A newly designed TiAl alloy containing W,Nb,and B was produced through magnetic-flotation-melting method.Mass production of this TiAl-based alloy,15 kg ingot size,which is quite different from the 0.05 kg small ingot ...A newly designed TiAl alloy containing W,Nb,and B was produced through magnetic-flotation-melting method.Mass production of this TiAl-based alloy,15 kg ingot size,which is quite different from the 0.05 kg small ingot produced by arc-melting,has a large effect on the metallurgical properties,such as the grain size and the phase structures of the alloy.Heat treatments were carefully designed in order to reduce the amount of the high-temperature remaining β phase in the alloy,and to obtain optimal microstructures for mechanical behavior studies.A room-temperature ductility of 1.9% was obtained in the cast TiAl-based alloy after the appropriate heat treatment.The mechanical behavior of the large ingot through mass production of the TiAl-based alloy was largely improved by the alloy design and subsequent heat treatments.展开更多
The tribological behavior of Al0.25 CoCrFeNi high-entropy alloy(HEA) sliding against Si3N4 ball was investigated from room temperature to 600°. The microstructure of the alloys was characterized by simple FCC pha...The tribological behavior of Al0.25 CoCrFeNi high-entropy alloy(HEA) sliding against Si3N4 ball was investigated from room temperature to 600°. The microstructure of the alloys was characterized by simple FCC phase with 260 HV. Below 300°, with increasing temperature, the wear rate increased due to high temperature softening. The wear rate remained stabilized above 300°due to the anti-wear effect of the oxidation film on the contact interface. The dominant wear mechanism of HEA changed from abrasive wear at room temperature to delamination wear at 200°, then delamination wear and oxidative wear at 300°and became oxidative above 300°. Moreover, the adhesive wear existed concomitantly below 300°.展开更多
There is currently a gap in our understanding of mechanisms that contribute to high strength and high plasticity in high strength UFG ferritic steel with nano-size Fe3 C carbides in situations that involve combination...There is currently a gap in our understanding of mechanisms that contribute to high strength and high plasticity in high strength UFG ferritic steel with nano-size Fe3 C carbides in situations that involve combination of various strain rates and high temperature.In this regard,we describe the mechanistic basis of obtaining high strength-high plasticity combination in an ultrafine-grained(UFG)(~500±30 nm)ferritic steel with nano-size carbides,which sustained large plastic deformation,exceeding 100%elongation at a temperature significantly below 0.5 of the absolute melting point(Tm).To address the missing gap in our knowledge,we conducted a series of experiments involving combination of strain rate and temperature effects in conjunction with electron microscopy and atom probe tomography(APT).Strain rate studies were carried out at strain rates in the range of 0.0017-0.17 s^(-1)and at different temperatures from 25℃to 600℃.Dynamic recrystallization occurred at 600℃,resulting in a significant decrease in yield and tensile strength.Nevertheless,the UFG ferritic steels had an advantage in tensile strength(UTS)and elongation-to-failure(εf)at 600℃,especially at strain rate of 0.0017 s^(-1),with high UTSof 510 MPa and excellent low temperature(<0.42 Tm)superplasticity(εf=110%).These mechanical properties are significantly superior compared to similar type of steels at identical temperature.A mechanistic understanding of mechanical behavior of UFG ferritic steels is presented by combining the effect of strain rate,temperature,and nano-size carbides.展开更多
The precipitate morphologies,coarsening kinetics,elemental partitioning behaviors,grain structures,and tensile properties were explored in detail for L1_(2)-strengthened Ni_(39.9)Co_(20)Fe_(15)Cr_(15)Al_(6)Ti_(4-x)Nb_...The precipitate morphologies,coarsening kinetics,elemental partitioning behaviors,grain structures,and tensile properties were explored in detail for L1_(2)-strengthened Ni_(39.9)Co_(20)Fe_(15)Cr_(15)Al_(6)Ti_(4-x)Nb_(x)B_(0.1)(x=0 at.%,2 at.%,and 4 at.