A high-pressure die casting(HPDC)Mg-5Gd-1.5Sm-0.7Al alloy was newly developed and exhibits outstanding strength-ductility synergy,with the yield strength and the tensile elongation to fracture being approximately 200 ...A high-pressure die casting(HPDC)Mg-5Gd-1.5Sm-0.7Al alloy was newly developed and exhibits outstanding strength-ductility synergy,with the yield strength and the tensile elongation to fracture being approximately 200 MPa and 8.5%,respectively.This alloy has two types of a-Mg grains:coarse a_(1)-Mg((46±18)μm)and fine a_(2)-Mg((9.2±2.3)μm)grains,and various Al-GS(GS=Gd and Sm)particles located at grain boundaries while clear solute-atom segregation near grain boundaries with limited or free intermetallic particles.Characterizations using Cs-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)indicate the crystal structures of Al-GS phases.After aging,denseβ'precipitates and chain-shapedβ''-like structures precipitated near grain boundaries while a high density of ultrafineβ''-(Mg,Al)3Sm precipitates and Al-GS clusters formed in grain center.Relatively fine grains,Al-GS primary particles,solute-atom segregation near grain boundaries,and/or multiple precipitates contribute to the high strength of the studied alloy,while the multi-scale a-Mg grains,variety of intermetallic particles but discontinuous skeleton,and the multi-typed precipitated lead to its satisfactory ductility.展开更多
In this study,the mechanical behavior of crystal group of hexagonal close-packed(hcp;αphase)and body-centered cubic(bcc;βphase)during tensile loading was investigated to elucidate the mechanism from elastic to plast...In this study,the mechanical behavior of crystal group of hexagonal close-packed(hcp;αphase)and body-centered cubic(bcc;βphase)during tensile loading was investigated to elucidate the mechanism from elastic to plastic deformation transition of the rolled LZ91 Mg alloy using transmission-X-ray diffraction(transmission-XRD)measurement,transmission electron microscopy(TEM),scanning transmission electron microscopy(STEM),energy dispersive X-ray spectroscopy(EDS).The approximate proof stress of the LZ91 Mg alloy sample was found that the lattice strain retained the expanded state from 0.6%nominal strain,and the transmission-XRD measurement characterized the crystalline behavior during the transition by the integrated intensity of crystal group hcp(100).The lattice strain of bcc(110)decreased from the 0.6%nominal strain due to dislocation activity,which occurred nearβ/βgrain boundary.In addition,we performed the analyses of electron energy loss spectroscopy(EELS)modes,the Li-K peak disappeared from the segregated Li regions of 10–60 nm nearβ/βgrain boundary at the nominal strain of 0.8%.Understanding this mechanical behavior during the elastic to plastic deformation transition by transmission-XRD is crucial for the development of Mg-Li alloys.展开更多
Mg-6Zn-1Y(at.%)ribbons with strengthening precipitates of multi-type nanoquasicrystals were prepared by melt-spinning followed by aging treatments.Microstructural evolution of the rapidly solidified ribbons during iso...Mg-6Zn-1Y(at.%)ribbons with strengthening precipitates of multi-type nanoquasicrystals were prepared by melt-spinning followed by aging treatments.Microstructural evolution of the rapidly solidified ribbons during isothermal aging was comprehensively studied using various electron microscopy techniques.Two new kinds of decagonal quasicrystals were formed in aged ribbons,in addition to precipitation of nanometer icosahedral quasicrystals.Atomic-resolution observations reveal that both decagonal quasicrystals can be modeled by quasiperiodic tiling with decagonal clusters of 2.5 nm in diameter,but overlap of neighboring clusters in both decagonal quasicrystals is different from the Gummelt model observed in other quasicrystals.A shell composed of complex Laves Mg-Zn domains was formed surrounding each decagonal quasicrystal precipitate upon prolonged aging.In addition,all kinds of nanoprecipitates exhibit excellent structure and size stability at 573 K.Our findings may have implications for not only fundamental studies about quasicrystals,but also microstructural manipulation of high-performance Mg alloys.展开更多
The precipitation of the lamellar-shaped M23C6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 ℃ has been investigated. Such a precipitation is not commonly observed in...The precipitation of the lamellar-shaped M23C6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 ℃ has been investigated. Such a precipitation is not commonly observed in cobalt-base superalloys. It is found that M23C6 particles nucleate preferentially at stacking faults （SFs） in the dendritic matrix and grow along the SFs to develop a lamellar character. Additionally, a Cr depletion zone is observed in the vicinity of the lamellar M23C6 carbide, which strongly supports the presence of Suzuki segregation.展开更多
