Critical engineering applications,such as landing gears and armor protection,require structural materials withstanding high strength and significant plastic deformation.Nanoprecipitate-strengthened high-entropy alloys...Critical engineering applications,such as landing gears and armor protection,require structural materials withstanding high strength and significant plastic deformation.Nanoprecipitate-strengthened high-entropy alloys(HEAs)are considered as promising candidates for structural applications due to their enhanced strength and exceptional work-hardening capability.Herein,we report a FeCoNiAlTi-type HEA that achieves ultrahigh gigapascal yield strength from quasi-static to dynamic loading conditions and superb resistance to adiabatic shear failure.This is accomplished by introducing high-density coherent L1_(2) nanoprecipitates.Multiscale characterization and molecular dynamics simulation demonstrate that the L1_(2) nanoprecipitates exhibit multiple functions during impact,not only as the dislocation barrier and the dislocation transmission medium,but also as energyabsorbing islands that disperse the stress spikes through order-to-disorder transition,which result in extraordinary impact resistance.These findings shed light on the development of novel impact-resistant metallic materials.展开更多
Deformation behavior of a FeCrNi medium entropy alloy(MEA)prepared by powder metallurgy(P/M)method was investigated over a wide range of strain rates.The FeCrNi MEA exhibits high strain-hardening ability,which can be ...Deformation behavior of a FeCrNi medium entropy alloy(MEA)prepared by powder metallurgy(P/M)method was investigated over a wide range of strain rates.The FeCrNi MEA exhibits high strain-hardening ability,which can be attributed to the multiple deformation mechanisms,including dislocation slip,deformation induced stacking fault and mechanical twinning.The shear localization behavior of the FeCrNi MEA was also analyzed by dynamically loading hat-shaped specimens,and the distinct adiabatic shear band cannot be observed until the shear strain reaches~14.5.The microstructures within and outside the shear band exhibit different characteristics:the grains near the shear band are severely elongated and significantly refined by dislocation slip and twinning;inside the shear band,the initial coarse grains completely disappear,and transform into recrystallized ultrafine equiaxed grains by the classical rotational dynamic recrystallization mechanism.Moreover,microvoids preferentially nucleate in the central areas of the shear band where the temperature is very high and the shear stress is highly concentrated.These microvoids will coalesce into microcracks with the increase of strain,which eventually leads to the fracture of the shear band.展开更多
The microstructural modification for cellular structures can achieve the improvement of dynamic me-chanical properties of a selective laser melted FeCoNiCrMo_(0.2)high-entropy alloy(SLM-FeCoNiCrMo_(0.2)HEA)and can exp...The microstructural modification for cellular structures can achieve the improvement of dynamic me-chanical properties of a selective laser melted FeCoNiCrMo_(0.2)high-entropy alloy(SLM-FeCoNiCrMo_(0.2)HEA)and can expand its promising applications in the field of high-velocity deformation.In this work,FeCoNiCrMo_(0.2)HEAs with cellular structures in different sizes were produced by selective laser melt-ing(SLM)with different process parameters.The dynamic mechanical properties and microstructure of the SLM-FeCoNiCrMo_(0.2)HEA were studied.The dynamic mechanical properties of the SLM-FeCoNiCrMo_(0.2)HEA increased with decrease of average size of cellular structures,and the values of them were sensitive to strain rates.The energy absorption,compressive strength and yield strength of the SLM-FeCoNiCrMo_(0.2)HEAs reached 315.6 MJ/m^(3),2.2 GPa and 775.6 MPa,respectively at a strain rate of 2,420 s^(−1),under the process parameters of laser power and scanning speed of 330 W and 800 mm/s,respectively,where the corresponding average size of cellular structures in the HEAs was 483.6 nm.The value of strain-hardening rate of the SLM-FeCoNiCrMo_(0.2)HEA was about 5.1 GPa at a strain level of 0.1,which was much higher than that of the powder-metallurgy FeCoNiCrMo_(0.2)HEA.The cellular structure was formed inside the molten pool with segregation of Mo on the boundary.Deformation localization appeared in the cellular structures,forming several deformation bands after high strain-rate deformation.The elemental segre-gation strengthening and dislocation strengthening are considered to be the main strengthening mecha-nisms in SLM-FeCoNiCrMo_(0.2)HEA.展开更多