%)high-entropy alloys(HEAs).By substituting Ti with Nb,the spheroidal-to-cuboidal precipitate morphological transition,increase in the coarsening kinetics,and phase decomposition upon aging at 800°C occurred.The excessive addition of Nb brings about the grain boundary precipitation of an Nb-rich phase along with the phase decomposition from the L1_(2)to lamellar-structured D019 phase upon the long-term aging duration.By partially substituting Ti with Nb,the chemically complex and thermally stable L12 phase with a composition of(Ni_(58.8)Co_(9.8)Fe_(2.7))(Al_(12.7)Ti_(5.8)Nb_(7.5)Cr_(2.3))ensures the stable phase structure and clean grain boundaries,which guarantees the superb high-temperature mechanical properties(791±7 MPa for yielding and 1013±11 MPa for failure)at 700℃.Stacking faults(SFs)were observed to prevail during the plastic deformation,offering a high work-hardening capability at 700°C.An anomalous rise in the yield strength at 800℃was found,which could be ascribed to the multi-layered super-partial dislocations with a cross-slip configuration within the L1_(2)particles.展开更多
To accelerate the exploration,screening,and discovery of structural high-entropy alloys with targeted properties,the newly developed High-Throughput Hot-Isostatic-Pressing based Micro-Synthesis Approach(HT-HIP-MSA)is ...To accelerate the exploration,screening,and discovery of structural high-entropy alloys with targeted properties,the newly developed High-Throughput Hot-Isostatic-Pressing based Micro-Synthesis Approach(HT-HIP-MSA)is employed to efficiently synthesize and characterize 85 combinatorial alloys in a 13-principal element alloying space.These Co Cr Fe Ni-based high entropy alloys span 1 quaternary,9 quinary,and 36 senary alloy systems,and their composition-structure-property relationships are characterized and analyzed experimentally and computationally.From the single-phase FCC CoCrFeNi alloy base,with Mn,Cu,Ti,Nb,Ta,Mo,W,Al,and Si as principal element alloying additions,we find(1)the extended Mn solubility in the single-phase FCC CoCrFeNi-Mn_(x) alloys,(2)the destabilizing behavior for most of the quinary and senary alloys,and(3)the distinctive solid-solution-strengthening effects in the alloys.In combining the computational methods,the HT-HIP-MSA can be systematic and economic to explore and refine the compositions,structures,and properties of structural high-entropy alloys.展开更多
High entropy alloys(HEAs)attract remarkable attention due to the excellent mechanical performance.However,the origins of their high strength and toughness compared with those of the traditional alloys are still hardly...High entropy alloys(HEAs)attract remarkable attention due to the excellent mechanical performance.However,the origins of their high strength and toughness compared with those of the traditional alloys are still hardly revealed.Here,using a microstructure-based constitutive model and molecular dynamics(MD)simulation,we investigate the unique mechanical behavior and microstructure evolution of FeCoCrNiCu HEAs during the indentation.Due to the interaction between the dislocation and solution,the high dislocation density in FeCoCrNiCu leads to strong work hardening.Plentiful slip systems are stimulated,leading to the good plasticity of FeCoCrNiCu.The plastic deformation of FeCoCrNiCu is basically affected by the motion of dislocation loops.The prismatic dislocation loops inside FeCoCrNiCu are formed by the dislocations with the Burgers vectors of a/6[112]and a/6[112],which interact with each other,and then emit along the<111>slip direction.In addition,the mechanical properties of FeCoCrNiCu HEA can be predicted by constructing the microstructure-based constitutive model,which is identified according to the evolution of the dislocation density and the stress-strain curve.Strong dislocation strengthening and remarkable lattice distortion strengthening occur in the deformation process of FeCoCrNiCu,and improve the strength.Therefore,the origins of high strength and high toughness in FeCoCrNiCu HEAs come from lattice distortion strengthening and the more activable slip systems compared with Cu.These results accelerate the discovery of HEAs with excellent mechanical properties,and provide a valuable reference for the industrial application of HEAs.展开更多