Twinning and precipitation play important roles in deformation and strengthening of magnesium alloys.In this work,interfacial precipitation in{1012}twin boundaries(TBs)of a cold-stamped Mg-12Gd-1.2Zn-0.4Zr alloy was i...Twinning and precipitation play important roles in deformation and strengthening of magnesium alloys.In this work,interfacial precipitation in{1012}twin boundaries(TBs)of a cold-stamped Mg-12Gd-1.2Zn-0.4Zr alloy was investigated using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy.Extended periodic segregation of Gd+Zn atoms in the~86.2°{1012}TBs with basal-prismatic facets and in the symmetric tilting TBs(obviously>86.2°)frequently occurred,resulted in the formation of new interfacial phases,namelyβ_(TB)’having a monoclinic structure in the TBs with two segregation layers andβ_(TB) having a tetragonal structure in the TBs with three or more segregation layers.The formation ofβ_(TB) clearly accelerates peak-aging and improves the alloy’s strength.展开更多
A mass of GaN nanowires has been successfully synthesized on Si（111） substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950℃. X-ray diffraction, scanning electron microscopy, high resolution t...A mass of GaN nanowires has been successfully synthesized on Si（111） substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950℃. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscope and Fourier transformed infrared spectra are used to characterize the samples. The results demonstrate that the nanowires are of single-crystal GaN with a hexagonal wurtzite structure and possess relatively smooth surfaces. The growth mechanism of GaN nanowires is also discussed.展开更多
High purity Fe3O4 /helical carbon nanofiber composites were obtained on a large scale by the catalytic pyrolysis of ferrocene in the presence of tin powder at 500°C over 12 h. The sizes of Fe 3 O 4 nanoparticles ...High purity Fe3O4 /helical carbon nanofiber composites were obtained on a large scale by the catalytic pyrolysis of ferrocene in the presence of tin powder at 500°C over 12 h. The sizes of Fe 3 O 4 nanoparticles are 35–65 nm in size, and the diameters of the helical carbon nanofibers range from 40–70 nm. The shapes and compositions of the nanocomposites are simply controlled by adjusting the reaction temperatures. On the basis of the obtained experimental results the formation of the helical Fe3O4/carbon nanofiber composites was investigated and discussed. The magnetic hysteresis loop of the products shows ferromagnetic behavior with saturation magnetization (M s ), remanent magnetization (M r ) and coercivity (H c ) values of ca. 29.8 emu/g, 9.6 emu/g and 306.6 Oe, respectively.展开更多
基金Project supported by the Scientific and Technological Developing Scheme of Jilin Province(20220101239JC,YDZJ202301ZYTS538)the Chinese Academy of Sciences Youth Innovation Promotion Association(2023234)。
文摘A high-pressure die casting(HPDC)Mg-5Gd-1.5Sm-0.7Al alloy was newly developed and exhibits outstanding strength-ductility synergy,with the yield strength and the tensile elongation to fracture being approximately 200 MPa and 8.5%,respectively.This alloy has two types of a-Mg grains:coarse a_(1)-Mg((46±18)μm)and fine a_(2)-Mg((9.2±2.3)μm)grains,and various Al-GS(GS=Gd and Sm)particles located at grain boundaries while clear solute-atom segregation near grain boundaries with limited or free intermetallic particles.Characterizations using Cs-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)indicate the crystal structures of Al-GS phases.After aging,denseβ'precipitates and chain-shapedβ''-like structures precipitated near grain boundaries while a high density of ultrafineβ''-(Mg,Al)3Sm precipitates and Al-GS clusters formed in grain center.Relatively fine grains,Al-GS primary particles,solute-atom segregation near grain boundaries,and/or multiple precipitates contribute to the high strength of the studied alloy,while the multi-scale a-Mg grains,variety of intermetallic particles but discontinuous skeleton,and the multi-typed precipitated lead to its satisfactory ductility.
基金supported by The SUHARA MEMORIAL FOUNDATION [grant number SF-2023-A1]JSPS KAKENHI [grant numbers JP16K05961 and JP19K04065]supported by Hokkaido University's microstructural characterization platform under a program of “Nanotechnology Platform,” within the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan
文摘In this study,the mechanical behavior of crystal group of hexagonal close-packed(hcp;αphase)and body-centered cubic(bcc;βphase)during tensile loading was investigated to elucidate the mechanism from elastic to plastic deformation transition of the rolled LZ91 Mg alloy using transmission-X-ray diffraction(transmission-XRD)measurement,transmission electron microscopy(TEM),scanning transmission electron microscopy(STEM),energy dispersive X-ray spectroscopy(EDS).The approximate proof stress of the LZ91 Mg alloy sample was found that the lattice strain retained the expanded state from 0.6%nominal strain,and the transmission-XRD measurement characterized the crystalline behavior during the transition by the integrated intensity of crystal group hcp(100).The lattice strain of bcc(110)decreased from the 0.6%nominal strain due to dislocation activity,which occurred nearβ/βgrain boundary.In addition,we performed the analyses of electron energy loss spectroscopy(EELS)modes,the Li-K peak disappeared from the segregated Li regions of 10–60 nm nearβ/βgrain boundary at the nominal strain of 0.8%.Understanding this mechanical behavior during the elastic to plastic deformation transition by transmission-XRD is crucial for the development of Mg-Li alloys.
