The hot compressive deformation behaviors of Cu-6wt.%Ag alloy were studied experimentally in the temperature range of 973.1123 K and the strain rate range of 0.01.10 s^-1.The stress increases and reaches the maximum v...The hot compressive deformation behaviors of Cu-6wt.%Ag alloy were studied experimentally in the temperature range of 973.1123 K and the strain rate range of 0.01.10 s^-1.The stress increases and reaches the maximum value when the true strain is very small,and then the stress changes slowly and tends to be stable under the action of work hardening,dynamic recovery and recrystallization.The material parameters of the conventional Arrhenius constitutive model are only related to strain under different deformation conditions,and the prediction error is large,which cannot accurately characterize the hot deformation behavior of the alloy.To describe the hot deformation behavior of the alloy accurately,a modified constitutive model was established by considering the simultaneous influence of forming temperature,strain rate and strain.The results indicate that correlation coefficient(R)and the average absolute relative error(AARE)are 0.993 and 4.2%,respectively.The modified constitutive model can accurately describe the hot deformation behavior of Cu-6wt.%Ag alloy.展开更多
The Cu-10Ag and Cu-10Ag-RE （RE=Ce, Y） alloys in situ filamentary composites were prepared. The relationships of the ultimate tensile strengths （UTS） and microstructure changes of the composites were studied. With ...The Cu-10Ag and Cu-10Ag-RE （RE=Ce, Y） alloys in situ filamentary composites were prepared. The relationships of the ultimate tensile strengths （UTS） and microstructure changes of the composites were studied. With increasing of the true strain η, the sizes of the Ag filaments in the composites reduce according to a negative exponential function of η:d=d0·exp（-0.228η）, and the UTS of the composites increase also according to a exponential function of η, σ Cu/Ag=σ 0（Cu）+[k Cu/Agd0 -1/2]exp（η/3）, here d0 is a coefficient related to the original size of Ag phase. The strain strengthening follows a two-stage strengthening effect. The strengthening mechanisms are related to changes of microstructure in the deformation process. At the low true strain stage, the strengthening is mainly caused by the working hardening controlled by dislocation increasing; at the high true strain stage, the strengthening is mainly caused by the super-fine Ag filaments and the large coherent interfaces between the Ag filaments and Cu matrix. The trace RE additions and the rapid solidification obviously refine scales of the Ag filament of the composites, and therefore obviously increased the strain strengthening rate. The microstructure refinement of the composites, especially the refinement of Ag filament, is the main reason of the high strain strengthening effect in Cu-Ag alloy in situ filamentary composites.展开更多
For Gu-Ag alloy, an important parameter called workability in the forming process of materials can be evaluated by processing maps yielded from the stress-strain data generated by hot compression tests at temperatures...For Gu-Ag alloy, an important parameter called workability in the forming process of materials can be evaluated by processing maps yielded from the stress-strain data generated by hot compression tests at temperatures of 700-850 °C and strain rates of 0.01-10 s-1. And at the true strain of 0.15, 0.35 and 0.55, respectively, the responses of strain-rate sensitivity, power dissipation efficiency and instability parameter to temperature and strain rate were studied. Instability maps and power dissipation maps were superimposed to form processing maps, which reveal the determinate regions where individual metallurgical processes occur and the limiting conditions of flow instability regions. Furthermore, the optimal processing parameters for bulk metal working are identified clearly by the processing maps.展开更多
Developing bimetallic catalysts is an effective strategy for enhancing the activity and selectivity of electrochemical CO_(2) reduction reactions,where understanding the structure-activity relationship is essential fo...Developing bimetallic catalysts is an effective strategy for enhancing the activity and selectivity of electrochemical CO_(2) reduction reactions,where understanding the structure-activity relationship is essential for catalyst design.Herein,we prepared two Cu-Ag bimetallic catalysts with Ag nanoparticles attached to the top or the bottom of Cu nanowires.When tested in a flow cell,the Cu-Ag catalyst with Ag nanoparticles on the bottom achieved a faradaic efficiency of 54%for ethylene production,much higher than the catalyst with Ag nanoparticles on the top.The catalysts were further studied in the H-cell and zero-gap MEA cell.It was found that placing the two metals in the intensified reaction zone is crucial to triggering the tandem reaction of bimetallic catalysts.Our work elucidates the structure-activity relationship of bimetallic catalysts for CO_(2) reduction and demonstrates the importance of considering both catalyst structures and cell characteristics to achieve high activity and selectivity.展开更多