Grain boundaries(GBs)can serve as effective sinks for radiation-induced defects,thus notably influencing the service performance of materials.However,the effect of GB structures on the zero-dimensional defects induced...Grain boundaries(GBs)can serve as effective sinks for radiation-induced defects,thus notably influencing the service performance of materials.However,the effect of GB structures on the zero-dimensional defects induced by irradiation has not been fully elucidated.Here,the evolution of cascade collision in the single-crystal(SC),bicrystalline(BC),and twinned crystalline(TC)copper is studied by atomic simulations during irradiation.The spatial distributions of vacancies and interstitials are closely related to the GB at a certain primary knock-on atom(PKA)energy.Compared with the TC,the BC displays a more obvious segregation of the interstitial atoms near GB,due to the characteristic of the greater interstitial binding energy.The evolution of Frenkel pairs is more sensitive to the change of the GB position in the BC.A more prominent defect annihilation rate is caused by the effect of the GB than that of the twin boundary(TB).The marked secondary emission phenomenon has been observed in the BC,which promotes the formation of an inverted pagoda-like defect distribution.There are similar sub-conical defect distributions and microstructures induced by cascade collision in the TC and the SC.It has been found that the influence range of the GB is wider in the BC.Meanwhile,the average flow stress of the irradiated copper is quantitatively calculated by establishing a physical strengthening model.The contribution of vacancy to the average flow stress in the irradiated BC and TC is obvious than that in the SC,due to the formation of many vacancies.This study provides a theoretical basis for further understanding and customization of the metal-based equipment with good radiation resistance.展开更多
By means of rapid heating cyclic heat treatment, the microstructure of a TiAl-based alloy was refined. The colony size and lamellar spacing were measured to be 50 μm and 0.12 μm, respectively. The compression mechan...By means of rapid heating cyclic heat treatment, the microstructure of a TiAl-based alloy was refined. The colony size and lamellar spacing were measured to be 50 μm and 0.12 μm, respectively. The compression mechanical properties were determined at room temperature and the best comprehensive mechanical properties can reach σ0.2 of 745.1 MPa, σp of 1 672.2 MPa and δ of 19.40%. The improvement of mechanical properties is caused by the microstructural refinement and the phase interface nucleation contributes a lot to the refinement of microstructure.展开更多
This paper presents a bilinear log model,for predicting temperature-dependent ultimate strength of high-entropy alloys(HEAs)based on 21 HEA compositions.We consider the break temperature,Tbreak,introduced in the model...This paper presents a bilinear log model,for predicting temperature-dependent ultimate strength of high-entropy alloys(HEAs)based on 21 HEA compositions.We consider the break temperature,Tbreak,introduced in the model,an important parameter for design of materials with attractive high-temperature properties,one warranting inclusion in alloy specifications.For reliable operation,the operating temperature of alloys may need to stay below Tbreak.We introduce a technique of global optimization,one enabling concurrent optimization of model parameters over low-temperature and high-temperature regimes.Furthermore,we suggest a general framework for joint optimization of alloy properties,capable of accounting for physics-based dependencies,and show how a special case can be formulated to address the identification of HEAs offering attractive ultimate strength.We advocate for the selection of an optimization technique suitable for the problem at hand and the data available,and for properly accounting for the underlying sources of variations.展开更多
基金Project(11X-SP173V) supported by the U.S. Fossil Energy Materials ProgramProject supported by the U.S. National Science Foundation Combined Research-Curriculum Development(CRCD) ProgramProject(DE-AC05-00OR-22725 UT-Battelle,LLC) supported by Division of Materials Science and Engineering,Office of Basic Energy Science,U.S.Department of Energy
文摘A newly designed TiAl alloy containing W,Nb,and B was produced through magnetic-flotation-melting method.Mass production of this TiAl-based alloy,15 kg ingot size,which is quite different from the 0.05 kg small ingot produced by arc-melting,has a large effect on the metallurgical properties,such as the grain size and the phase structures of the alloy.Heat treatments were carefully designed in order to reduce the amount of the high-temperature remaining β phase in the alloy,and to obtain optimal microstructures for mechanical behavior studies.A room-temperature ductility of 1.9% was obtained in the cast TiAl-based alloy after the appropriate heat treatment.The mechanical behavior of the large ingot through mass production of the TiAl-based alloy was largely improved by the alloy design and subsequent heat treatments.