基金supported by the National Natural Science Foundation of China (grant number: 51771202, 51971225, 52001225)Key Research of Frontier Science, Chinese Academy of Science (grant number: QYZDY-SSW-JSC207)+1 种基金Ji Hua Laboratory (X210141TL210)Guangdong Province (2021B0301030003)
文摘Mg-6Zn-1Y(at.%)ribbons with strengthening precipitates of multi-type nanoquasicrystals were prepared by melt-spinning followed by aging treatments.Microstructural evolution of the rapidly solidified ribbons during isothermal aging was comprehensively studied using various electron microscopy techniques.Two new kinds of decagonal quasicrystals were formed in aged ribbons,in addition to precipitation of nanometer icosahedral quasicrystals.Atomic-resolution observations reveal that both decagonal quasicrystals can be modeled by quasiperiodic tiling with decagonal clusters of 2.5 nm in diameter,but overlap of neighboring clusters in both decagonal quasicrystals is different from the Gummelt model observed in other quasicrystals.A shell composed of complex Laves Mg-Zn domains was formed surrounding each decagonal quasicrystal precipitate upon prolonged aging.In addition,all kinds of nanoprecipitates exhibit excellent structure and size stability at 573 K.Our findings may have implications for not only fundamental studies about quasicrystals,but also microstructural manipulation of high-performance Mg alloys.
基金supported by the National Natural Science Foundation of China (Nos. 51331005, 51601192, 51671188 and 11332010)the High Technology Research and Development Program of China (No. 2014AA041701)
文摘The precipitation of the lamellar-shaped M23C6 carbide within the dendritic matrix of a cobalt-base superalloy during thermal exposure at 1000 ℃ has been investigated. Such a precipitation is not commonly observed in cobalt-base superalloys. It is found that M23C6 particles nucleate preferentially at stacking faults （SFs） in the dendritic matrix and grow along the SFs to develop a lamellar character. Additionally, a Cr depletion zone is observed in the vicinity of the lamellar M23C6 carbide, which strongly supports the presence of Suzuki segregation.
基金financially supported by the Scientific and Technological Developing Scheme of Jilin Province under grants No.YDZJ202102CXJD012,20200801048GH,20200602021ZPthe Capital Construction Founds of Jilin Province with Innovation Capacity Building under grants No.2021C038-1。
文摘Twinning and precipitation play important roles in deformation and strengthening of magnesium alloys.In this work,interfacial precipitation in{1012}twin boundaries(TBs)of a cold-stamped Mg-12Gd-1.2Zn-0.4Zr alloy was investigated using atomic-resolution high-angle annular dark-field scanning transmission electron microscopy.Extended periodic segregation of Gd+Zn atoms in the~86.2°{1012}TBs with basal-prismatic facets and in the symmetric tilting TBs(obviously>86.2°)frequently occurred,resulted in the formation of new interfacial phases,namelyβ_(TB)’having a monoclinic structure in the TBs with two segregation layers andβ_(TB) having a tetragonal structure in the TBs with three or more segregation layers.The formation ofβ_(TB) clearly accelerates peak-aging and improves the alloy’s strength.
基金Project supported by the National Natural Science Foundation of China (Grant Nos 90201025 and 90301002)
文摘A mass of GaN nanowires has been successfully synthesized on Si（111） substrates by magnetron sputtering through ammoniating Ga2O3/Co films at 950℃. X-ray diffraction, scanning electron microscopy, high resolution transmission electron microscope and Fourier transformed infrared spectra are used to characterize the samples. The results demonstrate that the nanowires are of single-crystal GaN with a hexagonal wurtzite structure and possess relatively smooth surfaces. The growth mechanism of GaN nanowires is also discussed.
基金supported by the National Basic Research Program of China (2011CB935901)the Start Fund for Advanced Professional of Jiangsu University of Science and Technology (35060810)
文摘High purity Fe3O4 /helical carbon nanofiber composites were obtained on a large scale by the catalytic pyrolysis of ferrocene in the presence of tin powder at 500°C over 12 h. The sizes of Fe 3 O 4 nanoparticles are 35–65 nm in size, and the diameters of the helical carbon nanofibers range from 40–70 nm. The shapes and compositions of the nanocomposites are simply controlled by adjusting the reaction temperatures. On the basis of the obtained experimental results the formation of the helical Fe3O4/carbon nanofiber composites was investigated and discussed. The magnetic hysteresis loop of the products shows ferromagnetic behavior with saturation magnetization (M s ), remanent magnetization (M r ) and coercivity (H c ) values of ca. 29.8 emu/g, 9.6 emu/g and 306.6 Oe, respectively.