In the present study,the Cu-(1 wt%-6 wt%)Ag alloys were prepared by melting,forging and wire drawing.The effects of plastic deformation on microstructure evolution and properties of the alloys were investigated.The re...In the present study,the Cu-(1 wt%-6 wt%)Ag alloys were prepared by melting,forging and wire drawing.The effects of plastic deformation on microstructure evolution and properties of the alloys were investigated.The results show that non-equilibrium eutectic colonies exist in the Cu-(3 wt%-6 wt%)Ag alloy and no eutectic colonies in the 1 wt%-2 wt%Ag containing alloys.These eutectic colonies are aligned along the drawing direction and refined with the increase of draw ratio.Attributed to the refinement of eutectic colonies,the Cu-Ag alloy exhibits higher strength with the increase of draw ratio.The Cu-6Ag alloy exhibits excellent comprehensive properties with a strength of 930 MPa and a conductivity of 82%IACS when the draw ratio reaches 5.7.展开更多
Cu-Ag-RE alloys with different Ce contents were prepared by vacuum melting, and microstructure evolution and mechanical properties of Cu-Ag-Ce alloys were investigated by optical microscopy, scanning electronic micros...Cu-Ag-RE alloys with different Ce contents were prepared by vacuum melting, and microstructure evolution and mechanical properties of Cu-Ag-Ce alloys were investigated by optical microscopy, scanning electronic microscopy with electron back-scattered diffraction and tensile test. The results indicated that a columnar to equiaxed transition in cast Cu-Ag-RE alloys was observed due to Ce addition and area of the region with equiaxed grains enlarged with increasing Ce content. Cold-rolled Cu-Ag-RE alloys in annealed condition exhibited a partially or fully recrystallized grain structure depending on the concentration of Ce. The average grain size decreased and texture components changed with increasing Ce content. The main brass-type texture component changed to be copper-type as the Ce content increased from 0.05 wt.% to 1.0 wt.%. The Cu-Ag-RE alloy with 0.2 wt.% Ce showed maximum ultimate tensile strength, while the sample with 1.0 wt.% Ce showed a better comprehensive mechanical property.展开更多
Cu-Ag filamentary microcomposites with different Ag contents were prepared by cold drawing and intermediate heat treatments. The microstructure characterization and filamentary distribution were observed for two-phase...Cu-Ag filamentary microcomposites with different Ag contents were prepared by cold drawing and intermediate heat treatments. The microstructure characterization and filamentary distribution were observed for two-phase alloys under different conditions. The effect of heavy drawing strain on the microstructure evolution of Cu-Ag alloys was investigated. The results show that the microstructure components consist of Cu dendrites, eutectic colonies and secondary Ag precipitates in the alloys containing 6%-24% （mass fraction） Ag. With the increase in Ag content, the eutectic colonies in the microstructure increase and gradually change into a continuous net-like distribution. The Cu dendrites, eutectic colonies and secondary Ag precipitates are elongated in an axial direction and developed into the composite filamentary structure during cold drawing deformation. The eutectic colonies tend to evolve into filamentary bundles. The filamentary diameters decrease with the increase in drawing strain degree for the two-phase alloys, in particular for the alloys with low Ag content. The reduction in filamentary diameters becomes slow once the drawing strain has exceeded a certain level.展开更多
The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for th...The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for the onset of dynamic recrystallization （DRX） were determined based on the conventional strain hardening rate curves （dσ/dε versus σ）.The progress of DRX was analyzed by constructing a model of volume fraction of DRX based on flow curves.The strain rate sensitivity （SRS） and activation volume V were calculated.The results show that the DRX almost can happen under all deformation conditions even at high Z deformations where dynamic recovery （DRV） is the main softening mechanism.The DRX fraction curves can well predict the DRX behavior.The strain has significant effects on SRS at the strain rates of 0.01s-1 and 10s-1 which are mainly due to off-equilibrium saturation of dislocation storage and annihilation while the effects of the temperature on the SRS are based on the uniformity of microstructure distribution.The formation of ＂forest＂ of dislocation is contributed to the low activation volume V＊（about 168b3） which is independent of Z values at the initial deformation.The cross-slip due to dislocation piled up beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions at high strain （ε=0.6） while the fine DRX grains coarsed is the main reason for the high activation volume at low Z under the same strain conditions.展开更多
