Eutectic high entropy alloys(EHEAs)have high temperature stability,good mechanical properties,and are promising for tribological applications at high temperatures.To study the high temperature lubrication behavior,Fe_...Eutectic high entropy alloys(EHEAs)have high temperature stability,good mechanical properties,and are promising for tribological applications at high temperatures.To study the high temperature lubrication behavior,Fe_(22)Co_(26)Cr_(20)Ni_(22)Ta_(10)−(BaF_(2)/CaF_(2))x(x=3−20,wt.%)composites were prepared by spark plasma sintering(SPS),with BaF_(2)/CaF_(2) eutectic powder used as solid lubricant.The lubrication behavior and mechanical properties were studied at both room and high temperatures.With the increase of the content of BaF_(2)/CaF_(2) eutectic powder,the friction coefficients and the wear rates of the composites at 600 and 800℃ decrease significantly.The composites with eutectic powder content of 15 and 20 wt.%have the best lubricating performance at 600℃,with low friction coefficient and wear rates,mainly due to the good mechanical properties of EHEA matrix,the lubrication effect of BaF_(2)/CaF_(2) phase and the oxides formed on the worn surface.展开更多
To study the effects of La on the microstructure and mechanical properties of refractory high entropy alloys,NbMoTiVSi0.2 alloys with different La contents were prepared.Phase constitution,microstructure evolution,com...To study the effects of La on the microstructure and mechanical properties of refractory high entropy alloys,NbMoTiVSi0.2 alloys with different La contents were prepared.Phase constitution,microstructure evolution,compressive properties and related mechanisms were systematically studied.Results show that the alloys with La addition are composed of BCC solid solution,eutectic structure,MSi2 disilicide phase and La-containing precipitates.Eutectic structure and most of La precipitates are formed at the grain boundaries.Disilicide phase is formed in the grains.La can change the grain morphologies from dendritic structure to near-equiaxed structure,and the average grain size decreases from 180 to 20μm with the increase of La content from 0 to 0.5 at.%.Compressive testing shows that the ultimate strength and the yield strength increase with the increase of La content,which is resulted from the grain boundary strengthening.However,they cannot be greatly improved because of the formation of MSi2 disilicide phase with low strength.The ductility decreases with the increase of La content,which is due to the La precipitates and brittle MSi2 disilicide phase.展开更多
FeNiCrCoSi_(x) and FeNiCrCoTi_(x)(x=0,0.3,0.6,and 0.9 wt.%)high entropy alloys(HEAs)were prepared via the powder metallurgy technique.A homogenous distribution of the elements in all alloys due to the formation of a s...FeNiCrCoSi_(x) and FeNiCrCoTi_(x)(x=0,0.3,0.6,and 0.9 wt.%)high entropy alloys(HEAs)were prepared via the powder metallurgy technique.A homogenous distribution of the elements in all alloys due to the formation of a solid solution phase is observed.The density and hardness of the prepared HEAs are improved by Si and Ti additions,compared to FeNiCrCo HEA.The wear rate of the prepared alloys was studied at different loads and the results indicate that the alloys that contain 0.3 wt.%Si and 0.9 wt.%Ti have the lowest wear rates.X-ray diffraction,SEM,and EDX were used to understand the phases,grain sizes,and microstructures in different investigated HEAs.The effects of Si and Ti content on the corrosion behavior and surface morphologies of sintered FeNiCrCoSi_(x) and FeNiCrCoTi_(x) HEAs were studied by immersion in H_(2)SO_(4),HNO_(3),and HCl solutions.Uniform corrosion and localized pitting are observed in different sizes in the corrosive media used.Because of the smaller pit size and the reduced pit density,the FeNiCrCoSi_(0.3) HEA has an excellent microstructure.展开更多