基金the opening project from National Key Laboratory for Remanufacturing (No. 61420050204)the Department of Energy (DOE), Office of Fossil Energy, National Energy Technology Laboratory (DE-FE-0011194), with Mr. V. Cedro, Mr. R. Dunst, and Dr. J. Mullen as program managers+1 种基金the support of the U.S. Army Research Office project (W911NF-13-1-0438) with the program manager, Dr. M. P. Bakas and Dr. D. M. Steppsupport from the National Science Foundation (DMR-1611180) with the program directors, Dr. G. J. Shiflet and D. Farkas
文摘The tribological behavior of Al0.25 CoCrFeNi high-entropy alloy(HEA) sliding against Si3N4 ball was investigated from room temperature to 600°. The microstructure of the alloys was characterized by simple FCC phase with 260 HV. Below 300°, with increasing temperature, the wear rate increased due to high temperature softening. The wear rate remained stabilized above 300°due to the anti-wear effect of the oxidation film on the contact interface. The dominant wear mechanism of HEA changed from abrasive wear at room temperature to delamination wear at 200°, then delamination wear and oxidative wear at 300°and became oxidative above 300°. Moreover, the adhesive wear existed concomitantly below 300°.
基金financially supported by the Natural Science Foundation of China(No.51922026)the Fundamental Research Funds for the Central Universities(Nos.N2002013 and N2002005)the support from the National Science Foundation(Nos.DMR-1611180 and 1809640)with the program directors,Drs.G.Shiflet and D.Farkas。
文摘There is currently a gap in our understanding of mechanisms that contribute to high strength and high plasticity in high strength UFG ferritic steel with nano-size Fe3 C carbides in situations that involve combination of various strain rates and high temperature.In this regard,we describe the mechanistic basis of obtaining high strength-high plasticity combination in an ultrafine-grained(UFG)(~500±30 nm)ferritic steel with nano-size carbides,which sustained large plastic deformation,exceeding 100%elongation at a temperature significantly below 0.5 of the absolute melting point(Tm).To address the missing gap in our knowledge,we conducted a series of experiments involving combination of strain rate and temperature effects in conjunction with electron microscopy and atom probe tomography(APT).Strain rate studies were carried out at strain rates in the range of 0.0017-0.17 s^(-1)and at different temperatures from 25℃to 600℃.Dynamic recrystallization occurred at 600℃,resulting in a significant decrease in yield and tensile strength.Nevertheless,the UFG ferritic steels had an advantage in tensile strength(UTS)and elongation-to-failure(εf)at 600℃,especially at strain rate of 0.0017 s^(-1),with high UTSof 510 MPa and excellent low temperature(<0.42 Tm)superplasticity(εf=110%).These mechanical properties are significantly superior compared to similar type of steels at identical temperature.A mechanistic understanding of mechanical behavior of UFG ferritic steels is presented by combining the effect of strain rate,temperature,and nano-size carbides.
基金financially supported by the National Natu-ral Science Foundation of Chin a(Grant Nos.52101135,52101151,and 52171162)the Hong Kong Research Grant Coun-cil,University Grants Committee(RGC)with CityU grants Nos 21205621 and15227121+2 种基金Wealso thankthefinancialsupport from the Shenzhen Science and Technology Program(Grant No.RCBS20210609103202012)PKL very much appreciates the sup-port from(1)the National Science Foundation(Nos.DMR-1611180,1809640,and 2226508)(2)the US Army Research Office(Nos.W911NF-13-1-0438 and W911NF-19-2-0049).
