In order to research the effect of microalloying Nb,the microstructure and heat treatment distortion of case carburizing steels with and without Nb addition are compared.Results show that a uniform and fine prior aust...In order to research the effect of microalloying Nb,the microstructure and heat treatment distortion of case carburizing steels with and without Nb addition are compared.Results show that a uniform and fine prior austenite grain size was obtained for the steel with the addition of 0.03 wt.%Nb even after being carburized at 980℃for 37 h,resulting in a very deep hardened layer of about 4 mm.Nb is an effective microalloying element to hinder austenite grain growth of gears during high-temperature carburizing.Theoretical calculation and experimental observation of NbC precipitates indicate that fine NbC precipitates have not evidently dissolved at 980℃,and thus they can act as grain refiners due to pinning effect.Heat treatment distortion of Nb-added steel is much lower than that of the steel without Nb addition.It may be contributed to its fine and uniform grain size,which presumably influences stress during martensitic transformation.展开更多
The lattice distortion of nanoscale silver particles prepared is studied by using the chemical method. The particles lattice contract was found, and the lattice contraction become greater while the particle size decre...The lattice distortion of nanoscale silver particles prepared is studied by using the chemical method. The particles lattice contract was found, and the lattice contraction become greater while the particle size decreases. The results were explained with surface energy and surface tension.展开更多
The effects of several fluxes on purification,microstructures and properties of A00 aluminum have been studied.The experimental results and analyses indicate that many cracks and large porosities exist in the surface ...The effects of several fluxes on purification,microstructures and properties of A00 aluminum have been studied.The experimental results and analyses indicate that many cracks and large porosities exist in the surface film above the melt purified by C2Cl6 and that the film is floc and mostly composed of Al 2 O 3 and pure aluminum,which carries many carbon particles and AlCl 3 not fully volatilized.And then over 50%(mass fraction) of the all-melting residue is pure aluminum,which is one of the major reasons for high melting loss.Moreover,because of a mass of gas bubbles and a state of seethe,there are many inclusions which size is under 10 μ m in the microstructure of A00 aluminum purified with C2Cl6 or fluxes containing C2Cl6.With this purifying method,the aluminum crystal grains are extended along the radius that was observed firstly and the average crystal size of A00 aluminum are about 100-150 μ m.In addition,small size inclusions have little affected on tensile strength and micro inclusions under 10 μ m have little affected on elongation.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
Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgA...Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99.展开更多
基金the Ministry of Science and Technology(MOST)of China under the contract of No.2016YFB0300102The financial support from CITIC Metals is also acknowledged.
文摘In order to research the effect of microalloying Nb,the microstructure and heat treatment distortion of case carburizing steels with and without Nb addition are compared.Results show that a uniform and fine prior austenite grain size was obtained for the steel with the addition of 0.03 wt.%Nb even after being carburized at 980℃for 37 h,resulting in a very deep hardened layer of about 4 mm.Nb is an effective microalloying element to hinder austenite grain growth of gears during high-temperature carburizing.Theoretical calculation and experimental observation of NbC precipitates indicate that fine NbC precipitates have not evidently dissolved at 980℃,and thus they can act as grain refiners due to pinning effect.Heat treatment distortion of Nb-added steel is much lower than that of the steel without Nb addition.It may be contributed to its fine and uniform grain size,which presumably influences stress during martensitic transformation.
文摘The lattice distortion of nanoscale silver particles prepared is studied by using the chemical method. The particles lattice contract was found, and the lattice contraction become greater while the particle size decreases. The results were explained with surface energy and surface tension.
基金the Natural Science Foundation of Education Department of Jiangsu Province (No.05KJB430102)the Natural Science Foundation of Nantong University(Nos.11ZY007 and 11C001)
文摘The effects of several fluxes on purification,microstructures and properties of A00 aluminum have been studied.The experimental results and analyses indicate that many cracks and large porosities exist in the surface film above the melt purified by C2Cl6 and that the film is floc and mostly composed of Al 2 O 3 and pure aluminum,which carries many carbon particles and AlCl 3 not fully volatilized.And then over 50%(mass fraction) of the all-melting residue is pure aluminum,which is one of the major reasons for high melting loss.Moreover,because of a mass of gas bubbles and a state of seethe,there are many inclusions which size is under 10 μ m in the microstructure of A00 aluminum purified with C2Cl6 or fluxes containing C2Cl6.With this purifying method,the aluminum crystal grains are extended along the radius that was observed firstly and the average crystal size of A00 aluminum are about 100-150 μ m.In addition,small size inclusions have little affected on tensile strength and micro inclusions under 10 μ m have little affected on elongation.
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Project supported by the National Natural Science Foundation of China(Grant No.11675255)the National Key R&D Program of China(Grant No.2016YFA0401503).
文摘Nanostructuring, structure distortion, and/or disorder are the main manipulation techniques to reduce the lattice thermal conductivity and improve the figure of merit of thermoelectric materials. A single-phase α-MgAgSb sample, MgAg0.97Sb0.99, with high thermoelectric performance in near room temperature region was synthesized through a high-energy ball milling with a hot-pressing method. Here, we report the average grain size of 24–28 nm and the accurate structure distortion, which are characterized by high-resolution neutron diffraction and synchrotron x-ray diffraction with Rietveld refinement data analysis. Both the small grain size and the structure distortion have a contribution to the low lattice thermal conductivity in MgAg0.97Sb0.99.
