ-carbides having the sizes of several,tens of and hundreds of nanometers in the Rexed,unRexed grains and at boundaries,respectively.Particularly,the κ-carbides within Rexed grains can grow toward the critical sizes for the maximum cutting-through precipitation hardening during the optimal ageing process,which can be guided by ab initio calculations;consequently,the strength difference between the Rexed and unRexed grains is minimized so that they can deform more compatibly.In addition,the presence of ductile precipitation-free zones close to the discrete intergranular κ-carbides reduces the tendency to the brittle intergranular cracking.A nearly half Rexed microstructure may provide the possibly largest quantity of Rexed/unRexed grain boundaries for the maximum heterodeformation-induced strain-hardening,contributing to large ductility.Therefore,we propose that such a hierarchical precipitation in a nearly half Rexed matrix may be a new microstructural strategy for manufacturing ultrastrong lightweight alloys.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
Dislocation strengthening,as one of the methods to simultaneously enhance the room temperature strength and ductility of alloys,does not achieve the desired strengthening and plasticity effect during elevated-temperat...Dislocation strengthening,as one of the methods to simultaneously enhance the room temperature strength and ductility of alloys,does not achieve the desired strengthening and plasticity effect during elevated-temperature deformation.Here,we report a novel strategy to boost the dislocation multiplication and accumulation during deformation at elevated temperatures through dynamic strain aging(DSA).With the introduction of the rare-earth element Ho in Mg-Y-Zn alloy,Ho atoms diffuse toward dislocations during deformation at elevated temperatures,provoking the DSA effect,which increases the dislocation density significantly via the interactions of mobile dislocations and Ho atoms.The resulting alloy achieves a great enhancement of dislocation hardening and obtains the dual benefits of high strength and good ductility simultaneously at high homologous temperatures.The present work provides an effective strategy to enhancing the strength and ductility for elevated-temperature materials.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
High/medium entropy alloys(H/MEAs)are generally possible to exhibit chemical short-range order(SRO).However,the complex role of SRO on mechanical properties from nano-scale to meso-scale is still challenging so far.He...High/medium entropy alloys(H/MEAs)are generally possible to exhibit chemical short-range order(SRO).However,the complex role of SRO on mechanical properties from nano-scale to meso-scale is still challenging so far.Here,we study the strengthening mechanism and deformation behavior in a model body-centered-cubic HfNbTa MEA by using atomic-scale molecular dynamics,micro-scale dislocation dynamics,and meso-scale crystal plasticity finite element.The SRO inhibits dislocation nucleation at the atomic scale,improving the flow stress.The SRO-induced ultrastrong local stress fluctuation greatly improves the micro-scale dislocation-based strength by the significant dislocation forest strengthening.Moreover,the Ta-rich locally ordered structure leads to an obvious heterogeneous strain and stress partitioning,which forms a strong strain gradient in the adjacent grain interiors and contributes to the strong back-stress-induced strain hardening.展开更多
The design of novel high-entropy alloys(HEAs)provides a unique opportunity for the development of structure-function integrated materials with high mechanical and antimicrobial properties.In this study,by employing th...The design of novel high-entropy alloys(HEAs)provides a unique opportunity for the development of structure-function integrated materials with high mechanical and antimicrobial properties.In this study,by employing the antibacterial effect of copper,a novel Al0.4CoCrCuFeNi HEA with broad-spectrum antibacterial and strong mechanical properties was designed.High concentrations of copper ions released from the HEA prevented growth and biofilm formation by biocorrosive marine bacterial species.These findings serve as a proof-of-concept for further development of unique HEA materials with high antimicrobial efficiency and mechanical properties,compared to conventional antibacterial alloys.展开更多
Contact infection of bacteria and viruses has been a critical threat to human health. The worldwideoutbreak of COVID-19 put forward urgent requirements for the research and development of the selfantibacterial materia...Contact infection of bacteria and viruses has been a critical threat to human health. The worldwideoutbreak of COVID-19 put forward urgent requirements for the research and development of the selfantibacterial materials, especially the antibacterial alloys. Based on the concept of high-entropy alloys, thepresent work designed and prepared a novel Co_(0.4)FeCr_(0.9)Cu_(0.3) antibacterial high-entropy alloy with superior antibacterial properties without intricate or rigorous annealing processes, which outperform the antibacterial stainless steels. The antibacterial tests presented a 99.97% antibacterial rate against Escherichiacoli and a 99.96% antibacterial rate against Staphylococcus aureus after 24 h. In contrast, the classic antibacterial copper-bearing stainless steel only performed the 71.50% and 80.84% antibacterial rate, respectively. The results of the reactive oxygen species analysis indicated that the copper ion release and theimmediate contact with copper-rich phase had a synergistic effect in enhancing antibacterial properties.Moreover, this alloy exhibited excellent corrosion resistance when compared with the classic antibacterialstainless steels, and the compression test indicated the yield strength of the alloy was 1015 MPa. Thesefindings generate fresh insights into guiding the designs of structure-function-integrated antibacterial alloys.展开更多
