In the present study,we selected solutes to be added to the Cr Co Ni medium-entropy alloy(MEA)based on the mismatch of self-diffusion activation energy(SDQ)between the alloying elements and constituent elements of the...In the present study,we selected solutes to be added to the Cr Co Ni medium-entropy alloy(MEA)based on the mismatch of self-diffusion activation energy(SDQ)between the alloying elements and constituent elements of the matrix,and then investigated their grain growth behavior and mechanical properties.Mo and Al were selected as the solutes for investigation primarily because they have higher and lower SDQ,respectively,than those of the matrix elements;a secondary factor was their higher and lower shear modulus.Their concentrations were fixed at 3 at.%each because previous work had shown these compositions to be single-phase solid solutions with the face-centered cubic structure.Three alloys were produced by arc melting,casting,homogenizing,cold rolling and annealing at various temperatures and times to produce samples with different grain sizes.They were(a)the base alloy Cr Co Ni,(b)the base alloy plus 3 at.%Mo,and(c)the base alloy plus 3 at.%Al.The activation energies for grain growth of the Cr Co Ni,Cr Co Ni-3Mo and CrCo Ni-3Al MEAs were found to be^251,~368 and^219 k J/mol,respectively,consistent with the notion that elements with higher SDQ(in this study Mo)retard grain growth(likely by a solute-drag effect),whereas those with lower values(Al)accelerate grain growth.The roomtemperature tensile properties show that Mo increases the yield strength by^40%but Al addition has a smaller strengthening effect consistent with their relative shear moduli.The yield strength as a function of grain size for the three single-phase MEAs follows the classical Hall-Petch relationship with much higher slopes(>600 MPaμm-0.5)than traditional solid solutions.This work shows that the grain growth kinetics and solid solution strengthening of the Cr Co Ni MEA can be tuned by selecting solute elements that have appropriate diffusion and physical properties.展开更多
The Cr Fe Co Ni high-entropy alloy(HEA)exhibits excellent mechanical properties at lower temperatures due to its low stacking-fault energy,however,its medium-and high-temperature strengths are still insufficient.In co...The Cr Fe Co Ni high-entropy alloy(HEA)exhibits excellent mechanical properties at lower temperatures due to its low stacking-fault energy,however,its medium-and high-temperature strengths are still insufficient.In consideration of the potential diversified applications,more strengthening approaches except for the previously proposed L12 phase hardening deserve further exploration due to its rapid coarsening tendency at high temperatures.Here,we achieved significant high-temperature strengthening of the cast Cr Fe Co Ni HEA by in-situ precipitation of highly thermostable carbides.Alloys with 0.5 at.%and 1 at.%niobium and carbon were prepared by simple casting processes,i.e.drop cast,solute solution and aging.A highly thermostable microstructure was formed,which comprises very coarse grains accompanied with extensive thermostable carbide precipitates embedded,including submicrometer coherent Nb C particles in grain interiors and intergranular coherent M_(23)C_(6)carbides.This high thermostability of microstructure,which is beneficial for the high-temperature loading,is ascribed to the synergy of lacking growth driving force and Zenner pinning effect by the carbides.Tensile properties tested at 673,873 and1073 K show that the yield strength and ultimate tensile strength are significantly increased by Nb/C doping,along with the elongation escalation at higher temperatures.The strengthening is mainly due to the precipitation hardening of carbide particles.展开更多
Grain boundaries(GBs)are often known as intergranular cracking sources in alloys at high temperatures,resulting in limited high-temperature strength and ductility.Here,we propose a GB-dual-carbide(de-noted as GB-DC)st...Grain boundaries(GBs)are often known as intergranular cracking sources in alloys at high temperatures,resulting in limited high-temperature strength and ductility.Here,we propose a GB-dual-carbide(de-noted as GB-DC)strengthening strategy and have developed a high-performance(NiCoFeCr)99 Nb0.5 C0.5 high-entropy alloy(HEA)with exceptional strength-ductility synergy at 1073 K.Chain-like coherent M23 C6 carbides have been successfully introduced at GBs and remain a cube parallel crystallographic orientation with the face-centered cubic(FCC)matrix during deformation.Nano-scale NbC particles are distributed alternatively between M23 C6 carbides and inhibit their coarsening.Both strength and duc-tility of the GB-DC HEA increase dramatically at strain rates ranging from 10^(−4) to 10^(−2) s^(−1) at 1073 K,compared with those