The crystallography of phase transformation is an important issue for studying metallic alloys.Here,we demonstrate an abnormal orientation relation between face-centered cubic(fcc) and hexagonal closepacked(hcp) phase...The crystallography of phase transformation is an important issue for studying metallic alloys.Here,we demonstrate an abnormal orientation relation between face-centered cubic(fcc) and hexagonal closepacked(hcp) phases due to the intersection of two ε_(hcp)-martensite variants in a high manganese steel.The corresponding crystallogra phic cha racteristics,including invariant line,habit plane and atomic steps,have been characterized by transmission electron micro scopy and the quasi-O-line model.In addition,the models of phase transfo rmation about the intersection are proposed based on transmission mechanisms of dislocations.Our findings enrich the theories of phase transformation and implicate the possibility to fabricate stro nger and tougher steel.展开更多
The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood t...The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood thus far.Here,we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms,which result in an excellent low-temperature toughness of the steel.Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically,especially at low-temperatures.Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects,which produce large quantities of deformation twins,ε_(hcp)-martensite andα'_(bcc)-martensite.Inversely,in the fine-grained steels,the formation of deformation twins and martensite is significantly inhibited,leading to the decrease of impact toughness.Microstructural characterizations also indicate thatε_(hcp)-martensite becomes more stable thanα'_(bcc)-martensite with decreasing temperature,resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature.In the coarse-grained samples under impact deformation at-80℃,ε_(hcp)-martensite transformation,α'_(bcc)-martensite transformation and deformation twinning all occur simultaneously,which greatly improves the toughness of the steel.展开更多
The formation of supported metal/metal oxide single-atom catalysts(SAC),as well as their structural evolution during catalytic reactions have attracted much research interest in the fields of both inorganic chemistry ...The formation of supported metal/metal oxide single-atom catalysts(SAC),as well as their structural evolution during catalytic reactions have attracted much research interest in the fields of both inorganic chemistry and catalysis recently.In this work,we report the synthesis of iron(ca.10 at%)oxide catalysts with the doping of a small amount(0.5-0.6 at%)of ruthenium oxide,which have been deposited onto the surface of ceria nanorods by an optimized deposition-precipitation(DP)route.Multiple characterization studies including X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM)and nitrogen adsorption/desorption confirmed the identical structural and textural properties of the ceria support after the DP step.Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)combined with electron energy loss spectroscopy(EELS)showed the formation of subnanometer iron species in the fresh samples.Furthermore,the X-ray absorption fine structure(XAFS)technique with the help of related data analysis verified the generation of noncrystalline iron oxide clusters predominantly composed of Fe^(3+)ions.Here,the addition of a secondary metal(ruthenium)greatly promoted the dispersion of Fe over the ceria nanorods.After the catalytic reaction of Fischer-Tropsch synthesis(FTS),the transformation from subnanometer iron oxide species to ionic Fe^(δ+)single atoms has been revealed and confirmed by the corresponding profile fits on the extended X-ray absorption fine structure(EXAFS)spectra.In contrast to the normal coarsening process,the FTS conditions(up to 300°C,2 MPa,CO/H_(2)=1/1)did drive the creation of such iron single atoms solely coordinated by oxygen ions.展开更多
Molybdenum(Mo)has been recognized as an essential alloying element of the MP35N(Co_(35.4)Cr_(22.9)Ni_(35.5)Mo_(6.2),at.%)superalloy for enhancing strength and corrosion resistance.However,a full understanding of the a...Molybdenum(Mo)has been recognized as an essential alloying element of the MP35N(Co_(35.4)Cr_(22.9)Ni_(35.5)Mo_(6.2),at.