A novel AlCoCrFeNi2.1 eutectic high entropy alloy(EHEA)composite doped with SiC particles was designed and fabricated by laser powder bed fusion(LPBF).Its microstructure characteristic,tensile properties,and metallurg...A novel AlCoCrFeNi2.1 eutectic high entropy alloy(EHEA)composite doped with SiC particles was designed and fabricated by laser powder bed fusion(LPBF).Its microstructure characteristic,tensile properties,and metallurgical defects,with an emphasis on cracking behavior,have been investigated.The results showed that the addition of SiC particles into the AlCoCrFeNi_(2.1)matrix enabled the development of a{100}texture and highly elongated columnar grains,which were the main contributors to mechanical behavior anisotropy.The ultimate tensile strength of 1466±26 MPa and elongation of 9%±3%achieved in the as-deposited EHEA composite surpassed those of advanced metal alloys subjected to additive manufacturing processes.Unfortunately,severe horizontal and longitudinal cracks,as well as a few micro-cracks were observed in the as-deposited bulk samples.Micro-cracks were verified to be associated with the aggregation of carbon and oxide particles.They formed in the final stage of solidification owing to insufficient liquid feeding ability and solidification contraction.The formation of macroscopic cracking was induced by the tensile stress accumulations at sample edges,and the stress concentration areas where microcracks and pores were located were the predominant propagation location.This work provides guidelines for defect control in SiC-reinforced EHEA,assisting in the high-performance design and integrated manufacturing of EHEA composite components.展开更多
Heterostructured eutectic high-entropy alloys(EHEAs)have attracted significant attention owing to their novel properties,such as balanced combinations of strength and fracture toughness.However,the toughening/strength...Heterostructured eutectic high-entropy alloys(EHEAs)have attracted significant attention owing to their novel properties,such as balanced combinations of strength and fracture toughness.However,the toughening/strengthening mechanisms of these EHEAs have not been thoroughly investigated.In this study,we developed a series of dual-phase Al_((18–2x))Co_(30)Cr_((11+x))Fe_((11+x))Ni_(3)0(x=-1,0,1)eutectic and neareutectic HEAs containing face-centered cubic(FCC)and body-centered cubic(BCC)phases.Despite the high amount of BCC,which is referred to as the brittle phase,newly developed EHEAs exhibited superior fracture toughness.Interestingly,we discovered that a fully eutectic HEA exhibited further improvements in both yield stress and fracture toughness,outperforming our off-eutectic and other previously reported HEAs.By combining experiments and theoretical models,we demonstrated that the synergistic increase in both strength and toughness in our fully eutectic HEA was derived from the high hetero-deformationinduced(HDI)strengthening/toughening associated with a high misorientation angle at the grain/phase boundaries.展开更多
AlCoCrFeNi_(2.1-x)NbC(x=0,2.5,7.5,and 10 wt%,denoted as NbC0,NbC2.5,NbC7.5,and NbC10)high-entropy alloy(HEA)matrix composites were fabricated by mechanical alloying(MA)and spark plasma sintering(SPS)methods.The effect...AlCoCrFeNi_(2.1-x)NbC(x=0,2.5,7.5,and 10 wt%,denoted as NbC0,NbC2.5,NbC7.5,and NbC10)high-entropy alloy(HEA)matrix composites were fabricated by mechanical alloying(MA)and spark plasma sintering(SPS)methods.The effect of NbC content on the microstructures,Vickers hardness,and wear properties of AlCoCrFeNi_(2.1) eutectic high entropy alloy(EHEA)was systematically investigated.The results indicate that the AlCoCrFeNi_(2.1) alloy consisted of FCC,B2,Al_(2)O_(3),and Cr_(7)C_(3) phases,while the AlCoCrFeNi_(2.1-x)NbC(x>0)alloys consisted of FCC,NbC,Al_(2)O_(3),and Cr_(7)C_(3) phases.The AlCoCrFeNi_(2.1-x)NbC alloys exhibit excellent Vickers hardness with 679 HV,664 HV,677 HV,and 695 HV,respectively.In addition,with the addition of NbC,the average friction coefficient and wear rate of the AlCoCrFeNi_(2.1)-xNbC alloys decrease from 0.59 to 0.42 and from 1.5.10–5 mm^(3) N^(−1) m^(−1) to 2.4.10–6 mm^(3) N^(−1) m^(−1),respectively.Wherein,NbC10 alloy shows the smallest average friction coefficient of 0.42 and lowest wear rate of 2.4.10–6 mm^(3) N^(−1) m^(−1),indicating that the NbC10 alloy displays the best wear resistance.And the wear mechanism of the NbC10 alloy was oxidation wear accompanied by slight adhesive wear.展开更多