The high strength is a typical advantage of body-centered-cubic high-entropy alloys(BCC–HEAs).However,brittleness and weak strain-hardening ability are still their Achilles'heel.Here,extraordinary strength togeth...The high strength is a typical advantage of body-centered-cubic high-entropy alloys(BCC–HEAs).However,brittleness and weak strain-hardening ability are still their Achilles'heel.Here,extraordinary strength together with good tensile ductility are achieved in(Zr_(0.5)Ti_(0.35)Nb_(0.15))_(100-x)Al_(x) alloys(at.%,x=10 and 20)at room temperature.Relatively low densities of less than 6 g/cm^(3)are exhibited in these alloys.Designing nanoprecipitates and diversifying dislocation motions are the keys to achieving such salient breakthrough.It is worth noting that the tensile strength of 1.8 GPa in(Zr_(0.5)Ti_(0.35)Nb_(0.15))_(80)Al_(20)alloy is a record-high value known in reported BCC–HEAs,as well as a tensile strain over 8%.Furthermore,the maximum strain of~25%in(Zr_(0.5)Ti_(0.35)Nb_(0.15))_(90)Al_(10)alloy can challenge existing limit value,and is accompanied with a tensile strength of 1.2 GPa.The current work does not only provide novel ultra-strong and tough structural materials with low density,but also sheds new light on designing BCC–HEAs with attractive performances and strain-hardening ability.展开更多
Recently,the eutectic high-entropy alloy(EHEA),AlCoCrFeNi_(2.1),can reach a good balance of strength and ductility.The dual-phase alloy exhibits a eutectic lamellar microstructure with large numbers of interfaces.Howe...Recently,the eutectic high-entropy alloy(EHEA),AlCoCrFeNi_(2.1),can reach a good balance of strength and ductility.The dual-phase alloy exhibits a eutectic lamellar microstructure with large numbers of interfaces.However,the role of the interfaces in plastic deformation have not been revealed deeply.In the present work,the orientation relationship(OR)of the interfaces has been clarified as the Kurdjumov-Sachs(KS)interfaces presenting〈111〉_(B2) 〈110〉_(FCC)and {110} _(B2){111}_(FCC) independent of their morphologies.There exist three kinds of interfaces in the EHEA,namely,The dominating interface and the secondary interface are both non-slip planes and atomistic-scale faceted,facilitating the nucleation and slip transmission of the dislocations.The formation mechanism of the preferred interfaces is revealed using the atomistic geometrical analysis according to the criteria of the low interfacial energy based on the coincidence-site lattice(CSL)theory.In particular,the ductility of the dual-phase alloy originates from the KS interface-induced slip continuity across interfaces,which provides a high slip-transfer geometric factor.Moreover,the strengthening effect can be attributed to the interface resistance for the dislocation transmission due to the mismatches of the moduli and lattice parameters at the interfaces.展开更多
Achieving high strength in Mg alloys is usually accompanied by ductility loss.Here,a novel Mg97Y1Zn1Ho1 at.%alloy with a yield strength of 403 MPa and an elongation of 10%is developed.The strength-ductility synergy is...Achieving high strength in Mg alloys is usually accompanied by ductility loss.Here,a novel Mg97Y1Zn1Ho1 at.%alloy with a yield strength of 403 MPa and an elongation of 10%is developed.The strength-ductility synergy is obtained by a comprehensive strategy,including a lamella bimodal microstructure design and the introduction of nano-spaced solute-segregated 14H long-period stacking-ordered phase(14H LPSO phase)through rare-earth Ho alloying.The lamella bimodal microstructure consists of elongated un-recrystallized(un-DRXed)coarse grains and fine dynamically-recrystallized grains(DRXed regions).The nano-spaced solute-segregated 14H LPSO phase is distributed in DRXed regions.The outstanding yield strength is mainly contributed by grain-boundary strengthening,18R LPSO strengthening,and fiberlike reinforcement strengthening from the nano-spaced 14H LPSO phase.The high elongation is due primarily to the combined effects of the bimodal and lamellar microstructures through enhancing the work-hardening capability.展开更多
The growing need for stronger and more ductile structural materials has spurred an intense search for innovative,high-performance alloys.Traditionally,alloys face a pervasive trade-off:high strength often comes at the...The growing need for stronger and more ductile structural materials has spurred an intense search for innovative,high-performance alloys.Traditionally,alloys face a pervasive trade-off:high strength often comes at the expense of ductility and vice versa.The advent of high-entropy alloys(HEAs)offering both high strength and ductility has transformed this landscape.In this work,we discuss the deformation mechanisms of HEAs,examine the foundations of the strength-ductility trade-off,and explore approaches for designing HEAs to surmount this limitation.Furthermore,we analyze the factors that govern HEA-deformation performance,which in turn influence the HEA design.We also propose a perspective on future research directions concerning the mechanical behavior of HEAs,highlighting potential breakthroughs and novel strategies to advance the field.展开更多
Wire+arc additive manufacturing(WAAM)is considered an innovative technology that can change the manufacturing landscape in the near future.WAAM offers the benefits of inexpensive initial system setup and a high deposi...Wire+arc additive manufacturing(WAAM)is considered an innovative technology that can change the manufacturing landscape in the near future.WAAM offers the benefits of inexpensive initial system setup and a high deposition rate for fabricating medium-and large-sized parts such as die-casting tools.In this study,AISI H13 tool steel,a popular die-casting tool metal,is manufactured by cold metal transfer(CMT)-based WAAM and is then comprehensively analyzed for its microstructural and mechanical properties.Location-dependent phase combinations are observed,which could be explained by nonequilibrium thermal cycles that resulted from the layer-by-layer stacking mechanism used in WAAM.In addition,remelting and reheating of the layers reduces welding anomalies(e.g.,pores and voids).The metallurgical characteristics of the H13 strongly correlate with the mechanical properties.The combinations of phases at different locations of the additively manufactured part exhibit a periodic microhardness profile.Martensite,Retained Austenite,Ferrite,and Carbide phases are found in combination at different locations of the part based on the part’s temperature distribution during additive deposition.Moreover,the tensile properties at elevated temperatures(23℃,300℃,and 600℃)are comparable to those from other WAAM and additive manufacturing(AM)processes.The X-ray diffraction results verify that the microstructural stability of the fabricated parts at high temperatures would allow them to be used in high temperatures.展开更多