There are nanotwins in the shear band formed in a moment(about 10^(−5)s)in some NiCrFe-based medium-entropy alloys(MEAs),and these shear bands can be recognized as a special kind of materials due to their high strengt...There are nanotwins in the shear band formed in a moment(about 10^(−5)s)in some NiCrFe-based medium-entropy alloys(MEAs),and these shear bands can be recognized as a special kind of materials due to their high strength and good plasticity.In this study,the single shear band of the NiCrFe MEA was prepared at 77 K.A series of characterizations were carried out to analyze the microstructures in the shear band.The strength of the shear band was investigated by the split Hopkinson pressure bar and in-situ compression.The micropillar in the shear band containing nanotwins exhibits excellent strengthplasticity synergy.The compressive yield strength of the shear band measured by in-situ compression is 175%higher than that of the matrix,reaching 1405 MPa,with the fracture strain exceeding 0.5.The strengthening mechanism of the shear band was revealed by the combination of the experimental results and molecular dynamics simulation.The synergistic effect of multiple strengthening mechanisms enhances the strength of the NiCrFe MEA containing nanotwins,in which the grain boundary strengthening of the ultrafine equiaxed grains and the dynamic Hall–Petch effect of the nanotwins dominate.In addition,the good plasticity of the shear band is ascribed to the stress concentration reduction of the twin boundaries of nanotwins and the activation of multiple slip systems due to the randomly oriented nanotwins.These findings provide theoretical guidance for the design of nanotwinned MEAs to realize excellent strength-plasticity synergy for structural materials.展开更多
An in situ autogenous particle-reinforced Ti-2.5Zr-2Al-1(Si,C)titanium alloy is prepared by vacuum induction melting.The wide range of an effective strain between 0.2 and 1.2 and the corresponding microstructure are o...An in situ autogenous particle-reinforced Ti-2.5Zr-2Al-1(Si,C)titanium alloy is prepared by vacuum induction melting.The wide range of an effective strain between 0.2 and 1.2 and the corresponding microstructure are obtained by the double-cone high-throughput compression test and finite element simulation.The deformation mechanism diagram with strains of 0.2-1.2 and strain rates of 0.7-1.5 s^(-1)at 900℃ is constructed.When the strain rate is 1.3 s^(-1),dynamic recovery occurs in the small strain range(<0.377),dynamic recrystallization(DRX)occurs in the medium strain range(0.377-1.182),and deformation instability occurs in the large strain range(>1.182),resulting in the deformation bands.High-angle annular dark field and high-resolution transmission electron microscopy are used to determine the existence of bimodal particle distribution,namely micron-scale TiC particles and nano-scale Ti5Si3 and(Zr,Si)particles.The average radius of the(Zr,Si)nanoparticles measured by small angle neutron scattering is 19.3 nm,and the volume fraction is 0.35%.DRX grains with an average size of 0.49μm are obtained at 900°C,strain rate of 1.3 s^(-1),and strain of about 0.6.Micron-scale particles stimulated DRX nucleation,while nanoscale particles hindered the growth of new grains,resulting in grain refinement.展开更多
To the Editor:Post-vitrectomy vitreous hemorrhage(PVH)is one of the most common complications of vitrectomy.[1-3]Unfortunately,there have been no studies on how to adopt a conservative approach to PVH.We describe a me...To the Editor:Post-vitrectomy vitreous hemorrhage(PVH)is one of the most common complications of vitrectomy.[1-3]Unfortunately,there have been no studies on how to adopt a conservative approach to PVH.We describe a method that eliminates the need to go to the operating room and mechanically accelerates the removal of PVH.展开更多
基金the National Natural Science Foundation of China(Grant No.52020105013 and 52401223)Natural Science Foundation of Hunan Province(Grant No.2022JJ20001)+1 种基金Science and Technology Foundation Strengthening Program(Grant No.6142902210104)T.Y.is grateful for the financial support from the Research Grants Council of the Hong Kong Special Administrative Region,China(Grant No.C1020-21G).