Eutectic high entropy alloy(EHEA)possesses promising prospects for industrial application due to its controllable and near-equilibrium dual-phase structure.Due to the advantages of high material utiliza-tion,efficient...Eutectic high entropy alloy(EHEA)possesses promising prospects for industrial application due to its controllable and near-equilibrium dual-phase structure.Due to the advantages of high material utiliza-tion,efficient production,and design freedom,the laser powder bed fusion(LPBF)technique provides a new path to prepare EHEA components with complex structure and excellent performance.In this study,near fully dense AlCoCrFeNi_(2.1) samples were obtained by adjusting the process parameters of LPBF.Con-sidering the balling phenomenon and powder splashing during the LPBF process,laser remelting was selected as an optimized scanning strategy to further improve the forming quality of AlCoCrFeNi21.The microstructure of remelted AlCoCrFeNi_(2.1) sample exhibited regular eutectic lamellae consisting of nano-scale face-centered-cubic(FCC)and B2 phases,in which the FCC phase accounted for a higher proportion.By investigating the tensile behavior and deformation mechanism,it was revealed that the ultrafine eu-tectic lamellae could induce a strong dual-phase synergistic strengthening,thereby significantly improv-ing the strength of the sample.Compared with the vacuum induction melted(VIM)sample,the remelted sample showed a 54%increase in ultimate tensile strength(UTS-1518 MPa)and a 130%increase in yield strength(YS-1235 MPa)with reasonable plasticity.This study indicates that by combining the design and manufacturing freedom of LPBF with the EHEA,it is expected to fabricate high-property 3D EHEA parts,expanding the application field of EHEA.展开更多
High-strength metallic foams have a wide range of applications in engineering as lightweight structural and energy-absorbing materials.However,it is challenging to obtain metallic foam with both good energy absorption...High-strength metallic foams have a wide range of applications in engineering as lightweight structural and energy-absorbing materials.However,it is challenging to obtain metallic foam with both good energy absorption performance and high strength.Here,we developed a novel metal matrix syntactic foam fabri-cated with AlCoCrFeNi_(2.1) eutectic high entropy alloy and alumina cenospheres that exhibits a remarkable combination of high strength and energy absorption performance under both quasi-static and dynamic compression.The porous structure of syntactic foam fully exploits the properties of the AlCoCrFeNi_(2.1) alloy matrix with a unique FCC/B2 dual-phase eutectic microstructure and thus yields exceptional per-formance.We discovered that this dual-phase microstructure not only provides high strength but also allows the pores to collapse in a progressive and diffusive way,which enables the formation of a high and smooth energy absorption platform.It is found that the heterogeneity between the two phases in the matrix can provide back stress strengthening,and it also induces multiple micro shear bands and microcracks as additional energy dissipation modes as the deformation proceeds.This unique mechanism ensures the strength of microstructures and makes them fracture promptly,which causes the balance of strengthening and softening on the macro scale.This work opens the avenue for developing advanced high-strength lightweight structural and energy-absorbing materials.展开更多
In order to improve mechanical properties of refractory high entropy alloys,silicide was introduced and NbMoTiVSi_(x)(x=0,0.1,0.2,0.3,and 0.4,molar ratio) refractory high entropy alloys are prepared by vacuum arc melt...In order to improve mechanical properties of refractory high entropy alloys,silicide was introduced and NbMoTiVSi_(x)(x=0,0.1,0.2,0.3,and 0.4,molar ratio) refractory high entropy alloys are prepared by vacuum arc melting.Phase composition,micro structure evolution and mechanical properties were systematically studied.Results show that the silicide phase is formed in the alloys with addition of silicon,and the volume fraction of silicide increases from 0 to 8.3 % with increasing of silicon.Microstructure observation shows that the morphology of dendrite changes from columnar to near equiaxed,eutectic structure is formed at grain boundaries and composed of secondary BCC phase and silicide phase.The average length of the primary and second dendrites decreases with the increasing of silicon.Whereas,the ratio of eutectic structure increases from 0 to 19.8 % with the increment of silicon.The refinement of microstructure is caused by heterogeneous nucleation from the silicide.Compressive tests show that the yield and ultimate strength of the alloys increases from 1141.5 MPa to 2093.1 MPa and from 1700.1 MPa to 2374.7 MPa with increasing silicon content.The fracture strain decreases from 24.7 %-11.0 %.Fracture mechanism is changed from ductile fracture to ductile and brittle mixed fracture.The improvement of the strength is caused by grain bounda ry strengthening,which includes more boundaries around primary BCC phase and eutectic structure in grain boundary,both of them is resulted from the formation of silicide.展开更多