In this study,a new Al0.9CoFeNi2 eutectic high entropy alloy(EHEA) was designed,and the microstructures as well as the deformation behavior were investigated.The bulk cast Al0.9CoFeNi2 EHEA exhibited an order face-cen...In this study,a new Al0.9CoFeNi2 eutectic high entropy alloy(EHEA) was designed,and the microstructures as well as the deformation behavior were investigated.The bulk cast Al0.9CoFeNi2 EHEA exhibited an order face-centered cubic FCC(L12) and an order body-centered cubic(B2) dual-phase lamellar eutectic microstructure.The volume fractions of FCC(L12) and B2 phases are measured to be 60 % and 40 %,respectively.The combination of the soft and ductile FCC(L12) phase together with the hard B2 phase resulted in superior strength of 1005 MPa and ductility as high as 6.2 % in tension at room temperature.The Al0.9CoFeNi2 EHEA exhibited obvious three-stage work hardening characteristics and high workhardening ability.The evolving dislocation substructure s during uniaxial tensile deformation found that planar slip dominates in both FCC(L12) and B2 phases,and the FCC(L12) phase is easier to deform than the B2 phase.The post-deformation transmission electron microscopy revealed that the sub-structural evolution of the FCC(L12) phase is from planar dislocations to bending dislocations,high-density dislocations,dislocation network,and then to dislocation walls,and Taylor lattices,while the sub-structural evolution of the B2 phase is from a very small number of short dislocations to a number of planar dislocations.Moreover,obvious ductile fracture in the FCC(L12) phase and a brittle-like fracture in the B2 phase were observed on the fracture surface of the Al0.9CoFeNi2 EHEA.The re search results provide some insight into the microstructure-property relationship.展开更多
A novel cobalt-free oxide dispersion strengthened(ODS)equiatomic FeCrNi medium entropy alloy(MEA)was successfully fabricated through mechanical alloying and hot extrusion(HE).The ODS FeCrNi MEA is composed of a single...A novel cobalt-free oxide dispersion strengthened(ODS)equiatomic FeCrNi medium entropy alloy(MEA)was successfully fabricated through mechanical alloying and hot extrusion(HE).The ODS FeCrNi MEA is composed of a single face-centered cubic(FCC)matrix,in which highly dispersed oxide nanoparticles,including Y_(2)Ti_(2)O_(7),Y_(2)TiO_(5) and Y_(2)O_(3),are uniformly distributed.Compared with the FeCrNi MEA,the ODS FeCrNi MEA exhibits the improved yield strength(1120 MPa)and ultimate tensile strength(1274 MPa)with adequate ductility retention(12.1%).Theoretical analysis of the strengthening mechanism indicates that the high strength is mainly attributed to the grain-boundary strengthening caused by fine grains and the precipitation strengthening resulted from the oxide nanoparticles.Meanwhile,the matrix that easily activates mechanical twinning during the deformation process is the main reason to ensure moderate ductility.In addition,the introduction of high-density oxide nanoparticles can disperse the defect distri-bution and suppress the defect growth and irradiation-induced segregation,leading to the excellent irra-diation resistance.These findings provide innovative guidance for the development of high-performance structural materials for future nuclear energy applications with balanced strength and ductility.展开更多
The mechanical-property improvement of directionally-solidified Nickel-based single crystal(SC)superalloy with the single-direction magnetic fields is limited by their destructiveness on the dendritic microstructure.H...The mechanical-property improvement of directionally-solidified Nickel-based single crystal(SC)superalloy with the single-direction magnetic fields is limited by their destructiveness on the dendritic microstructure.Here,the work present breaks through the bottleneck.It shows that the application of the cusp magnetic field(CMF)ensures that the dendrites are not destroyed.This feature embodies that the primary dendrite trunks arrange regularly and orderly,as well the secondary dendrite arms grow symmetrically.By contrast,both the unidirectional transverse and longitudinal magnetic field destroy the dendrite morphology,and there are a number of stray grains near the totally-re melted interface.The nondestructive effect is achieved mainly by the combined action of the thermoelectromagnetic force on the dendrites and thermoelectromagnetic convection in the melt during directional solidification.The investigation should contribute a new route for dramatically and effectively improving the crystal quality and mechanical properties of the directionally-solidified alloys.展开更多