of the single-phase NiCoFeCr HEA.Specifically,yield strength of 142 MPa,ultimate tensile strength of 283 MPa,and elongation of 34%were obtained,which are twice that of the refer-ence NiCoFeCr HEA(82 MPa,172 MPa,and 18%,respectively).EBSD investigations demonstrated that chain-like carbides enhance the GB cohesion at high temperature,and TEM analysis revealed that dislo-cations can go through the coherent phase boundaries(CPBs)and activate dipoles inner M23 C6 carbides,which weakened the stress concentration in GBs.This substantially reduces the critical stress for dislo-cation generation and transmission to a stress level lower than that required for intergranular fracture.Theoretical estimation suggests that carbides result in a much higher activation energy(∼510 kJ/mol)for GB sliding and a rather low interface energy(∼101 mJ/m^(2))compared with the GB energy(1000 mJ/m^(2)),which rationalizes the enhanced GB cohesion by carbides.展开更多
Implantation is an essential issue in orthopedic surgery.Bulk metallic glasses(BMGs),as a kind of novel materials,attract lots of attentions in biological field owing to their comprehensive excellent properties.Here,w...Implantation is an essential issue in orthopedic surgery.Bulk metallic glasses(BMGs),as a kind of novel materials,attract lots of attentions in biological field owing to their comprehensive excellent properties.Here,we show that a Zr_(61)Ti_(2)Cu_(25)Al_(12)(at.%)BMG(Zr-based BMG)displays the best cytocompatibility,pronounced positive effects on cellular migration,and tube formation from in-vitro tests as compared to those of commercial-pure titanium and poly-ether-ether-ketone.The in-vivo micro-CT and histological evaluation demonstrate the Zr-based BMG can significantly promote a bone formation.Immunofluorescence tests and digital reconstructed radiographs manifest a stimulated effect on early blood vessel formation from the Zr-based BMG.Accordingly,the intimate connection and coupling effect between angiogenesis and osteogenesis must be effective during bone regeneration after implanting Zr-based BMG.Dynamic gait analysis in rats after implanting Zr-based BMG demonstrates a tendency to decrease the pain level during recovery,simultaneously,without abnormal ionic accumulation and inflammatory reactions.Considering suitable mechanical properties,we provide a realistic candidate of the Zr61Ti2Cu25Al12 BMG for biomedical applications.展开更多
基金the U.S.Department of Energy,Office of Science,Basic Energy Sciences,Materials Sciences and Engineering Division,E.P.Georgethe National Nature Science Foundation of China(No.51971099)+3 种基金the open fund of State Key Laboratory for Advanced Metals and Materials(No.2018-ZD03),X.W.Liuthe National Nature Science Foundation of China(No.51975425),L.C.Zengthe open fund of State Key Laboratory of Materials Processing and Die&Mould Technology(P2019-005),H.Duthe Research and Development Program of Jiangxi Academy of Sciences(No.2020-YZD-23),Q.Hu。
文摘In the present study,we selected solutes to be added to the Cr Co Ni medium-entropy alloy(MEA)based on the mismatch of self-diffusion activation energy(SDQ)between the alloying elements and constituent elements of the matrix,and then investigated their grain growth behavior and mechanical properties.Mo and Al were selected as the solutes for investigation primarily because they have higher and lower SDQ,respectively,than those of the matrix elements;a secondary factor was their higher and lower shear modulus.Their concentrations were fixed at 3 at.%each because previous work had shown these compositions to be single-phase solid solutions with the face-centered cubic structure.Three alloys were produced by arc melting,casting,homogenizing,cold rolling and annealing at various temperatures and times to produce samples with different grain sizes.They were(a)the base alloy Cr Co Ni,(b)the base alloy plus 3 at.%Mo,and(c)the base alloy plus 3 at.%Al.The activation energies for grain growth of the Cr Co Ni,Cr Co Ni-3Mo and CrCo Ni-3Al MEAs were found to be^251,~368 and^219 k J/mol,respectively,consistent with the notion that elements with higher SDQ(in this study Mo)retard grain growth(likely by a solute-drag effect),whereas those with lower values(Al)accelerate grain growth.The roomtemperature tensile properties show that Mo increases the yield strength by^40%but Al addition has a smaller strengthening effect consistent with their relative shear moduli.The yield strength as a function of grain size for the three single-phase MEAs follows the classical Hall-Petch relationship with much higher slopes(>600 MPaμm-0.5)than traditional solid solutions.This work shows that the grain growth kinetics and solid solution strengthening of the Cr Co Ni MEA can be tuned by selecting solute elements that have appropriate diffusion and physical properties.