%)superalloy for enhancing strength and corrosion resistance.However,a full understanding of the addition of Mo on microstructure and mechanical properties of the Mo-free parent alloy is lacking.In this work,we consider five(Co_(37.7)Cr_(24.4)Ni_(37.9))_(100-x)Mo_(x)(x=0,0.7,2.0,3.2,and 6.2)alloys,and reveal that yield/tensile strength and ductility are continuously increased for these alloys with increasing Mo content while a single-phase face-centered cubic structure remains unchanged.It is found that strong solid solution strengthening(SSS)is a main domain to the improved yield strength,whereas grain boundaries are found to soften by the Mo addition.The first-principles calculations demonstrate that a severe local lattice distortion contributes to the enhanced SSS,and the grain boundary softening effect is mostly associated with the decreased shear modulus.Both first-principles calculations and scanning transmission electron microscopy observations reveal that the stacking fault energy(SFE)reduces by the Mo addition.The calculated SFE value decreases from 0.4 mJ/m^(2) to-11.8 mJ/m^(2) at 0 K as Mo content increases from 0 at.%to 6.2 at.%,and experimentally measured values of SFE at room temperature for both samples are about 18 mJ/m^(2) and 9 mJ/m^(2),respectively.The reduction of SFE promoted the generation of stacking faults and deformation twins,which sustain a high strain hardening rate,thus postponing necking instability and enhancing tensile strength and elongation.展开更多
The microstructure of composite diffusion layer of the nitrided and chromized 0.2%carbon steel is investigated using TEM and EDS.It is found that laths of austenite with high nitrogen(γN)precipitate fromα-ferrite ma...The microstructure of composite diffusion layer of the nitrided and chromized 0.2%carbon steel is investigated using TEM and EDS.It is found that laths of austenite with high nitrogen(γN)precipitate fromα-ferrite matrix in the deeper zone of the diffusion layer.TheseγN laths are all twins,with their{111}twinning planes parallel to the lath axis,thus forming a characteristic"back-to-back"morphology.There are two types ofγN lath.The first is a genuinely{111}twin,andγN andαkeep the accurate K-S relationship,and eachγN andαform a sharp and smoothγN/αinter-face of{335}γN//{341}α,namely habit plane{335}fcc.The second is a pseudo-twin,with micro-twins{111}or faults formed within the two twin components.Localized lattice deformation(relaxation)seems to have occurred at the interfaces of the second type ofγN due to the formation of micro-twins or faults within the twin components.These micro-twins or faults make the orientation relationship(OR)between each of theγN and theα-matrix deviate from the accurate K-S OR,and the OR between twoγN twin components deviate from the genuine{111}twin relation-ship.In addition,theγN/αinterface of the second type ofγN is not as sharp or smooth as that of the first one.展开更多
Microalloying elements play a crucial role in mechanical properties and phase stability of metallic alloys.In this work,we employ first-principles calculations and atomic-scale high-angle annular dark-field scanning t...Microalloying elements play a crucial role in mechanical properties and phase stability of metallic alloys.In this work,we employ first-principles calculations and atomic-scale high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)to find promising microalloying elements that will improve the stability and properties ofβ"/Al interface andβ"phase in Al–Mg-Si alloys.First,we define a substitution energy for evaluating the stability ofβ"phase andβ"/Al interface with microalloying elements doped.Then,experiments of HAADF-STEM imaging are carried out to verify the calculational results.Next,using the most stable structures doped with microalloying elements,the mechanical properties of theβ"bulk and theβ"/Al interface were calculated and analyzed.At last,we have figured out the effects of all considered microalloying elements and obtained a rule that the stable occupancy of solute atoms is related to their own radius and the radius of Mg,Si,and Al.These findings will provide some theoretical basis for future microalloying strategies of Al–Mg-Si alloys.展开更多
基金supported financially by the National Natural Science Foundation of China(Nos.51801060,51831004,11427806 and 51671082)the China Postdoctoral Science Foundation(No.2019M652756)+1 种基金the National Key Research and Development Program of China(No.2016YFB0300801)the China Scholarship Council(No.201606130008)。
文摘The crystallography of phase transformation is an important issue for studying metallic alloys.Here,we demonstrate an abnormal orientation relation between face-centered cubic(fcc) and hexagonal closepacked(hcp) phases due to the intersection of two ε_(hcp)-martensite variants in a high manganese steel.The corresponding crystallogra phic cha racteristics,including invariant line,habit plane and atomic steps,have been characterized by transmission electron micro scopy and the quasi-O-line model.In addition,the models of phase transfo rmation about the intersection are proposed based on transmission mechanisms of dislocations.Our findings enrich the theories of phase transformation and implicate the possibility to fabricate stro nger and tougher steel.