Over recent years,eutectic high-entropy alloys(EHEAs)have intrigued substantial research enthusiasms due to their good castability as well as balanced strength-ductility synergy.In this study,a bulk cast Al_(19.25)Co_...Over recent years,eutectic high-entropy alloys(EHEAs)have intrigued substantial research enthusiasms due to their good castability as well as balanced strength-ductility synergy.In this study,a bulk cast Al_(19.25)Co_(18.86)Fe_(18.36)Ni_(43.53)EHEA is developed with fine in-situ lamellar eutectics.The eutectics comprise alternating ordered face-centered-cubic(L1_(2))and ordered body-centered-cubic(B2)phases with semicoherent interfaces.The resulting microstructure resembles that of most reported as-cast EHEAs,but the B2 lamellae are devoid of nano-precipitates because of the Cr-element removal in current tailored eutectic composition.Surprisingly,the B2 lamellae still feature much higher deformation resistance than the L1_(2) lamellae,so that less lattice defects are detected in the B2 lamellae until the fracture.More interestingly,in the L1_(2) lamellae we identify a dynamic microstructure refinement that correlates to extraordinary strain hardening in tension.The precipitate-free EHEA consequently shows excellent tensile ductility of~10%and high ultimate strength up to~956 MPa.展开更多
Coherent precipitation of cuboidal γ'-Co3(Al,W) nanoparticles in face-centered-cubic (FCC)-γ matrix is of great significance for improving high-temperature mechanical properties of Co-based superalloys. The pres...Coherent precipitation of cuboidal γ'-Co3(Al,W) nanoparticles in face-centered-cubic (FCC)-γ matrix is of great significance for improving high-temperature mechanical properties of Co-based superalloys. The present work developed a series of low-density Co-based superalloys in light of the cluster composition formula of [Al1-(Co,Ni)12]((Al0.5(Ti/Nb/Ta)0.5W0.5)(Mo0.5Cr0.5Co0.5)), where the addition of Ti, Nb, and Ta is mixed with an equimolar ratio. It is found that these designed alloys with different combinations of Ti/Nb/Ta, Ti/Nb, and Ti/Ta possess the coherent microstructure of cuboidal γ' nanoprecipitates in the FCC-γ matrix. The microstructural evolution of coherent γ/γ' during aging at 1173 K shows that these superalloys exhibit higher thermal stability at high temperatures. Even after aging for 1000 h, there do not exist any other precipitated phases on grain boundaries, except the coarse γ' precipitates. Also, the coarsening rate constants of cuboidal γ' nanoprecipitates in these alloys are very low (K = 5.76-6.03 nm3/s), which is mainly ascribed to a moderate lattice misfit (ε = 0.28 %-0.45 %) between γ and γ'. The stable γ/γ' microstructure renders the alloys with prominent mechanical properties, as evidenced by the high yield strength of σYS = 438-445 MPa at 1143 K. A large amount of stacking faults appear after compressive deformation and Lomer-Contrell dislocation locks are also formed due to the reaction of partial dislocations of stacking faults. Moreover, the microhardness (285-320 HV) in each alloy keeps almost constant with the aging time. Besides, these superalloys have a relatively lower density (8.67-8.89 g/cm3), among which the alloy containing Ti0.25Ta0.25 also exhibits a much higher γ' solvus temperature (1361 ± 2 K) than those of the existing Co-Al-W-based superalloys.展开更多
The gradient nanostructured medium entropy alloys(MEAs) exhibit a good yielding strength and great plasticity. Here, the mechanical properties, microstructure, and strain gradient in the gradient nanostructured MEA Cr...The gradient nanostructured medium entropy alloys(MEAs) exhibit a good yielding strength and great plasticity. Here, the mechanical properties, microstructure, and strain gradient in the gradient nanostructured MEA CrCoNi are studied by atomic simulations. The strong gradient stress and strain always occur in the deformed gradient nanograined MEA CrCoNi. The origin of improving strength is attributed to the formation of the 9 R phase, deformation twinning, as well as the fcc to hcp phase transformation, which prevent strain localization. A microstructure-based predictive model reveals that the lattice distortion dependent solid-solution strengthening and grain-boundary strengthening dominate the yield strength,and the dislocation strengthening governs the strain hardening. The present result provides a fundamental understanding of the gradient nanograined structure and plastic deformation in the gradient nanograined MEA, which gives insights for the design of MEAs with higher strengths.展开更多
基金the National Natural Science Foundation of China(Grant Nos.U2267252,12172123,and 12072109)the Natural Science Foundation of Hunan Province(Grant Nos.2022JJ20001 and 2021JJ40032)+2 种基金the Science and Technology Innovation Program of Hunan Province(Grant No.2022RC1200)the National Science Foundation(Grant Nos.DMR-1611180,1809640,and 2226508)the Army Research Office(Grant Nos.W911NF-13-1-0438 and W911NF-19-2-0049).
基金financially supported by the National Natural Science Foundation of China(Nos.52233018 and 51831002)the U.S.National Science Foundation(No.DMR-1611180,1809640,and 2226508)the Army Research Office(Nos.W911NF-13-1-0438 and W911NF-19-2-0049).
文摘Structural components usually require inexpensive materials with ultrahigh strength,large ductility,and low density,which are still lacking and being searched.We hereby develop a partially recrystallized(Rexed)low-density steel having unprecedentedly ultrahigh specific yield strength and large ductility at the same time.The former results from both dislocation hardening in unRexed grains and the significant precipitation hardening of κ-carbides having the sizes of several,tens of and hundreds of nanometers in the Rexed,unRexed grains and at boundaries,respectively.Particularly,the κ-carbides within Rexed grains can grow toward the critical sizes for the maximum cutting-through precipitation hardening during the optimal ageing process,which can be guided by ab initio calculations;consequently,the strength difference between the Rexed and unRexed grains is minimized so that they can deform more compatibly.In addition,the presence of ductile precipitation-free zones close to the discrete intergranular κ-carbides reduces the tendency to the brittle intergranular cracking.A nearly half Rexed microstructure may provide the possibly largest quantity of Rexed/unRexed grain boundaries for the maximum heterodeformation-induced strain-hardening,contributing to large ductility.Therefore,we propose that such a hierarchical precipitation in a nearly half Rexed matrix may be a new microstructural strategy for manufacturing ultrastrong lightweight alloys.