Eutectic and near-eutectic high entropy alloys （HEAs） have recently attracted a great deal of interest because of their promising properties, such as an excellent castability and unique combination of good ductility...Eutectic and near-eutectic high entropy alloys （HEAs） have recently attracted a great deal of interest because of their promising properties, such as an excellent castability and unique combination of good ductility and high strength. However, in the absence of a phase diagram, it remains a non-trivial task to find a eutectic or near-eutectic composition for a HEA system, which usually demands a tremendous amount of efforts if a trial-and-error approach is followed. In this paper, we briefly review the thermodynamics that governs the entectic solidification in regular binary and ternary alloys, and proceed to the discussion for the design of eutectic HEAs. Based on the data reported, we then propose an improved strategy which may enable an efficient search for the eutectic or near eutectic HEA compositions.展开更多
The emergence of eutectic high-entropy alloys(EHEAs)offers new insights into the design of next generation structural alloys,which is due to their stable dual-phase microstructure and outstanding mechanical properties...The emergence of eutectic high-entropy alloys(EHEAs)offers new insights into the design of next generation structural alloys,which is due to their stable dual-phase microstructure and outstanding mechanical properties from room to elevated temperatures.In this work,a series of(CoFe2 NiV0.5Mo0.2)100-xNbx(0≤x≤12)EHEAs were designed and prepared via vacuum arc-melting.Typical eutectic microstructure composing lamellar face-centered cubic solid solution phase and C14 Laves phase appears in the as-cast EHEA when x=9.The microstructure turns to hypoeutectic or hypereutectic when x is below or beyond that critical value accordingly.The volume fraction of the hard Laves phase is proportional to the Nb addition,leading to the strength increment yet at the expense of ductility at room temperature.In particular,the EHEA having4 at%Nb shows a compressive strength of 2.1 GPa with an elongation to fracture of 45%,while EHEAs containing 9 and10 at%Nb exhibit ultrahigh yield strengths of over 1.4 GPa.The effect of Nb addition on the corrosion resistance of this Crfree EHEA system was also studied.The EHEA containing 9 at%Nb has the best anti-corrosion performance in the 3.5 wt%NaCl solution at 298±1 K,indicating a good combination of mechanical and corrosion properties.展开更多
In the present study,a series of AlCoCrxFeNi2.1(x=0,0.25,0.5,0.75,1.0)eutectic high entropy alloys(EHEAs)have been designed and prepared.And the effect of Cr content on the microstructures and mechanical properties of...In the present study,a series of AlCoCrxFeNi2.1(x=0,0.25,0.5,0.75,1.0)eutectic high entropy alloys(EHEAs)have been designed and prepared.And the effect of Cr content on the microstructures and mechanical properties of the AlCoCrxFeNi2.1 alloys was systematically investigated.The results indicate that the AlCoCrxFeNi2.1(x>0)alloys exhibit almost complete lamellar eutectic microstructures with a mixture structure of FCC and B2 phases.And the AlCoFeNi2.1 alloy without Cr element exhibited a hypoeutectic microstructure with a primary B2 phase.In addition,the eutectic microstructures for AlCoCrxFeNi2.1 eutectic alloys do not change significantly.The room temperature compressive tests results show that with an increase in Cr content(from x=0 to x=1.0),the yield strength will first decrease,and thereafter increase.The trend is the opposite with the fracture strength and plastic strain.They show an increase trend at first,and then decrease.The AlCoCr0.5 FeNi2.1(Cr0.5)alloy shows the best comprehensive mechanical properties.The tensile yield strength,fracture strength,and elongation are 536.5 MPa,1062 MPa,and 13.8%,respectively.Furthermore,the Cr0.5 alloy also displays a high strength with a yield strength of 362 MPa at 700℃.In summary,by changing the Cr content,AlCoCrxFeNi2.1 eutectic high entropy alloys with excellent comprehensive mechanical properties were obtained and prepared.展开更多
基金The authors acknowledge the financial support from the National Natural Science Foundation of China(51671217).