The in situ filamentary composites based on the Cu-10Ag and Cu-10Ag-Ce alloys were prepared. The microstructure and properties of the composites were studied. The effects of Ce addition on the microstructure as cast, ...The in situ filamentary composites based on the Cu-10Ag and Cu-10Ag-Ce alloys were prepared. The microstructure and properties of the composites were studied. The effects of Ce addition on the microstructure as cast, including refining Cu grains and the Ag filaments, increasing the proportion of (Cu+Ag) eutectic and decreasing the proportion of the Ag precipitate, were researched. The average size of the Ag filaments in the composites could be approached by a formula: d=C·exp(-0.228η), here C is a coefficient related to the size of the original grains and 1500 nm for Cu-10Ag and 800 nm for Cu-10Ag-Ce. A two-stage strain strengthening effect was found for the deformed composites, that is the dislocation strengthening at low strain stage and the ultra-fine Ag filaments or interface strengthening at the high strain stage. The intermediate heat treatment at lower temperature further refined the Ag filaments and therefore improved the properties. The high strengthening rate of Ce addition on Cu-10Ag alloy attributed the refining effect to Cu grains and Ag filaments. The typical properties of the heavy deformed composites with 1 IHT reached to UTS=1500 MPa with conductivity 62% IACS for the Cu-10Ag alloy and UTS=1550 MPa with conductivity 65% IACS for the Cu-10Ag-Ce alloy, respectively.展开更多
Interface has remarkble effects on the properties of metallic materials. However, the study on the interface of two phases has not had a thorough understanding, though many significant improvements have been made in s...Interface has remarkble effects on the properties of metallic materials. However, the study on the interface of two phases has not had a thorough understanding, though many significant improvements have been made in studying the grain boundary. The aim of this note is to conduct a preliminary analysis on Cu-Ag coherent interface using the 'empiric electron theory of solid and molecule' developed by Yu Rui-huang.展开更多
The microstructure evolution of Cu dendrites in Cu-6%Ag alloys by modified unidirectional solidification under a static magnetic field has been investigated experimentally and quantitatively.The results show that the ...The microstructure evolution of Cu dendrites in Cu-6%Ag alloys by modified unidirectional solidification under a static magnetic field has been investigated experimentally and quantitatively.The results show that the proeutectic Cu dendrites are finer when they are closer to the water-cooling copper mould and the unidirectional effect is more obvious,which is attributed to the higher solidification velocity.The quantitative analysis of the microstructure indicates that with increasing external magnetic flux density,the primary arms of the proeutectic Cu dendrites are refined and along a given direction.The analysis indicates that it is both the thermoelectromagnetic convection effect by the external magnetic field and the branch effect of the dendrites.展开更多
The discontinuous precipitation kinetics and mechanism of the α (Ag-rich) phase in Cu-7 wt% Ag alloy has been investigated using dilatometric and calorimetric anisothermal analysis, optical microscopy, scanning and t...The discontinuous precipitation kinetics and mechanism of the α (Ag-rich) phase in Cu-7 wt% Ag alloy has been investigated using dilatometric and calorimetric anisothermal analysis, optical microscopy, scanning and transmission electron microscopy and X-ray diffraction. Dilatometric and calorimetric curves present at ~ 500°C an important effect related to the ? (Ag-rich) phase formation and consequently the matrix β (Cu-rich) depletion. The nucleation and growth of the precipitated phase show cells formation at initial grain boundaries;a fine lamellar structure is detected by SEM and TEM and consists of alternate lamellar of the α (Ag-rich) and β (Cu-rich)-solid solutions. Cellular precipitation leads to the simultaneous appearance of two diffraction peaks and occurs apparently according to the Fournelle and Clark’s mechanism. Obtained results give an Avrami exponent n = 2.0 ± 0.2 in agreement with an interfacial controlled process having an activation energy Ea equals to 99 ± 7 kJ/mol obtained from anisothermal analysis by using different isoconversion methods. This activation energy expresses the discrepancy between isoconversion methods and the analytical diffusive model. Moreover, the supersaturation rate has an effect on the lamella spacing of the precipitated cells.展开更多