文摘The precipitate morphologies,coarsening kinetics,elemental partitioning behaviors,grain structures,and tensile properties were explored in detail for L1_(2)-strengthened Ni_(39.9)Co_(20)Fe_(15)Cr_(15)Al_(6)Ti_(4-x)Nb_(x)B_(0.1)(x=0 at.%,2 at.%,and 4 at.%)high-entropy alloys(HEAs).By substituting Ti with Nb,the spheroidal-to-cuboidal precipitate morphological transition,increase in the coarsening kinetics,and phase decomposition upon aging at 800°C occurred.The excessive addition of Nb brings about the grain boundary precipitation of an Nb-rich phase along with the phase decomposition from the L1_(2)to lamellar-structured D019 phase upon the long-term aging duration.By partially substituting Ti with Nb,the chemically complex and thermally stable L12 phase with a composition of(Ni_(58.8)Co_(9.8)Fe_(2.7))(Al_(12.7)Ti_(5.8)Nb_(7.5)Cr_(2.3))ensures the stable phase structure and clean grain boundaries,which guarantees the superb high-temperature mechanical properties(791±7 MPa for yielding and 1013±11 MPa for failure)at 700℃.Stacking faults(SFs)were observed to prevail during the plastic deformation,offering a high work-hardening capability at 700°C.An anomalous rise in the yield strength at 800℃was found,which could be ascribed to the multi-layered super-partial dislocations with a cross-slip configuration within the L1_(2)particles.
基金financially supported by the National Key Research and Development Program of China(2016YFB0700300)the financial support from National Natural Science Foundation of China(No.52001271)+2 种基金the supports from the National Science Foundation(DMR-1611180 and 1809640)the US Army Research Office(W911NF-13-1-0438 and W911NF-19-20049)the Swiss National Science Foundation for support of this work by project"Harnessing atomicscale randomness:design and optimization of mechanical performance in High Entropy Alloys"(Project 200021_118198/1)。
文摘To accelerate the exploration,screening,and discovery of structural high-entropy alloys with targeted properties,the newly developed High-Throughput Hot-Isostatic-Pressing based Micro-Synthesis Approach(HT-HIP-MSA)is employed to efficiently synthesize and characterize 85 combinatorial alloys in a 13-principal element alloying space.These Co Cr Fe Ni-based high entropy alloys span 1 quaternary,9 quinary,and 36 senary alloy systems,and their composition-structure-property relationships are characterized and analyzed experimentally and computationally.From the single-phase FCC CoCrFeNi alloy base,with Mn,Cu,Ti,Nb,Ta,Mo,W,Al,and Si as principal element alloying additions,we find(1)the extended Mn solubility in the single-phase FCC CoCrFeNi-Mn_(x) alloys,(2)the destabilizing behavior for most of the quinary and senary alloys,and(3)the distinctive solid-solution-strengthening effects in the alloys.In combining the computational methods,the HT-HIP-MSA can be systematic and economic to explore and refine the compositions,structures,and properties of structural high-entropy alloys.
基金the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.51621004)the National Natural Science Foundation of China(Nos.12072109,51871092,and 11772122)。
文摘High entropy alloys(HEAs)attract remarkable attention due to the excellent mechanical performance.However,the origins of their high strength and toughness compared with those of the traditional alloys are still hardly revealed.Here,using a microstructure-based constitutive model and molecular dynamics(MD)simulation,we investigate the unique mechanical behavior and microstructure evolution of FeCoCrNiCu HEAs during the indentation.Due to the interaction between the dislocation and solution,the high dislocation density in FeCoCrNiCu leads to strong work hardening.Plentiful slip systems are stimulated,leading to the good plasticity of FeCoCrNiCu.The plastic deformation of FeCoCrNiCu is basically affected by the motion of dislocation loops.The prismatic dislocation loops inside FeCoCrNiCu are formed by the dislocations with the Burgers vectors of a/6[112]and a/6[112],which interact with each other,and then emit along the<111>slip direction.In addition,the mechanical properties of FeCoCrNiCu HEA can be predicted by constructing the microstructure-based constitutive model,which is identified according to the evolution of the dislocation density and the stress-strain curve.Strong dislocation strengthening and remarkable lattice distortion strengthening occur in the deformation process of FeCoCrNiCu,and improve the strength.Therefore,the origins of high strength and high toughness in FeCoCrNiCu HEAs come from lattice distortion strengthening and the more activable slip systems compared with Cu.These results accelerate the discovery of HEAs with excellent mechanical properties,and provide a valuable reference for the industrial application of HEAs.