文摘Critical engineering applications,such as landing gears and armor protection,require structural materials withstanding high strength and significant plastic deformation.Nanoprecipitate-strengthened high-entropy alloys(HEAs)are considered as promising candidates for structural applications due to their enhanced strength and exceptional work-hardening capability.Herein,we report a FeCoNiAlTi-type HEA that achieves ultrahigh gigapascal yield strength from quasi-static to dynamic loading conditions and superb resistance to adiabatic shear failure.This is accomplished by introducing high-density coherent L1_(2) nanoprecipitates.Multiscale characterization and molecular dynamics simulation demonstrate that the L1_(2) nanoprecipitates exhibit multiple functions during impact,not only as the dislocation barrier and the dislocation transmission medium,but also as energyabsorbing islands that disperse the stress spikes through order-to-disorder transition,which result in extraordinary impact resistance.These findings shed light on the development of novel impact-resistant metallic materials.
基金supported by the National Natural Science Foundation of China[Grant numbers 52020105013,51771232]。
文摘Deformation behavior of a FeCrNi medium entropy alloy(MEA)prepared by powder metallurgy(P/M)method was investigated over a wide range of strain rates.The FeCrNi MEA exhibits high strain-hardening ability,which can be attributed to the multiple deformation mechanisms,including dislocation slip,deformation induced stacking fault and mechanical twinning.The shear localization behavior of the FeCrNi MEA was also analyzed by dynamically loading hat-shaped specimens,and the distinct adiabatic shear band cannot be observed until the shear strain reaches~14.5.The microstructures within and outside the shear band exhibit different characteristics:the grains near the shear band are severely elongated and significantly refined by dislocation slip and twinning;inside the shear band,the initial coarse grains completely disappear,and transform into recrystallized ultrafine equiaxed grains by the classical rotational dynamic recrystallization mechanism.Moreover,microvoids preferentially nucleate in the central areas of the shear band where the temperature is very high and the shear stress is highly concentrated.These microvoids will coalesce into microcracks with the increase of strain,which eventually leads to the fracture of the shear band.
基金The present work was financially supported by the National Natural Science of China(No.52020105013)by the State Key Laboratory of Powder Metallurgy(No.62102172).
文摘The microstructural modification for cellular structures can achieve the improvement of dynamic me-chanical properties of a selective laser melted FeCoNiCrMo_(0.2)high-entropy alloy(SLM-FeCoNiCrMo_(0.2)HEA)and can expand its promising applications in the field of high-velocity deformation.In this work,FeCoNiCrMo_(0.2)HEAs with cellular structures in different sizes were produced by selective laser melt-ing(SLM)with different process parameters.The dynamic mechanical properties and microstructure of the SLM-FeCoNiCrMo_(0.2)HEA were studied.The dynamic mechanical properties of the SLM-FeCoNiCrMo_(0.2)HEA increased with decrease of average size of cellular structures,and the values of them were sensitive to strain rates.The energy absorption,compressive strength and yield strength of the SLM-FeCoNiCrMo_(0.2)HEAs reached 315.6 MJ/m^(3),2.2 GPa and 775.6 MPa,respectively at a strain rate of 2,420 s^(−1),under the process parameters of laser power and scanning speed of 330 W and 800 mm/s,respectively,where the corresponding average size of cellular structures in the HEAs was 483.6 nm.The value of strain-hardening rate of the SLM-FeCoNiCrMo_(0.2)HEA was about 5.1 GPa at a strain level of 0.1,which was much higher than that of the powder-metallurgy FeCoNiCrMo_(0.2)HEA.The cellular structure was formed inside the molten pool with segregation of Mo on the boundary.Deformation localization appeared in the cellular structures,forming several deformation bands after high strain-rate deformation.The elemental segre-gation strengthening and dislocation strengthening are considered to be the main strengthening mecha-nisms in SLM-FeCoNiCrMo_(0.2)HEA.