The effects of different electromagnetic stirring currents on the microstructures of Cu-6%Ag alloys by applying electromagnetic stirring during solidification process are investigated experimentally.The results show t...The effects of different electromagnetic stirring currents on the microstructures of Cu-6%Ag alloys by applying electromagnetic stirring during solidification process are investigated experimentally.The results show that with increasing stirring current,the macro-microstructural grains of the Cu-Ag alloys are refined gradually and evenly distributed.The observation on the microstructure indicates that the primary Cu dendrites become shorter and thicker,and the secondary dendrites are underdeveloped with small-sized equiaxed dendrites with increasing current.Cu-6%Ag alloys solidified with electromagnetic stirring are drawn to the composite wires with different drawing ratios.The results show that their microstructures are refined along the drawing direction when the stirring current increases from 100 A to 200 A. As the current increases to 350 A,the microstructure is not changed obviously.Correspondingly,the tensile strength of Cu-6%Ag alloys increases and the conductivity reduces with increasing drawing rate.Cu-6%Ag alloys could get the better strength with stirring current of 200 A,which is consistent with the microstructural results.展开更多
I.OCCURRENCE Mercurian silver occurs in the oxidation zone-type Cu-Ag ore deposit around the Shuidong area, Nayong County, Guizhou Province. The Cu-Ag deposit is present in the upper part of the Sinian Dengying Format...I.OCCURRENCE Mercurian silver occurs in the oxidation zone-type Cu-Ag ore deposit around the Shuidong area, Nayong County, Guizhou Province. The Cu-Ag deposit is present in the upper part of the Sinian Dengying Formation dolomite. It is small in size and contains some orebodies which are dispersed in distribution and diverse in shape. Evidence shows展开更多
基金Project(51675061)supported by the National Natural Science Foundation of China
文摘The hot compressive deformation behaviors of Cu-6wt.%Ag alloy were studied experimentally in the temperature range of 973.1123 K and the strain rate range of 0.01.10 s^-1.The stress increases and reaches the maximum value when the true strain is very small,and then the stress changes slowly and tends to be stable under the action of work hardening,dynamic recovery and recrystallization.The material parameters of the conventional Arrhenius constitutive model are only related to strain under different deformation conditions,and the prediction error is large,which cannot accurately characterize the hot deformation behavior of the alloy.To describe the hot deformation behavior of the alloy accurately,a modified constitutive model was established by considering the simultaneous influence of forming temperature,strain rate and strain.The results indicate that correlation coefficient(R)and the average absolute relative error(AARE)are 0.993 and 4.2%,respectively.The modified constitutive model can accurately describe the hot deformation behavior of Cu-6wt.%Ag alloy.
基金The National Natural Science Foundation of China(No:50371031)
文摘The Cu-10Ag and Cu-10Ag-RE （RE=Ce, Y） alloys in situ filamentary composites were prepared. The relationships of the ultimate tensile strengths （UTS） and microstructure changes of the composites were studied. With increasing of the true strain η, the sizes of the Ag filaments in the composites reduce according to a negative exponential function of η:d=d0·exp（-0.228η）, and the UTS of the composites increase also according to a exponential function of η, σ Cu/Ag=σ 0（Cu）+[k Cu/Agd0 -1/2]exp（η/3）, here d0 is a coefficient related to the original size of Ag phase. The strain strengthening follows a two-stage strengthening effect. The strengthening mechanisms are related to changes of microstructure in the deformation process. At the low true strain stage, the strengthening is mainly caused by the working hardening controlled by dislocation increasing; at the high true strain stage, the strengthening is mainly caused by the super-fine Ag filaments and the large coherent interfaces between the Ag filaments and Cu matrix. The trace RE additions and the rapid solidification obviously refine scales of the Ag filament of the composites, and therefore obviously increased the strain strengthening rate. The microstructure refinement of the composites, especially the refinement of Ag filament, is the main reason of the high strain strengthening effect in Cu-Ag alloy in situ filamentary composites.