文摘Eutectic high entropy alloys(EHEAs)have high temperature stability,good mechanical properties,and are promising for tribological applications at high temperatures.To study the high temperature lubrication behavior,Fe_(22)Co_(26)Cr_(20)Ni_(22)Ta_(10)−(BaF_(2)/CaF_(2))x(x=3−20,wt.%)composites were prepared by spark plasma sintering(SPS),with BaF_(2)/CaF_(2) eutectic powder used as solid lubricant.The lubrication behavior and mechanical properties were studied at both room and high temperatures.With the increase of the content of BaF_(2)/CaF_(2) eutectic powder,the friction coefficients and the wear rates of the composites at 600 and 800℃ decrease significantly.The composites with eutectic powder content of 15 and 20 wt.%have the best lubricating performance at 600℃,with low friction coefficient and wear rates,mainly due to the good mechanical properties of EHEA matrix,the lubrication effect of BaF_(2)/CaF_(2) phase and the oxides formed on the worn surface.
基金The authors are grateful for the financial supports from the National Natural Science Foundation of China(51825401 and 52001114)the State Key Laboratory of Materials Processing and Die&Mould Technology(P2020-023)the Guangdong Introducing Innovative and Entrepreneurial Teams,China(2016ZT06G025).
文摘To study the effects of La on the microstructure and mechanical properties of refractory high entropy alloys,NbMoTiVSi0.2 alloys with different La contents were prepared.Phase constitution,microstructure evolution,compressive properties and related mechanisms were systematically studied.Results show that the alloys with La addition are composed of BCC solid solution,eutectic structure,MSi2 disilicide phase and La-containing precipitates.Eutectic structure and most of La precipitates are formed at the grain boundaries.Disilicide phase is formed in the grains.La can change the grain morphologies from dendritic structure to near-equiaxed structure,and the average grain size decreases from 180 to 20μm with the increase of La content from 0 to 0.5 at.%.Compressive testing shows that the ultimate strength and the yield strength increase with the increase of La content,which is resulted from the grain boundary strengthening.However,they cannot be greatly improved because of the formation of MSi2 disilicide phase with low strength.The ductility decreases with the increase of La content,which is due to the La precipitates and brittle MSi2 disilicide phase.
文摘FeNiCrCoSi_(x) and FeNiCrCoTi_(x)(x=0,0.3,0.6,and 0.9 wt.%)high entropy alloys(HEAs)were prepared via the powder metallurgy technique.A homogenous distribution of the elements in all alloys due to the formation of a solid solution phase is observed.The density and hardness of the prepared HEAs are improved by Si and Ti additions,compared to FeNiCrCo HEA.The wear rate of the prepared alloys was studied at different loads and the results indicate that the alloys that contain 0.3 wt.%Si and 0.9 wt.%Ti have the lowest wear rates.X-ray diffraction,SEM,and EDX were used to understand the phases,grain sizes,and microstructures in different investigated HEAs.The effects of Si and Ti content on the corrosion behavior and surface morphologies of sintered FeNiCrCoSi_(x) and FeNiCrCoTi_(x) HEAs were studied by immersion in H_(2)SO_(4),HNO_(3),and HCl solutions.Uniform corrosion and localized pitting are observed in different sizes in the corrosive media used.Because of the smaller pit size and the reduced pit density,the FeNiCrCoSi_(0.3) HEA has an excellent microstructure.
基金the Guangdong Basic and Applied Basic Research Foundation(grant No.2021B1515120028)National Natural Science Foundation of China(grant Nos.52130204,52174376,51822405,and 52202070)+5 种基金Science and Technology Innovation Team Plan of Shann Xi Province(grant No.2021TD-17)Youth Innovation Team of Shaanxi UniversitiesThousands Person Plan of Jiangxi Province(grant No.JXSQ2020102131)Xi’an Science and Technology Program(grant No.21ZCZZHXJS-QCY6-0005)Fundamental Research Funds for the Central Universities(grant Nos.D5000210902 and D5000220057)Innovation Foundation for Doctor Dissertation of Northwestern Polytechnical University(grant No.CX2022033).