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supported by the National Key Research and Development Project(2023YFA1609100)the NSFC Funding(U2141207,52171111,52001083)+6 种基金Natural Science Foundation of Heilongjiang(YQ2023E026)China Postdoctoral Science foundation(2024M754149)Postdoctoral Fellowship Program of CPSF(GZC20242192)support from the National Science Foundation(DMR-1611180 and 1809640)with the program directors,DrsHKU Seed Fund for Collaborative Research(#2207101618)support by Croucher Senior Research Fellowship and City U Project(Project No.9229019)Shenzhen Science and Technology Program(Project No.JCYJ20220818101203007)。
文摘Dislocation strengthening,as one of the methods to simultaneously enhance the room temperature strength and ductility of alloys,does not achieve the desired strengthening and plasticity effect during elevated-temperature deformation.Here,we report a novel strategy to boost the dislocation multiplication and accumulation during deformation at elevated temperatures through dynamic strain aging(DSA).With the introduction of the rare-earth element Ho in Mg-Y-Zn alloy,Ho atoms diffuse toward dislocations during deformation at elevated temperatures,provoking the DSA effect,which increases the dislocation density significantly via the interactions of mobile dislocations and Ho atoms.The resulting alloy achieves a great enhancement of dislocation hardening and obtains the dual benefits of high strength and good ductility simultaneously at high homologous temperatures.The present work provides an effective strategy to enhancing the strength and ductility for elevated-temperature materials.
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supported by the National Natural Science Foundation of China(Grant No.12172123)the Natural Science Foundation of Hunan Province(Grant Nos.2022JJ20001 and 2021JJ40032)+3 种基金the Science and Technology Innovation Program of Hunan Province(Grant No.2022RC1200)the Natural Science Foundation of Changsha City(Grant No.kq2202139)the National Science Foundation(Grant Nos.DMR-1611180 and 1809640)the US Army Research Office(Grant Nos.W911NF-13-1-0438 and W911NF-19-2-0049).
基金supported by the National Natural Science Foundation of China(Grant Nos.12372069,12302083,and 12172123)China Postdoctoral Science Foundation(Grant Nos.2023M731061 and BX20230109)+2 种基金the Natural Science Foundation of Hunan Province(Grant No.2022JJ20001)Hunan Provincial Innovation Foundation for Postgraduate(Grant No.CX20220378)Peter K.Liaw very much appreciates the support from the National Science Foundation(Grant Nos.DMR-1611180,1809640,and 2226508).
文摘High/medium entropy alloys(H/MEAs)are generally possible to exhibit chemical short-range order(SRO).However,the complex role of SRO on mechanical properties from nano-scale to meso-scale is still challenging so far.Here,we study the strengthening mechanism and deformation behavior in a model body-centered-cubic HfNbTa MEA by using atomic-scale molecular dynamics,micro-scale dislocation dynamics,and meso-scale crystal plasticity finite element.The SRO inhibits dislocation nucleation at the atomic scale,improving the flow stress.The SRO-induced ultrastrong local stress fluctuation greatly improves the micro-scale dislocation-based strength by the significant dislocation forest strengthening.Moreover,the Ta-rich locally ordered structure leads to an obvious heterogeneous strain and stress partitioning,which forms a strong strain gradient in the adjacent grain interiors and contributes to the strong back-stress-induced strain hardening.
基金the National Natural Science Foundation of China(Nos.51822402 and 51871050)the Fundamental Research Funds for the Central Universities(DUT16ZD206)Dalian Support Plan for Innovation of High-level Talents(Youth Technology Stars,2016RQ005)。
文摘The design of novel high-entropy alloys(HEAs)provides a unique opportunity for the development of structure-function integrated materials with high mechanical and antimicrobial properties.In this study,by employing the antibacterial effect of copper,a novel Al0.4CoCrCuFeNi HEA with broad-spectrum antibacterial and strong mechanical properties was designed.High concentrations of copper ions released from the HEA prevented growth and biofilm formation by biocorrosive marine bacterial species.These findings serve as a proof-of-concept for further development of unique HEA materials with high antimicrobial efficiency and mechanical properties,compared to conventional antibacterial alloys.
基金Supported by the National Key Research and Development Program of China(No.2019YFA0209901)National Natural Science Foundation of China(No.51822402 and U20A20278)+2 种基金Liao Ning Revitalization Talents Program(No.XLYC1807047)Major Special Project of“Scientific and Technological Innovation 2025 in Ningbo(No.2019B10086)Peter K.Liaw thanks the support from the National Science Foundation(DMR-1611180 and 1809640)with the program directors,Drs.Judith Yang,Gary Shiflet,and Diana Farkas.
文摘Contact infection of bacteria and viruses has been a critical threat to human health. The worldwideoutbreak of COVID-19 put forward urgent requirements for the research and development of the selfantibacterial materials, especially the antibacterial alloys. Based on the concept of high-entropy alloys, thepresent work designed and prepared a novel Co_(0.4)FeCr_(0.9)Cu_(0.3) antibacterial high-entropy alloy with superior antibacterial properties without intricate or rigorous annealing processes, which outperform the antibacterial stainless steels. The antibacterial tests presented a 99.97% antibacterial rate against Escherichiacoli and a 99.96% antibacterial rate against Staphylococcus aureus after 24 h. In contrast, the classic antibacterial copper-bearing stainless steel only performed the 71.50% and 80.84% antibacterial rate, respectively. The results of the reactive oxygen species analysis indicated that the copper ion release and theimmediate contact with copper-rich phase had a synergistic effect in enhancing antibacterial properties.Moreover, this alloy exhibited excellent corrosion resistance when compared with the classic antibacterialstainless steels, and the compression test indicated the yield strength of the alloy was 1015 MPa. Thesefindings generate fresh insights into guiding the designs of structure-function-integrated antibacterial alloys.