基金Project(CSTC2009BA4065) supported by the Chongqing Natural Science Foundation,China
文摘For Gu-Ag alloy, an important parameter called workability in the forming process of materials can be evaluated by processing maps yielded from the stress-strain data generated by hot compression tests at temperatures of 700-850 °C and strain rates of 0.01-10 s-1. And at the true strain of 0.15, 0.35 and 0.55, respectively, the responses of strain-rate sensitivity, power dissipation efficiency and instability parameter to temperature and strain rate were studied. Instability maps and power dissipation maps were superimposed to form processing maps, which reveal the determinate regions where individual metallurgical processes occur and the limiting conditions of flow instability regions. Furthermore, the optimal processing parameters for bulk metal working are identified clearly by the processing maps.
基金the funding support from the National Key Research and Development Program of China(2019YFE0123400)the Tianjin Distinguished Young Scholars Fund(20JCJQJC00260)+4 种基金the Major Science and Technology Project of Anhui Province(202203f07020007)the Anhui Conch Group Co.,Ltdthe“111”Project(B16027)the funding support from the Natural Science Foundation of China(22209081)the fellowship of China Postdoctoral Science Foundation(2021M690082)。
文摘Developing bimetallic catalysts is an effective strategy for enhancing the activity and selectivity of electrochemical CO_(2) reduction reactions,where understanding the structure-activity relationship is essential for catalyst design.Herein,we prepared two Cu-Ag bimetallic catalysts with Ag nanoparticles attached to the top or the bottom of Cu nanowires.When tested in a flow cell,the Cu-Ag catalyst with Ag nanoparticles on the bottom achieved a faradaic efficiency of 54%for ethylene production,much higher than the catalyst with Ag nanoparticles on the top.The catalysts were further studied in the H-cell and zero-gap MEA cell.It was found that placing the two metals in the intensified reaction zone is crucial to triggering the tandem reaction of bimetallic catalysts.Our work elucidates the structure-activity relationship of bimetallic catalysts for CO_(2) reduction and demonstrates the importance of considering both catalyst structures and cell characteristics to achieve high activity and selectivity.
基金Funded by the National Key R&D Program of China(Nos.2021YFB2500600 and 2017YFE0301405)the Institute of Electrical Engineering,CAS(Nos.E155710301 and E155710201)+1 种基金the Fundamental Research Funds for the Central Universities of China(No.2020CDJDPT001)the Youth Innovation Promotion Association CAS(No.2022138)。
文摘In the present study,the Cu-(1 wt%-6 wt%)Ag alloys were prepared by melting,forging and wire drawing.The effects of plastic deformation on microstructure evolution and properties of the alloys were investigated.The results show that non-equilibrium eutectic colonies exist in the Cu-(3 wt%-6 wt%)Ag alloy and no eutectic colonies in the 1 wt%-2 wt%Ag containing alloys.These eutectic colonies are aligned along the drawing direction and refined with the increase of draw ratio.Attributed to the refinement of eutectic colonies,the Cu-Ag alloy exhibits higher strength with the increase of draw ratio.The Cu-6Ag alloy exhibits excellent comprehensive properties with a strength of 930 MPa and a conductivity of 82%IACS when the draw ratio reaches 5.7.
基金supported by the Fund of Independent Innovation in Shandong Province(2013CXB60201)the Fund of Transformation of Independent Innovation Achievements in Shandong(2014CGZH0102)the Fundamental Research Fund of Shandong University(2016JC016)
文摘Cu-Ag-RE alloys with different Ce contents were prepared by vacuum melting, and microstructure evolution and mechanical properties of Cu-Ag-Ce alloys were investigated by optical microscopy, scanning electronic microscopy with electron back-scattered diffraction and tensile test. The results indicated that a columnar to equiaxed transition in cast Cu-Ag-RE alloys was observed due to Ce addition and area of the region with equiaxed grains enlarged with increasing Ce content. Cold-rolled Cu-Ag-RE alloys in annealed condition exhibited a partially or fully recrystallized grain structure depending on the concentration of Ce. The average grain size decreased and texture components changed with increasing Ce content. The main brass-type texture component changed to be copper-type as the Ce content increased from 0.05 wt.% to 1.0 wt.%. The Cu-Ag-RE alloy with 0.2 wt.% Ce showed maximum ultimate tensile strength, while the sample with 1.0 wt.% Ce showed a better comprehensive mechanical property.