基金supported by the National Natural Science Foundation of China[Grant Nos.5180106051831004+6 种基金1142780651671082]the China Postdoctoral Science Foundation(grant number 2019M652756)the National Key Research and Development Program of China(grant number 2016YFB0300801)the China Scholarship Council(grant number 201606130008)the financial support from Austrain Science Fund(FWF)(grant number P 32378-N37)BMBWF(grant number KR 06/2020)。
文摘The high-manganese steels are important structural materials,owing to their excellent toughness at low temperatures.However,the microstructural causes for their unusual properties have not adequately been understood thus far.Here,we report a reversal relationship between impact toughness and grain size in a high-manganese steel and its unrevealed microscopic mechanisms,which result in an excellent low-temperature toughness of the steel.Our investigations show that with increasing grain size the impact toughness of the steel can be improved drastically,especially at low-temperatures.Advanced electron microscopy characterization reveals that the enhanced impact toughness of the coarse-grained steel is attributed to the twinning induced plasticity and transformation induced plasticity effects,which produce large quantities of deformation twins,ε_(hcp)-martensite andα'_(bcc)-martensite.Inversely,in the fine-grained steels,the formation of deformation twins and martensite is significantly inhibited,leading to the decrease of impact toughness.Microstructural characterizations also indicate thatε_(hcp)-martensite becomes more stable thanα'_(bcc)-martensite with decreasing temperature,resulting in characteristic microstructures in the coarse-grained samples after impact deformation at liquid nitrogen temperature.In the coarse-grained samples under impact deformation at-80℃,ε_(hcp)-martensite transformation,α'_(bcc)-martensite transformation and deformation twinning all occur simultaneously,which greatly improves the toughness of the steel.
基金financially supported by the National Science Foundation of China(NSFC)(grant no.21373259)the Excellent Young Scientists Fund from the NSFC(21622106)+2 种基金the Hundred Talents Project of the Chinese Academy of Sciences,the Strategic Priority Research Program of the Chinese Academy of Sciences(grant no.XDA09030102)the Taishan Scholar Project of Shandong Province(China)the Fundamental Research Funds for the Central Universities(China).
文摘The formation of supported metal/metal oxide single-atom catalysts(SAC),as well as their structural evolution during catalytic reactions have attracted much research interest in the fields of both inorganic chemistry and catalysis recently.In this work,we report the synthesis of iron(ca.10 at%)oxide catalysts with the doping of a small amount(0.5-0.6 at%)of ruthenium oxide,which have been deposited onto the surface of ceria nanorods by an optimized deposition-precipitation(DP)route.Multiple characterization studies including X-ray diffraction(XRD),high-resolution transmission electron microscopy(HRTEM)and nitrogen adsorption/desorption confirmed the identical structural and textural properties of the ceria support after the DP step.Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)combined with electron energy loss spectroscopy(EELS)showed the formation of subnanometer iron species in the fresh samples.Furthermore,the X-ray absorption fine structure(XAFS)technique with the help of related data analysis verified the generation of noncrystalline iron oxide clusters predominantly composed of Fe^(3+)ions.Here,the addition of a secondary metal(ruthenium)greatly promoted the dispersion of Fe over the ceria nanorods.After the catalytic reaction of Fischer-Tropsch synthesis(FTS),the transformation from subnanometer iron oxide species to ionic Fe^(δ+)single atoms has been revealed and confirmed by the corresponding profile fits on the extended X-ray absorption fine structure(EXAFS)spectra.In contrast to the normal coarsening process,the FTS conditions(up to 300°C,2 MPa,CO/H_(2)=1/1)did drive the creation of such iron single atoms solely coordinated by oxygen ions.