基金supports from National Natural Science Foundation of China(NSFC,Granted Nos.51671020)Guangdong Basic and Applied Basic Research Foundation(No.2019B1515120020)+2 种基金Creative Research Groups of China(No.51921001)supports from the U.S.Army Office Project(W911NF-13-1-0438 and W911NF-19-2-0049)the National Science Foundation(Nos.DMR1611180 and 1809640)。
文摘The high strength is a typical advantage of body-centered-cubic high-entropy alloys(BCC–HEAs).However,brittleness and weak strain-hardening ability are still their Achilles'heel.Here,extraordinary strength together with good tensile ductility are achieved in(Zr_(0.5)Ti_(0.35)Nb_(0.15))_(100-x)Al_(x) alloys(at.%,x=10 and 20)at room temperature.Relatively low densities of less than 6 g/cm^(3)are exhibited in these alloys.Designing nanoprecipitates and diversifying dislocation motions are the keys to achieving such salient breakthrough.It is worth noting that the tensile strength of 1.8 GPa in(Zr_(0.5)Ti_(0.35)Nb_(0.15))_(80)Al_(20)alloy is a record-high value known in reported BCC–HEAs,as well as a tensile strain over 8%.Furthermore,the maximum strain of~25%in(Zr_(0.5)Ti_(0.35)Nb_(0.15))_(90)Al_(10)alloy can challenge existing limit value,and is accompanied with a tensile strength of 1.2 GPa.The current work does not only provide novel ultra-strong and tough structural materials with low density,but also sheds new light on designing BCC–HEAs with attractive performances and strain-hardening ability.
基金supported financially by the National Natural Science Foundation of China(No.51771201 and No.51822402)the Key Project of Natural Science Foundation of Liaoning Province+4 种基金China(No.20180510059)the Shenyang National Laboratory for Materials Science(No.2017RP17)the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University(No.SKLSP201902)support of the U.S.Army Research Office Project(W911NF-13-1-0438 and W911NF-19-2-0049)with the program managers,Drs.M.P.Bakas,S.N.Mathaudhu,D.M.Steppsupport from the National Science Foundation(DMR-1611180 and DMR-1809640)with the program directors,Drs.J.Yang,G.Shiflet,D.Farkas。
文摘Recently,the eutectic high-entropy alloy(EHEA),AlCoCrFeNi_(2.1),can reach a good balance of strength and ductility.The dual-phase alloy exhibits a eutectic lamellar microstructure with large numbers of interfaces.However,the role of the interfaces in plastic deformation have not been revealed deeply.In the present work,the orientation relationship(OR)of the interfaces has been clarified as the Kurdjumov-Sachs(KS)interfaces presenting〈111〉_(B2) 〈110〉_(FCC)and {110} _(B2){111}_(FCC) independent of their morphologies.There exist three kinds of interfaces in the EHEA,namely,The dominating interface and the secondary interface are both non-slip planes and atomistic-scale faceted,facilitating the nucleation and slip transmission of the dislocations.The formation mechanism of the preferred interfaces is revealed using the atomistic geometrical analysis according to the criteria of the low interfacial energy based on the coincidence-site lattice(CSL)theory.In particular,the ductility of the dual-phase alloy originates from the KS interface-induced slip continuity across interfaces,which provides a high slip-transfer geometric factor.Moreover,the strengthening effect can be attributed to the interface resistance for the dislocation transmission due to the mismatches of the moduli and lattice parameters at the interfaces.
基金supported by the National Key Research and Development Project (2018YFE0115800, 2020YFE0202600)Youth Talent Project of China National Nuclear Corporation (CNNC2019YTEP-HEU01, CNNC2021YTEP-HEU01)+4 种基金the NSFC Funding (51701051, 52001083, 52171111, U2141207)China Postdoctoral Science Foundation Funded Project (2019T120255)Natural Science Foundation of Heilongjiang (LH2019E030)Heilongjiang Touyan Innovation Team Programthe supports from the U.S. National Science Foundation [DMR-1611180 and 1809640] with the program directors, Drs. Judith Yang, Gary Shiflet, and Diana Farkas.
文摘Achieving high strength in Mg alloys is usually accompanied by ductility loss.Here,a novel Mg97Y1Zn1Ho1 at.%alloy with a yield strength of 403 MPa and an elongation of 10%is developed.The strength-ductility synergy is obtained by a comprehensive strategy,including a lamella bimodal microstructure design and the introduction of nano-spaced solute-segregated 14H long-period stacking-ordered phase(14H LPSO phase)through rare-earth Ho alloying.The lamella bimodal microstructure consists of elongated un-recrystallized(un-DRXed)coarse grains and fine dynamically-recrystallized grains(DRXed regions).The nano-spaced solute-segregated 14H LPSO phase is distributed in DRXed regions.The outstanding yield strength is mainly contributed by grain-boundary strengthening,18R LPSO strengthening,and fiberlike reinforcement strengthening from the nano-spaced 14H LPSO phase.The high elongation is due primarily to the combined effects of the bimodal and lamellar microstructures through enhancing the work-hardening capability.
基金the financial support from the National Natural Science Foundation of China(Nos.52101189 and 52273280)the National Key R&D Program of China(No.2020YFA0405700)+3 种基金The present work was also supported by the Chinese Postdoctoral Science Foundation(No.2020M680343)the Fundamental Research Funds for the Central Universities(No.FRF-TP-20-050A1)PKL thanks the support from the National Science Foundation(Nos.DMR-1611180,1809640,and 2226508)the Army Research Office(Nos.W911NF-13-1-0438 and W911NF-19-2-0049).
文摘The growing need for stronger and more ductile structural materials has spurred an intense search for innovative,high-performance alloys.Traditionally,alloys face a pervasive trade-off:high strength often comes at the expense of ductility and vice versa.The advent of high-entropy alloys(HEAs)offering both high strength and ductility has transformed this landscape.In this work,we discuss the deformation mechanisms of HEAs,examine the foundations of the strength-ductility trade-off,and explore approaches for designing HEAs to surmount this limitation.Furthermore,we analyze the factors that govern HEA-deformation performance,which in turn influence the HEA design.We also propose a perspective on future research directions concerning the mechanical behavior of HEAs,highlighting potential breakthroughs and novel strategies to advance the field.