基金Project (No. 50671092) supported by the National Natural Science Foundation of China
文摘Cu-Ag filamentary microcomposites with different Ag contents were prepared by cold drawing and intermediate heat treatments. The microstructure characterization and filamentary distribution were observed for two-phase alloys under different conditions. The effect of heavy drawing strain on the microstructure evolution of Cu-Ag alloys was investigated. The results show that the microstructure components consist of Cu dendrites, eutectic colonies and secondary Ag precipitates in the alloys containing 6%-24% （mass fraction） Ag. With the increase in Ag content, the eutectic colonies in the microstructure increase and gradually change into a continuous net-like distribution. The Cu dendrites, eutectic colonies and secondary Ag precipitates are elongated in an axial direction and developed into the composite filamentary structure during cold drawing deformation. The eutectic colonies tend to evolve into filamentary bundles. The filamentary diameters decrease with the increase in drawing strain degree for the two-phase alloys, in particular for the alloys with low Ag content. The reduction in filamentary diameters becomes slow once the drawing strain has exceeded a certain level.
基金supported by the Chongqing Natural Science Foundation(No.CSTC2009BA4065)
文摘The work hardening and dynamic softening behaviors of Cu-6 wt pct Ag binary alloy were studied by hot compression tests under temperature range of 700-850℃ at strain rates of 0.01-10s-1.The critical conditions for the onset of dynamic recrystallization （DRX） were determined based on the conventional strain hardening rate curves （dσ/dε versus σ）.The progress of DRX was analyzed by constructing a model of volume fraction of DRX based on flow curves.The strain rate sensitivity （SRS） and activation volume V were calculated.The results show that the DRX almost can happen under all deformation conditions even at high Z deformations where dynamic recovery （DRV） is the main softening mechanism.The DRX fraction curves can well predict the DRX behavior.The strain has significant effects on SRS at the strain rates of 0.01s-1 and 10s-1 which are mainly due to off-equilibrium saturation of dislocation storage and annihilation while the effects of the temperature on the SRS are based on the uniformity of microstructure distribution.The formation of ＂forest＂ of dislocation is contributed to the low activation volume V＊（about 168b3） which is independent of Z values at the initial deformation.The cross-slip due to dislocation piled up beyond the grain boundaries or obstacles is related to the low activation volume under the high Z deformation conditions at high strain （ε=0.6） while the fine DRX grains coarsed is the main reason for the high activation volume at low Z under the same strain conditions.
文摘The in situ filamentary composites based on the Cu-10Ag and Cu-10Ag-Ce alloys were prepared. The microstructure and properties of the composites were studied. The effects of Ce addition on the microstructure as cast, including refining Cu grains and the Ag filaments, increasing the proportion of (Cu+Ag) eutectic and decreasing the proportion of the Ag precipitate, were researched. The average size of the Ag filaments in the composites could be approached by a formula: d=C·exp(-0.228η), here C is a coefficient related to the size of the original grains and 1500 nm for Cu-10Ag and 800 nm for Cu-10Ag-Ce. A two-stage strain strengthening effect was found for the deformed composites, that is the dislocation strengthening at low strain stage and the ultra-fine Ag filaments or interface strengthening at the high strain stage. The intermediate heat treatment at lower temperature further refined the Ag filaments and therefore improved the properties. The high strengthening rate of Ce addition on Cu-10Ag alloy attributed the refining effect to Cu grains and Ag filaments. The typical properties of the heavy deformed composites with 1 IHT reached to UTS=1500 MPa with conductivity 62% IACS for the Cu-10Ag alloy and UTS=1550 MPa with conductivity 65% IACS for the Cu-10Ag-Ce alloy, respectively.