文摘A novel AlCoCrFeNi2.1 eutectic high entropy alloy(EHEA)composite doped with SiC particles was designed and fabricated by laser powder bed fusion(LPBF).Its microstructure characteristic,tensile properties,and metallurgical defects,with an emphasis on cracking behavior,have been investigated.The results showed that the addition of SiC particles into the AlCoCrFeNi_(2.1)matrix enabled the development of a{100}texture and highly elongated columnar grains,which were the main contributors to mechanical behavior anisotropy.The ultimate tensile strength of 1466±26 MPa and elongation of 9%±3%achieved in the as-deposited EHEA composite surpassed those of advanced metal alloys subjected to additive manufacturing processes.Unfortunately,severe horizontal and longitudinal cracks,as well as a few micro-cracks were observed in the as-deposited bulk samples.Micro-cracks were verified to be associated with the aggregation of carbon and oxide particles.They formed in the final stage of solidification owing to insufficient liquid feeding ability and solidification contraction.The formation of macroscopic cracking was induced by the tensile stress accumulations at sample edges,and the stress concentration areas where microcracks and pores were located were the predominant propagation location.This work provides guidelines for defect control in SiC-reinforced EHEA,assisting in the high-performance design and integrated manufacturing of EHEA composite components.
基金supported by the National Research Foundation of Korea(No.NRF-2021R1A6A3A0108674211)the Fundamental Research Program of the Korean Institute of Materials Science(No.PNK8730)by Research Grant Council(RGC),Hong Kong Government,through General Research Fund(Nos.CityU11213118,CityU11200719 and CityU11209317).
文摘Heterostructured eutectic high-entropy alloys(EHEAs)have attracted significant attention owing to their novel properties,such as balanced combinations of strength and fracture toughness.However,the toughening/strengthening mechanisms of these EHEAs have not been thoroughly investigated.In this study,we developed a series of dual-phase Al_((18–2x))Co_(30)Cr_((11+x))Fe_((11+x))Ni_(3)0(x=-1,0,1)eutectic and neareutectic HEAs containing face-centered cubic(FCC)and body-centered cubic(BCC)phases.Despite the high amount of BCC,which is referred to as the brittle phase,newly developed EHEAs exhibited superior fracture toughness.Interestingly,we discovered that a fully eutectic HEA exhibited further improvements in both yield stress and fracture toughness,outperforming our off-eutectic and other previously reported HEAs.By combining experiments and theoretical models,we demonstrated that the synergistic increase in both strength and toughness in our fully eutectic HEA was derived from the high hetero-deformationinduced(HDI)strengthening/toughening associated with a high misorientation angle at the grain/phase boundaries.
基金This work was supported by the Natural Science Foundation of Shandong Province(No.ZR2020QE019)the National Natural Science Foundation of China(No.51901116)the China Postdoctoral Science Fund(No.2021M692724).
文摘AlCoCrFeNi_(2.1-x)NbC(x=0,2.5,7.5,and 10 wt%,denoted as NbC0,NbC2.5,NbC7.5,and NbC10)high-entropy alloy(HEA)matrix composites were fabricated by mechanical alloying(MA)and spark plasma sintering(SPS)methods.The effect of NbC content on the microstructures,Vickers hardness,and wear properties of AlCoCrFeNi_(2.1) eutectic high entropy alloy(EHEA)was systematically investigated.The results indicate that the AlCoCrFeNi_(2.1) alloy consisted of FCC,B2,Al_(2)O_(3),and Cr_(7)C_(3) phases,while the AlCoCrFeNi_(2.1-x)NbC(x>0)alloys consisted of FCC,NbC,Al_(2)O_(3),and Cr_(7)C_(3) phases.The AlCoCrFeNi_(2.1-x)NbC alloys exhibit excellent Vickers hardness with 679 HV,664 HV,677 HV,and 695 HV,respectively.In addition,with the addition of NbC,the average friction coefficient and wear rate of the AlCoCrFeNi_(2.1)-xNbC alloys decrease from 0.59 to 0.42 and from 1.5.10–5 mm^(3) N^(−1) m^(−1) to 2.4.10–6 mm^(3) N^(−1) m^(−1),respectively.Wherein,NbC10 alloy shows the smallest average friction coefficient of 0.42 and lowest wear rate of 2.4.10–6 mm^(3) N^(−1) m^(−1),indicating that the NbC10 alloy displays the best wear resistance.And the wear mechanism of the NbC10 alloy was oxidation wear accompanied by slight adhesive wear.
基金supported by the National Natural Science Foundation of China (Grant No.U21A2043)the Youth Innovation Promotion Association,CAS (No.2022191)the Bintech-IMR R&D Program (No.GYY-JSBU-2022-010).