基金support of the Korea Institute of Industrial Technology as a project on the development of metal 3D printing materials and process optimization technology for medium-and large-sized transportation part mold manufacturing(KITECH JE200008)。
文摘Wire+arc additive manufacturing(WAAM)is considered an innovative technology that can change the manufacturing landscape in the near future.WAAM offers the benefits of inexpensive initial system setup and a high deposition rate for fabricating medium-and large-sized parts such as die-casting tools.In this study,AISI H13 tool steel,a popular die-casting tool metal,is manufactured by cold metal transfer(CMT)-based WAAM and is then comprehensively analyzed for its microstructural and mechanical properties.Location-dependent phase combinations are observed,which could be explained by nonequilibrium thermal cycles that resulted from the layer-by-layer stacking mechanism used in WAAM.In addition,remelting and reheating of the layers reduces welding anomalies(e.g.,pores and voids).The metallurgical characteristics of the H13 strongly correlate with the mechanical properties.The combinations of phases at different locations of the additively manufactured part exhibit a periodic microhardness profile.Martensite,Retained Austenite,Ferrite,and Carbide phases are found in combination at different locations of the part based on the part’s temperature distribution during additive deposition.Moreover,the tensile properties at elevated temperatures(23℃,300℃,and 600℃)are comparable to those from other WAAM and additive manufacturing(AM)processes.The X-ray diffraction results verify that the microstructural stability of the fabricated parts at high temperatures would allow them to be used in high temperatures.
基金supported financially by the National Natural Science Foundation of China(Nos.51901116,51822402 and 51671044)the National Key Research and Development Program of China(Nos.2019YFA0209901 and 2018YFA0702901)+5 种基金the Fund of the State Key Laboratory of Solidification Processing in NWPU(No.SKLSP201902)the Liao Ning Revitalization TalentsProgram(No.XLYC1807047)the National MCF Energy R&D Program(No.2018YFE0312400)the Fund of Science and Technology on Reactor Fuel and Materials Laboratory(No.STRFML-2020-04)the U.S.Army Research Office for the support of the present work through projects Nos.W911NF-13-1-0438 and W911NF-19-2-0049the National Science Foundation for the support of the present work through projects Nos.DMR1611180 and 1809640。
文摘In this study,a new Al0.9CoFeNi2 eutectic high entropy alloy(EHEA) was designed,and the microstructures as well as the deformation behavior were investigated.The bulk cast Al0.9CoFeNi2 EHEA exhibited an order face-centered cubic FCC(L12) and an order body-centered cubic(B2) dual-phase lamellar eutectic microstructure.The volume fractions of FCC(L12) and B2 phases are measured to be 60 % and 40 %,respectively.The combination of the soft and ductile FCC(L12) phase together with the hard B2 phase resulted in superior strength of 1005 MPa and ductility as high as 6.2 % in tension at room temperature.The Al0.9CoFeNi2 EHEA exhibited obvious three-stage work hardening characteristics and high workhardening ability.The evolving dislocation substructure s during uniaxial tensile deformation found that planar slip dominates in both FCC(L12) and B2 phases,and the FCC(L12) phase is easier to deform than the B2 phase.The post-deformation transmission electron microscopy revealed that the sub-structural evolution of the FCC(L12) phase is from planar dislocations to bending dislocations,high-density dislocations,dislocation network,and then to dislocation walls,and Taylor lattices,while the sub-structural evolution of the B2 phase is from a very small number of short dislocations to a number of planar dislocations.Moreover,obvious ductile fracture in the FCC(L12) phase and a brittle-like fracture in the B2 phase were observed on the fracture surface of the Al0.9CoFeNi2 EHEA.The re search results provide some insight into the microstructure-property relationship.
基金This work was supported by the National Natural Science Foun-dation of China(Nos.52020105013 and 52104365)the US National Science Foundation(Nos.DMR 1611180 and 1809640)with program directors,Drs.J.Yang,G.Shiflet,and D.Farkas.
文摘A novel cobalt-free oxide dispersion strengthened(ODS)equiatomic FeCrNi medium entropy alloy(MEA)was successfully fabricated through mechanical alloying and hot extrusion(HE).The ODS FeCrNi MEA is composed of a single face-centered cubic(FCC)matrix,in which highly dispersed oxide nanoparticles,including Y_(2)Ti_(2)O_(7),Y_(2)TiO_(5) and Y_(2)O_(3),are uniformly distributed.Compared with the FeCrNi MEA,the ODS FeCrNi MEA exhibits the improved yield strength(1120 MPa)and ultimate tensile strength(1274 MPa)with adequate ductility retention(12.1%).Theoretical analysis of the strengthening mechanism indicates that the high strength is mainly attributed to the grain-boundary strengthening caused by fine grains and the precipitation strengthening resulted from the oxide nanoparticles.Meanwhile,the matrix that easily activates mechanical twinning during the deformation process is the main reason to ensure moderate ductility.In addition,the introduction of high-density oxide nanoparticles can disperse the defect distri-bution and suppress the defect growth and irradiation-induced segregation,leading to the excellent irra-diation resistance.These findings provide innovative guidance for the development of high-performance structural materials for future nuclear energy applications with balanced strength and ductility.