基金financially supported by the National Nature Science Foundation of China(Nos.51971099 and 11805171)。
文摘The Cr Fe Co Ni high-entropy alloy(HEA)exhibits excellent mechanical properties at lower temperatures due to its low stacking-fault energy,however,its medium-and high-temperature strengths are still insufficient.In consideration of the potential diversified applications,more strengthening approaches except for the previously proposed L12 phase hardening deserve further exploration due to its rapid coarsening tendency at high temperatures.Here,we achieved significant high-temperature strengthening of the cast Cr Fe Co Ni HEA by in-situ precipitation of highly thermostable carbides.Alloys with 0.5 at.%and 1 at.%niobium and carbon were prepared by simple casting processes,i.e.drop cast,solute solution and aging.A highly thermostable microstructure was formed,which comprises very coarse grains accompanied with extensive thermostable carbide precipitates embedded,including submicrometer coherent Nb C particles in grain interiors and intergranular coherent M_(23)C_(6)carbides.This high thermostability of microstructure,which is beneficial for the high-temperature loading,is ascribed to the synergy of lacking growth driving force and Zenner pinning effect by the carbides.Tensile properties tested at 673,873 and1073 K show that the yield strength and ultimate tensile strength are significantly increased by Nb/C doping,along with the elongation escalation at higher temperatures.The strengthening is mainly due to the precipitation hardening of carbide particles.
基金sponsored by the fund of National Natural Sci-ence Foundation of China(Grant No.52371028 and 52271097)the State Key Laboratory of Solidification Processing in NPU(Grant No.SKLSP202401)the Fundamental Research Funds for the Central Universities,HUST(No.2023JYCXJJ016).
文摘Grain boundaries(GBs)are often known as intergranular cracking sources in alloys at high temperatures,resulting in limited high-temperature strength and ductility.Here,we propose a GB-dual-carbide(de-noted as GB-DC)strengthening strategy and have developed a high-performance(NiCoFeCr)99 Nb0.5 C0.5 high-entropy alloy(HEA)with exceptional strength-ductility synergy at 1073 K.Chain-like coherent M23 C6 carbides have been successfully introduced at GBs and remain a cube parallel crystallographic orientation with the face-centered cubic(FCC)matrix during deformation.Nano-scale NbC particles are distributed alternatively between M23 C6 carbides and inhibit their coarsening.Both strength and duc-tility of the GB-DC HEA increase dramatically at strain rates ranging from 10^(−4) to 10^(−2) s^(−1) at 1073 K,compared with those of the single-phase NiCoFeCr HEA.Specifically,yield strength of 142 MPa,ultimate tensile strength of 283 MPa,and elongation of 34%were obtained,which are twice that of the refer-ence NiCoFeCr HEA(82 MPa,172 MPa,and 18%,respectively).EBSD investigations demonstrated that chain-like carbides enhance the GB cohesion at high temperature,and TEM analysis revealed that dislo-cations can go through the coherent phase boundaries(CPBs)and activate dipoles inner M23 C6 carbides,which weakened the stress concentration in GBs.This substantially reduces the critical stress for dislo-cation generation and transmission to a stress level lower than that required for intergranular fracture.Theoretical estimation suggests that carbides result in a much higher activation energy(∼510 kJ/mol)for GB sliding and a rather low interface energy(∼101 mJ/m^(2))compared with the GB energy(1000 mJ/m^(2)),which rationalizes the enhanced GB cohesion by carbides.
基金The financial supports from the NSFC[Nos.51801027,51925103,51827801,81972121]the 111 project[No.D16002]are all appreciated.
文摘Implantation is an essential issue in orthopedic surgery.Bulk metallic glasses(BMGs),as a kind of novel materials,attract lots of attentions in biological field owing to their comprehensive excellent properties.Here,we show that a Zr_(61)Ti_(2)Cu_(25)Al_(12)(at.%)BMG(Zr-based BMG)displays the best cytocompatibility,pronounced positive effects on cellular migration,and tube formation from in-vitro tests as compared to those of commercial-pure titanium and poly-ether-ether-ketone.The in-vivo micro-CT and histological evaluation demonstrate the Zr-based BMG can significantly promote a bone formation.Immunofluorescence tests and digital reconstructed radiographs manifest a stimulated effect on early blood vessel formation from the Zr-based BMG.Accordingly,the intimate connection and coupling effect between angiogenesis and osteogenesis must be effective during bone regeneration after implanting Zr-based BMG.Dynamic gait analysis in rats after implanting Zr-based BMG demonstrates a tendency to decrease the pain level during recovery,simultaneously,without abnormal ionic accumulation and inflammatory reactions.Considering suitable mechanical properties,we provide a realistic candidate of the Zr61Ti2Cu25Al12 BMG for biomedical applications.