文摘Eutectic high entropy alloy(EHEA)possesses promising prospects for industrial application due to its controllable and near-equilibrium dual-phase structure.Due to the advantages of high material utiliza-tion,efficient production,and design freedom,the laser powder bed fusion(LPBF)technique provides a new path to prepare EHEA components with complex structure and excellent performance.In this study,near fully dense AlCoCrFeNi_(2.1) samples were obtained by adjusting the process parameters of LPBF.Con-sidering the balling phenomenon and powder splashing during the LPBF process,laser remelting was selected as an optimized scanning strategy to further improve the forming quality of AlCoCrFeNi21.The microstructure of remelted AlCoCrFeNi_(2.1) sample exhibited regular eutectic lamellae consisting of nano-scale face-centered-cubic(FCC)and B2 phases,in which the FCC phase accounted for a higher proportion.By investigating the tensile behavior and deformation mechanism,it was revealed that the ultrafine eu-tectic lamellae could induce a strong dual-phase synergistic strengthening,thereby significantly improv-ing the strength of the sample.Compared with the vacuum induction melted(VIM)sample,the remelted sample showed a 54%increase in ultimate tensile strength(UTS-1518 MPa)and a 130%increase in yield strength(YS-1235 MPa)with reasonable plasticity.This study indicates that by combining the design and manufacturing freedom of LPBF with the EHEA,it is expected to fabricate high-property 3D EHEA parts,expanding the application field of EHEA.
基金supported by the NSFC Basic Science Cen-ter Program for“MultiscaleProblems inNonlinear Mechanics”(No.11988102)the NSFC(Nos.11790292,11972346 and 11672316)+2 种基金Ye Qisun Science Foundation of NSFC(No.U2141204)the Key Research Program of the Chinese Academy of Sciences(No.ZDRW-CN-2021-2-3)the Strategic Priority Research Program of the Chinese Academy of Sciences(Nos.XDB22040302 and XDB22040303).
文摘High-strength metallic foams have a wide range of applications in engineering as lightweight structural and energy-absorbing materials.However,it is challenging to obtain metallic foam with both good energy absorption performance and high strength.Here,we developed a novel metal matrix syntactic foam fabri-cated with AlCoCrFeNi_(2.1) eutectic high entropy alloy and alumina cenospheres that exhibits a remarkable combination of high strength and energy absorption performance under both quasi-static and dynamic compression.The porous structure of syntactic foam fully exploits the properties of the AlCoCrFeNi_(2.1) alloy matrix with a unique FCC/B2 dual-phase eutectic microstructure and thus yields exceptional per-formance.We discovered that this dual-phase microstructure not only provides high strength but also allows the pores to collapse in a progressive and diffusive way,which enables the formation of a high and smooth energy absorption platform.It is found that the heterogeneity between the two phases in the matrix can provide back stress strengthening,and it also induces multiple micro shear bands and microcracks as additional energy dissipation modes as the deformation proceeds.This unique mechanism ensures the strength of microstructures and makes them fracture promptly,which causes the balance of strengthening and softening on the macro scale.This work opens the avenue for developing advanced high-strength lightweight structural and energy-absorbing materials.
基金supported by National Natural Science Foundation of China(Grant No.51825401,51971121)Fundamental Research Funds of Henan University of Technology(Grant No.2018QNJH25)+1 种基金Scientific Research Fund of State Key Laboratory of Materials Processing and Die&Mould Technology(Grant No.P2020-023)the Program for Guangdong Introducing Innovative and Entrepreneurial Teams(NO:2016ZT06G025)。
文摘In order to improve mechanical properties of refractory high entropy alloys,silicide was introduced and NbMoTiVSi_(x)(x=0,0.1,0.2,0.3,and 0.4,molar ratio) refractory high entropy alloys are prepared by vacuum arc melting.Phase composition,micro structure evolution and mechanical properties were systematically studied.Results show that the silicide phase is formed in the alloys with addition of silicon,and the volume fraction of silicide increases from 0 to 8.3 % with increasing of silicon.Microstructure observation shows that the morphology of dendrite changes from columnar to near equiaxed,eutectic structure is formed at grain boundaries and composed of secondary BCC phase and silicide phase.The average length of the primary and second dendrites decreases with the increasing of silicon.Whereas,the ratio of eutectic structure increases from 0 to 19.8 % with the increment of silicon.The refinement of microstructure is caused by heterogeneous nucleation from the silicide.Compressive tests show that the yield and ultimate strength of the alloys increases from 1141.5 MPa to 2093.1 MPa and from 1700.1 MPa to 2374.7 MPa with increasing silicon content.The fracture strain decreases from 24.7 %-11.0 %.Fracture mechanism is changed from ductile fracture to ductile and brittle mixed fracture.The improvement of the strength is caused by grain bounda ry strengthening,which includes more boundaries around primary BCC phase and eutectic structure in grain boundary,both of them is resulted from the formation of silicide.