基金financially supported by the National Natural Science Foundation of China(No.51871142)。
文摘The mechanical-property improvement of directionally-solidified Nickel-based single crystal(SC)superalloy with the single-direction magnetic fields is limited by their destructiveness on the dendritic microstructure.Here,the work present breaks through the bottleneck.It shows that the application of the cusp magnetic field(CMF)ensures that the dendrites are not destroyed.This feature embodies that the primary dendrite trunks arrange regularly and orderly,as well the secondary dendrite arms grow symmetrically.By contrast,both the unidirectional transverse and longitudinal magnetic field destroy the dendrite morphology,and there are a number of stray grains near the totally-re melted interface.The nondestructive effect is achieved mainly by the combined action of the thermoelectromagnetic force on the dendrites and thermoelectromagnetic convection in the melt during directional solidification.The investigation should contribute a new route for dramatically and effectively improving the crystal quality and mechanical properties of the directionally-solidified alloys.
基金financial support from the National Key Research and Development Program of China(Nos.2018YFF0109404,2016YFB0300401 and 2016YFB0301401)the National Natural Science Foundation of China(Nos.U1732276 and U1860202)+4 种基金financial support from the National Natural Science Foundation of China(No.51704193)financial support from the National Natural Science Foundation of China(No.52004156)financial support from the National Natural Science Foundation of China(No.51904184)the supports from the National Science Foundation(DMR-1611180)the US Army Research Office(W911NF-19-2-0049)。
文摘Over recent years,eutectic high-entropy alloys(EHEAs)have intrigued substantial research enthusiasms due to their good castability as well as balanced strength-ductility synergy.In this study,a bulk cast Al_(19.25)Co_(18.86)Fe_(18.36)Ni_(43.53)EHEA is developed with fine in-situ lamellar eutectics.The eutectics comprise alternating ordered face-centered-cubic(L1_(2))and ordered body-centered-cubic(B2)phases with semicoherent interfaces.The resulting microstructure resembles that of most reported as-cast EHEAs,but the B2 lamellae are devoid of nano-precipitates because of the Cr-element removal in current tailored eutectic composition.Surprisingly,the B2 lamellae still feature much higher deformation resistance than the L1_(2) lamellae,so that less lattice defects are detected in the B2 lamellae until the fracture.More interestingly,in the L1_(2) lamellae we identify a dynamic microstructure refinement that correlates to extraordinary strain hardening in tension.The precipitate-free EHEA consequently shows excellent tensile ductility of~10%and high ultimate strength up to~956 MPa.
基金financially supported by the National Natural Science Foundation of China(Nos.52171152,91860108 and U1867201)the Key Discipline and Major Project of Dalian Science and Technology Innovation Foundation(No.2020JJ25CY004)+1 种基金Guangxi Key Laboratory of Information Laboratory Foundation(No.221013-K)Peter K.Liaw very much appreciates the support from the National Science Foundation(Nos.DMR-1611180,1809640,and 2226508).
文摘Coherent precipitation of cuboidal γ'-Co3(Al,W) nanoparticles in face-centered-cubic (FCC)-γ matrix is of great significance for improving high-temperature mechanical properties of Co-based superalloys. The present work developed a series of low-density Co-based superalloys in light of the cluster composition formula of [Al1-(Co,Ni)12]((Al0.5(Ti/Nb/Ta)0.5W0.5)(Mo0.5Cr0.5Co0.5)), where the addition of Ti, Nb, and Ta is mixed with an equimolar ratio. It is found that these designed alloys with different combinations of Ti/Nb/Ta, Ti/Nb, and Ti/Ta possess the coherent microstructure of cuboidal γ' nanoprecipitates in the FCC-γ matrix. The microstructural evolution of coherent γ/γ' during aging at 1173 K shows that these superalloys exhibit higher thermal stability at high temperatures. Even after aging for 1000 h, there do not exist any other precipitated phases on grain boundaries, except the coarse γ' precipitates. Also, the coarsening rate constants of cuboidal γ' nanoprecipitates in these alloys are very low (K = 5.76-6.03 nm3/s), which is mainly ascribed to a moderate lattice misfit (ε = 0.28 %-0.45 %) between γ and γ'. The stable γ/γ' microstructure renders the alloys with prominent mechanical properties, as evidenced by the high yield strength of σYS = 438-445 MPa at 1143 K. A large amount of stacking faults appear after compressive deformation and Lomer-Contrell dislocation locks are also formed due to the reaction of partial dislocations of stacking faults. Moreover, the microhardness (285-320 HV) in each alloy keeps almost constant with the aging time. Besides, these superalloys have a relatively lower density (8.67-8.89 g/cm3), among which the alloy containing Ti0.25Ta0.25 also exhibits a much higher γ' solvus temperature (1361 ± 2 K) than those of the existing Co-Al-W-based superalloys.
基金supported financially by the Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No. 51621004)the National Natural Science Foundation of China (Nos. 51871092, 11772122 and 51771233)+2 种基金the State Key Laboratory of Advanced Design and Manufacturing for Vehicle Body (No. 71865015)the National Key Research and Development Program of China (Nos. 2016YFB0700300 and 2016YFB1100103)the Hunan Provincial Innovation Foundation For Postgraduate (No. CX2018B156)。
文摘The gradient nanostructured medium entropy alloys(MEAs) exhibit a good yielding strength and great plasticity. Here, the mechanical properties, microstructure, and strain gradient in the gradient nanostructured MEA CrCoNi are studied by atomic simulations. The strong gradient stress and strain always occur in the deformed gradient nanograined MEA CrCoNi. The origin of improving strength is attributed to the formation of the 9 R phase, deformation twinning, as well as the fcc to hcp phase transformation, which prevent strain localization. A microstructure-based predictive model reveals that the lattice distortion dependent solid-solution strengthening and grain-boundary strengthening dominate the yield strength,and the dislocation strengthening governs the strain hardening. The present result provides a fundamental understanding of the gradient nanograined structure and plastic deformation in the gradient nanograined MEA, which gives insights for the design of MEAs with higher strengths.