文摘Interface has remarkble effects on the properties of metallic materials. However, the study on the interface of two phases has not had a thorough understanding, though many significant improvements have been made in studying the grain boundary. The aim of this note is to conduct a preliminary analysis on Cu-Ag coherent interface using the 'empiric electron theory of solid and molecule' developed by Yu Rui-huang.
基金Item Sponsored by the National Natural Science Foundation of China[No.51004038 and No.50901019]the Fundamental Research Funds for the Central Universities[No.N090309002]+2 种基金Wuhan National High Magnetic Field Center (Grant No.WHMFCKF2011007) National High Technology Research and Development Program of China (No.2007AA03Z519) the 111 Project of China (No.B07015)
文摘The microstructure evolution of Cu dendrites in Cu-6%Ag alloys by modified unidirectional solidification under a static magnetic field has been investigated experimentally and quantitatively.The results show that the proeutectic Cu dendrites are finer when they are closer to the water-cooling copper mould and the unidirectional effect is more obvious,which is attributed to the higher solidification velocity.The quantitative analysis of the microstructure indicates that with increasing external magnetic flux density,the primary arms of the proeutectic Cu dendrites are refined and along a given direction.The analysis indicates that it is both the thermoelectromagnetic convection effect by the external magnetic field and the branch effect of the dendrites.
文摘The discontinuous precipitation kinetics and mechanism of the α (Ag-rich) phase in Cu-7 wt% Ag alloy has been investigated using dilatometric and calorimetric anisothermal analysis, optical microscopy, scanning and transmission electron microscopy and X-ray diffraction. Dilatometric and calorimetric curves present at ~ 500°C an important effect related to the ? (Ag-rich) phase formation and consequently the matrix β (Cu-rich) depletion. The nucleation and growth of the precipitated phase show cells formation at initial grain boundaries;a fine lamellar structure is detected by SEM and TEM and consists of alternate lamellar of the α (Ag-rich) and β (Cu-rich)-solid solutions. Cellular precipitation leads to the simultaneous appearance of two diffraction peaks and occurs apparently according to the Fournelle and Clark’s mechanism. Obtained results give an Avrami exponent n = 2.0 ± 0.2 in agreement with an interfacial controlled process having an activation energy Ea equals to 99 ± 7 kJ/mol obtained from anisothermal analysis by using different isoconversion methods. This activation energy expresses the discrepancy between isoconversion methods and the analytical diffusive model. Moreover, the supersaturation rate has an effect on the lamella spacing of the precipitated cells.
基金Item Sponsored by the National Natural Science Foundation of China[No.51004038 and No.50901019]the Fundamental Research Funds for the Central Universities[No.N090309002]+2 种基金Wuhan National High Magnetic Field Center (Grant No.WHMFCKF2011007) National High Technology Research and Development Program of China (No.2007AA03Z519) the 111 Project of China (No.B07015)
文摘The effects of different electromagnetic stirring currents on the microstructures of Cu-6%Ag alloys by applying electromagnetic stirring during solidification process are investigated experimentally.The results show that with increasing stirring current,the macro-microstructural grains of the Cu-Ag alloys are refined gradually and evenly distributed.The observation on the microstructure indicates that the primary Cu dendrites become shorter and thicker,and the secondary dendrites are underdeveloped with small-sized equiaxed dendrites with increasing current.Cu-6%Ag alloys solidified with electromagnetic stirring are drawn to the composite wires with different drawing ratios.The results show that their microstructures are refined along the drawing direction when the stirring current increases from 100 A to 200 A. As the current increases to 350 A,the microstructure is not changed obviously.Correspondingly,the tensile strength of Cu-6%Ag alloys increases and the conductivity reduces with increasing drawing rate.Cu-6%Ag alloys could get the better strength with stirring current of 200 A,which is consistent with the microstructural results.
基金Project supported by the National Natural Science Foundation of China
文摘I.OCCURRENCE Mercurian silver occurs in the oxidation zone-type Cu-Ag ore deposit around the Shuidong area, Nayong County, Guizhou Province. The Cu-Ag deposit is present in the upper part of the Sinian Dengying Formation dolomite. It is small in size and contains some orebodies which are dispersed in distribution and diverse in shape. Evidence shows