基金supported by the City University of Hong Kong through the UGC Block Grant with the Project(Grant No.9610366)
文摘Eutectic and near-eutectic high entropy alloys （HEAs） have recently attracted a great deal of interest because of their promising properties, such as an excellent castability and unique combination of good ductility and high strength. However, in the absence of a phase diagram, it remains a non-trivial task to find a eutectic or near-eutectic composition for a HEA system, which usually demands a tremendous amount of efforts if a trial-and-error approach is followed. In this paper, we briefly review the thermodynamics that governs the entectic solidification in regular binary and ternary alloys, and proceed to the discussion for the design of eutectic HEAs. Based on the data reported, we then propose an improved strategy which may enable an efficient search for the eutectic or near eutectic HEA compositions.
基金financially supported by the National MCF Energy R&D Program (No. 2018YFE0312400)National Key Research and Development Program of China (No. 2019YFA0209901)+2 种基金National Natural Science Foundation of China (Nos. 51822402 and 51671044)Fundamental Research Funds for the Central Universities (No. DUT16ZD206)LiaoNing Revitalization Talents Program (No. XLYC1807047)。
文摘The emergence of eutectic high-entropy alloys(EHEAs)offers new insights into the design of next generation structural alloys,which is due to their stable dual-phase microstructure and outstanding mechanical properties from room to elevated temperatures.In this work,a series of(CoFe2 NiV0.5Mo0.2)100-xNbx(0≤x≤12)EHEAs were designed and prepared via vacuum arc-melting.Typical eutectic microstructure composing lamellar face-centered cubic solid solution phase and C14 Laves phase appears in the as-cast EHEA when x=9.The microstructure turns to hypoeutectic or hypereutectic when x is below or beyond that critical value accordingly.The volume fraction of the hard Laves phase is proportional to the Nb addition,leading to the strength increment yet at the expense of ductility at room temperature.In particular,the EHEA having4 at%Nb shows a compressive strength of 2.1 GPa with an elongation to fracture of 45%,while EHEAs containing 9 and10 at%Nb exhibit ultrahigh yield strengths of over 1.4 GPa.The effect of Nb addition on the corrosion resistance of this Crfree EHEA system was also studied.The EHEA containing 9 at%Nb has the best anti-corrosion performance in the 3.5 wt%NaCl solution at 298±1 K,indicating a good combination of mechanical and corrosion properties.
基金supported by the National Natural Science Foundation of China(No.51901116)the Natural Science Foundation of Shandong Province(No.ZR2020QE019)the China Postdoctoral Science Fund(No.2021M692724)。
文摘In the present study,a series of AlCoCrxFeNi2.1(x=0,0.25,0.5,0.75,1.0)eutectic high entropy alloys(EHEAs)have been designed and prepared.And the effect of Cr content on the microstructures and mechanical properties of the AlCoCrxFeNi2.1 alloys was systematically investigated.The results indicate that the AlCoCrxFeNi2.1(x>0)alloys exhibit almost complete lamellar eutectic microstructures with a mixture structure of FCC and B2 phases.And the AlCoFeNi2.1 alloy without Cr element exhibited a hypoeutectic microstructure with a primary B2 phase.In addition,the eutectic microstructures for AlCoCrxFeNi2.1 eutectic alloys do not change significantly.The room temperature compressive tests results show that with an increase in Cr content(from x=0 to x=1.0),the yield strength will first decrease,and thereafter increase.The trend is the opposite with the fracture strength and plastic strain.They show an increase trend at first,and then decrease.The AlCoCr0.5 FeNi2.1(Cr0.5)alloy shows the best comprehensive mechanical properties.The tensile yield strength,fracture strength,and elongation are 536.5 MPa,1062 MPa,and 13.8%,respectively.Furthermore,the Cr0.5 alloy also displays a high strength with a yield strength of 362 MPa at 700℃.In summary,by changing the Cr content,AlCoCrxFeNi2.1 eutectic high entropy alloys with excellent comprehensive mechanical properties were obtained and prepared.