基金supported by the National Natural Science Foundation of China(Grant Nos.51771231,52020105013)The authors express their sincerest gratitude to Professor Marc A.Meyers at the University of California,San Diego for his advice and helpsThe authors also express their sincere thanks to Professor Yong Liu and Bin Liu at the University of Central South University for their advice and helps.
文摘There are nanotwins in the shear band formed in a moment(about 10^(−5)s)in some NiCrFe-based medium-entropy alloys(MEAs),and these shear bands can be recognized as a special kind of materials due to their high strength and good plasticity.In this study,the single shear band of the NiCrFe MEA was prepared at 77 K.A series of characterizations were carried out to analyze the microstructures in the shear band.The strength of the shear band was investigated by the split Hopkinson pressure bar and in-situ compression.The micropillar in the shear band containing nanotwins exhibits excellent strengthplasticity synergy.The compressive yield strength of the shear band measured by in-situ compression is 175%higher than that of the matrix,reaching 1405 MPa,with the fracture strain exceeding 0.5.The strengthening mechanism of the shear band was revealed by the combination of the experimental results and molecular dynamics simulation.The synergistic effect of multiple strengthening mechanisms enhances the strength of the NiCrFe MEA containing nanotwins,in which the grain boundary strengthening of the ultrafine equiaxed grains and the dynamic Hall–Petch effect of the nanotwins dominate.In addition,the good plasticity of the shear band is ascribed to the stress concentration reduction of the twin boundaries of nanotwins and the activation of multiple slip systems due to the randomly oriented nanotwins.These findings provide theoretical guidance for the design of nanotwinned MEAs to realize excellent strength-plasticity synergy for structural materials.
基金supported by the State Key Laboratory of Powder Metallurgy,China(grant no.2022)Innovation Province Construction Special Project of Hunan(grant no.2020GK4018)+2 种基金the National Natural Science of China(grant no.51771231 and 52020105013)Yubin Ke is grateful for the support from the National Natural Science Foundation of China(grant no.12275154)the Youth Innovation Promotion Association,CAS(no.2020010).
文摘An in situ autogenous particle-reinforced Ti-2.5Zr-2Al-1(Si,C)titanium alloy is prepared by vacuum induction melting.The wide range of an effective strain between 0.2 and 1.2 and the corresponding microstructure are obtained by the double-cone high-throughput compression test and finite element simulation.The deformation mechanism diagram with strains of 0.2-1.2 and strain rates of 0.7-1.5 s^(-1)at 900℃ is constructed.When the strain rate is 1.3 s^(-1),dynamic recovery occurs in the small strain range(<0.377),dynamic recrystallization(DRX)occurs in the medium strain range(0.377-1.182),and deformation instability occurs in the large strain range(>1.182),resulting in the deformation bands.High-angle annular dark field and high-resolution transmission electron microscopy are used to determine the existence of bimodal particle distribution,namely micron-scale TiC particles and nano-scale Ti5Si3 and(Zr,Si)particles.The average radius of the(Zr,Si)nanoparticles measured by small angle neutron scattering is 19.3 nm,and the volume fraction is 0.35%.DRX grains with an average size of 0.49μm are obtained at 900°C,strain rate of 1.3 s^(-1),and strain of about 0.6.Micron-scale particles stimulated DRX nucleation,while nanoscale particles hindered the growth of new grains,resulting in grain refinement.
文摘To the Editor:Post-vitrectomy vitreous hemorrhage(PVH)is one of the most common complications of vitrectomy.[1-3]Unfortunately,there have been no studies on how to adopt a conservative approach to PVH.We describe a method that eliminates the need to go to the operating room and mechanically accelerates the removal of PVH.