基金Project supported by the National Natural Science Foundation of China(Nos.51871092 and 11772122)the Foundation for Innovative Research Groups of the National Natural Science Foundation of China(No.51621004)。
文摘Grain boundaries(GBs)can serve as effective sinks for radiation-induced defects,thus notably influencing the service performance of materials.However,the effect of GB structures on the zero-dimensional defects induced by irradiation has not been fully elucidated.Here,the evolution of cascade collision in the single-crystal(SC),bicrystalline(BC),and twinned crystalline(TC)copper is studied by atomic simulations during irradiation.The spatial distributions of vacancies and interstitials are closely related to the GB at a certain primary knock-on atom(PKA)energy.Compared with the TC,the BC displays a more obvious segregation of the interstitial atoms near GB,due to the characteristic of the greater interstitial binding energy.The evolution of Frenkel pairs is more sensitive to the change of the GB position in the BC.A more prominent defect annihilation rate is caused by the effect of the GB than that of the twin boundary(TB).The marked secondary emission phenomenon has been observed in the BC,which promotes the formation of an inverted pagoda-like defect distribution.There are similar sub-conical defect distributions and microstructures induced by cascade collision in the TC and the SC.It has been found that the influence range of the GB is wider in the BC.Meanwhile,the average flow stress of the irradiated copper is quantitatively calculated by establishing a physical strengthening model.The contribution of vacancy to the average flow stress in the irradiated BC and TC is obvious than that in the SC,due to the formation of many vacancies.This study provides a theoretical basis for further understanding and customization of the metal-based equipment with good radiation resistance.
文摘By means of rapid heating cyclic heat treatment, the microstructure of a TiAl-based alloy was refined. The colony size and lamellar spacing were measured to be 50 μm and 0.12 μm, respectively. The compression mechanical properties were determined at room temperature and the best comprehensive mechanical properties can reach σ0.2 of 745.1 MPa, σp of 1 672.2 MPa and δ of 19.40%. The improvement of mechanical properties is caused by the microstructural refinement and the phase interface nucleation contributes a lot to the refinement of microstructure.
基金X.F.and P.K.L.very much appreciate the support of the U.S.Army Research Office Project(W911NF-13-1-0438 and W911NF-19-2-0049)with the program managersDrs M.P.Bakas,S.N.Mathaudhu,and D.M.Stepp,as well as the support from the Bunch Fellowship.XF and PKL also would like to acknowledge funding from the State of Tennessee and Tennessee Higher Education Commission(THEC)through their support of the Center for Materials Processing(CMP).P.K.L.,furthermore,thanks the support from the National Science Foundation(DMR-1611180 and 1809640)with the program directors+1 种基金Drs J.Yang,G.Shiflet,and D.Farkas.B.S.very much appreciates the support from the National Science Foundation(IIP-1447395 and IIP-1632408)with the program directorsDr G.Larsen and R.Mehta,from the U.S.Air Force(FA864921P0754),with J.Evans as the program manager,and from the U.S.Navy(N6833521C0420),with Drs D.Shifler and J.Wolk as the program managers.M.C.G.acknowledges the support of the US Department of Energy’s Fossil Energy Crosscutting Technology Research Program.The authors also want to thank Dr.G.Tewksbury for bringing to their attention suspicious recordings of the US from the literature,which have prompted the data curation effort.
文摘This paper presents a bilinear log model,for predicting temperature-dependent ultimate strength of high-entropy alloys(HEAs)based on 21 HEA compositions.We consider the break temperature,Tbreak,introduced in the model,an important parameter for design of materials with attractive high-temperature properties,one warranting inclusion in alloy specifications.For reliable operation,the operating temperature of alloys may need to stay below Tbreak.We introduce a technique of global optimization,one enabling concurrent optimization of model parameters over low-temperature and high-temperature regimes.Furthermore,we suggest a general framework for joint optimization of alloy properties,capable of accounting for physics-based dependencies,and show how a special case can be formulated to address the identification of HEAs offering attractive ultimate strength.We advocate for the selection of an optimization technique suitable for the problem at hand and the data available,and for properly accounting for the underlying sources of variations.