基金financially supported by the Young Scientists Fund of the National Natural Science Foundation of China(No.52001120)the Hunan Provincial National Science Fund for Distin-guished Young Scholars(No.2022JJ10015)+2 种基金the State Key Labora-tory of Advanced Metals and Materials(No.2021-Z09)the Univer-sity of Science&Technology Beijing,China.X.Q.Li was supported by the Swedish Research Council(No.2020-03736)funded by the Swedish Research Council through grant agreement(No.2018-05973)。
文摘Molybdenum(Mo)has been recognized as an essential alloying element of the MP35N(Co_(35.4)Cr_(22.9)Ni_(35.5)Mo_(6.2),at.%)superalloy for enhancing strength and corrosion resistance.However,a full understanding of the addition of Mo on microstructure and mechanical properties of the Mo-free parent alloy is lacking.In this work,we consider five(Co_(37.7)Cr_(24.4)Ni_(37.9))_(100-x)Mo_(x)(x=0,0.7,2.0,3.2,and 6.2)alloys,and reveal that yield/tensile strength and ductility are continuously increased for these alloys with increasing Mo content while a single-phase face-centered cubic structure remains unchanged.It is found that strong solid solution strengthening(SSS)is a main domain to the improved yield strength,whereas grain boundaries are found to soften by the Mo addition.The first-principles calculations demonstrate that a severe local lattice distortion contributes to the enhanced SSS,and the grain boundary softening effect is mostly associated with the decreased shear modulus.Both first-principles calculations and scanning transmission electron microscopy observations reveal that the stacking fault energy(SFE)reduces by the Mo addition.The calculated SFE value decreases from 0.4 mJ/m^(2) to-11.8 mJ/m^(2) at 0 K as Mo content increases from 0 at.%to 6.2 at.%,and experimentally measured values of SFE at room temperature for both samples are about 18 mJ/m^(2) and 9 mJ/m^(2),respectively.The reduction of SFE promoted the generation of stacking faults and deformation twins,which sustain a high strain hardening rate,thus postponing necking instability and enhancing tensile strength and elongation.
基金Supported by the Research Fund for the Doctoral Program of High Education of China(Grant No.20020561001)the National Natural Science Foundation of China(Grant No.50671038)+1 种基金the Post-Doctoral Program of China(Grant No.20070410979)the Post-Doctoral Program of Hunan Province(Grant No.2006FJ4238)
文摘The microstructure of composite diffusion layer of the nitrided and chromized 0.2%carbon steel is investigated using TEM and EDS.It is found that laths of austenite with high nitrogen(γN)precipitate fromα-ferrite matrix in the deeper zone of the diffusion layer.TheseγN laths are all twins,with their{111}twinning planes parallel to the lath axis,thus forming a characteristic"back-to-back"morphology.There are two types ofγN lath.The first is a genuinely{111}twin,andγN andαkeep the accurate K-S relationship,and eachγN andαform a sharp and smoothγN/αinter-face of{335}γN//{341}α,namely habit plane{335}fcc.The second is a pseudo-twin,with micro-twins{111}or faults formed within the two twin components.Localized lattice deformation(relaxation)seems to have occurred at the interfaces of the second type ofγN due to the formation of micro-twins or faults within the twin components.These micro-twins or faults make the orientation relationship(OR)between each of theγN and theα-matrix deviate from the accurate K-S OR,and the OR between twoγN twin components deviate from the genuine{111}twin relation-ship.In addition,theγN/αinterface of the second type ofγN is not as sharp or smooth as that of the first one.
基金financially supported by the National Natural Science Foundation of China(Nos.52001119,51831004,and 52171006)the Fundamental Research Funds for the Central Universities.
文摘Microalloying elements play a crucial role in mechanical properties and phase stability of metallic alloys.In this work,we employ first-principles calculations and atomic-scale high-angle annular dark-field scanning transmission electron microscopy(HAADF-STEM)to find promising microalloying elements that will improve the stability and properties ofβ"/Al interface andβ"phase in Al–Mg-Si alloys.First,we define a substitution energy for evaluating the stability ofβ"phase andβ"/Al interface with microalloying elements doped.Then,experiments of HAADF-STEM imaging are carried out to verify the calculational results.Next,using the most stable structures doped with microalloying elements,the mechanical properties of theβ"bulk and theβ"/Al interface were calculated and analyzed.At last,we have figured out the effects of all considered microalloying elements and obtained a rule that the stable occupancy of solute atoms is related to their own radius and the radius of Mg,Si,and Al.These findings will provide some theoretical basis for future microalloying strategies of Al–Mg-Si alloys.
