In order to eliminate forging defects appearing in production,based on the rigid-viscoplastic FEM principle,the DEFORM3D software package was employed to simulate the forming process of TC4 alloy mounting part and to ...In order to eliminate forging defects appearing in production,based on the rigid-viscoplastic FEM principle,the DEFORM3D software package was employed to simulate the forming process of TC4 alloy mounting part and to optimize the process parameters.In this simulation,the temperature dependency of the thermal and mechanical properties of material was considered.Based on the simulation,the metal flow and thermomechanical field variables such as stress and damage are obtained.The simulation results show that the forging defects are caused by improper die dimension and the optimized die dimension was proposed.To verify the validity of simulation results,forging experiments were also carried out in a forging plant.The forging experiments show that the optimized die dimension can ensure the quality of forging part,and it can provide reference to improve and optimize die design process.展开更多
The hot deformation behaviors of GCr15 bearing steel were investigated by isothermal compression tests, performed on a Gleeble-3800 thermal-mechanical simulator at temperatures between 950 ℃ and 1 150 ℃ and strain r...The hot deformation behaviors of GCr15 bearing steel were investigated by isothermal compression tests, performed on a Gleeble-3800 thermal-mechanical simulator at temperatures between 950 ℃ and 1 150 ℃ and strain rates between 0.1 and 10 s-1. The peak stress and peak strain as functions of processing parameters were obtained. The dependence of peak stress on strain rate and temperature obeys a hyperbolic sine equation with a Zener-Hollomon parameter. By regression analysis, in the temperature range of 950-1 150 ℃ and strain rate range of 0.1?10 s?1, the mean activation energy and the stress exponent were determined to be 351kJ/mol and 4.728, respectively. Meanwhile, models of flow stress and dynamic recrystallization (DRX) grain size were also established. The model predictions show good agreement with experimental results.展开更多
Temperature is one of the key parameters for BT20 titanium alloy cylindrical workpiece manufactured by vacuum hot bulge forming. A two-dimensional nonlinear thermo-mechanical coupled FE model was established. Numerica...Temperature is one of the key parameters for BT20 titanium alloy cylindrical workpiece manufactured by vacuum hot bulge forming. A two-dimensional nonlinear thermo-mechanical coupled FE model was established. Numerical simulation of vacuum hot bulge forming process of titanium alloy cylindrical workpiece was carried out using FE analysis software MSC Marc. The effects of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece were analyzed by numerical simulation. The simulated results show that the Y-direction displacement and the equivalent plastic strain of the workpiece increase with increasing bulge temperature. The residual stress decreases with increasing bulge temperature. The optimal temperature range of BT20 titanium alloy during vacuum hot bulge forming is 750-850 ℃. The corresponding experiments were carried out. The simulated results agreed well with the experimental results.展开更多
A new reactive magnetron sputtering system enhanced by the faced microwave electron cyclotron resonance plasma source was designed and amorphous CN_(x) films has been prepared by using this system.The character izatio...A new reactive magnetron sputtering system enhanced by the faced microwave electron cyclotron resonance plasma source was designed and amorphous CN_(x) films has been prepared by using this system.The character ization of the films by interference microscopy,atomic force microscopy,and x-ray photoelectron spectroscopy shows that the deposition rate is strongly affected by the direct-current bias,and the films are composed by a single carbon nitride phase and the N/C ratio is 4:3.2,which is close to that of C_(3)N_(4)(4:3).展开更多
Thermal, mechanical and microstructural phenomena are involved in the process of steel quenching. Based on the coupled metallo-thermo-mechanics theory, a calculation model has been developed in this study to simulate ...Thermal, mechanical and microstructural phenomena are involved in the process of steel quenching. Based on the coupled metallo-thermo-mechanics theory, a calculation model has been developed in this study to simulate the quenching process of a gas turbine compressor disk by finite element method. The thermal physical and mechanical properties were treated as a functions of temperature. Moreover, a series of subroutines were developed on the MARC software platform. Consequently, simulated results on temperature, internal stress and distortion during the quenching were illustrated. With the aid of the simulated results, an optimum quenching scheme was proposed. The quenching process simulated in this study appears to be a promising tool in design of heat-treatment processing parameters for gas turbine compressor disks.展开更多
A self-consistent analysis of a pulsed direct-current (DC) N2 glow discharge is presented. The model is based on a numerical solution of the continuity equations for electron and ions coupled with Poisson's equati...A self-consistent analysis of a pulsed direct-current (DC) N2 glow discharge is presented. The model is based on a numerical solution of the continuity equations for electron and ions coupled with Poisson's equation. The spatial-temporal variations of ionic and electronic densities and electric field are obtained. The electric field structure exhibits all the characteristic regions of a typical glow discharge (the cathode fall, the negative glow, and the positive column). Current-voltage characteristics of the discharge can be obtained from the model. The calculated current-voltage results using a constant secondary electron emission coefficient for the gas pressure 133.32 Pa are in reasonable agreement with experiment.展开更多
The synthesis of covalent carbon nitride films becomes an important subject in the materials research field.As a new synthetic method two low-energy(400 and 1000eV)nitrogen ion beams are used to bombard on C_(60) thin...The synthesis of covalent carbon nitride films becomes an important subject in the materials research field.As a new synthetic method two low-energy(400 and 1000eV)nitrogen ion beams are used to bombard on C_(60) thin films individually.The bombarded films are used for Raman and x-ray photoelectron spectroscopy(XPS)measurements.The results of the analyses show that under the bombardment of 400eV nitrogen ion beam,the film still contains a large amount of undestructed C_(60) molecules.In the case of l000eV bombardment,only a little amount of C_(60) molecules is kept undestructed.The experimental results also show that the destructed carbon species will combine chemically with nitrogen ions to form stable covalent carbon nitride,confirmed by the Raman peaks of,e.g.,2240cm-1.The XPS Nls and Cls lines also indicate the formation of covalent carbon nitride in the bombarded films.展开更多
A particle-in-cell simulation is developed to study dc plasma immersion ion implantation. Particular attention is paid to the influence of the voltage applied to the target on the ion path, and the ion flux distributi...A particle-in-cell simulation is developed to study dc plasma immersion ion implantation. Particular attention is paid to the influence of the voltage applied to the target on the ion path, and the ion flux distribution on the target surface. It is found that the potential near the aperture within the plasma region is not the plasma potential, and is impacted by the voltage applied to the implanted target. A curved equipotential contour expands into the plasma region through the aperture and the extent of the expansion depends on the voltage. Ions accelerated by the electric field in the sheath form a beam shape and a flux distribution on the target surface, which are strongly dependent on the applied voltage. The results of the simulations demonstrate the formation mechanism of the grid-shadow effect, which is in agreement with the result observed experimentally.展开更多
For ZnO/diamond structured surface acoustic wave （SAW） filters, performance is sensitively dependent on the quality of the ZnO films. In this paper, we prepare highly-oriented and fine grained polycrystalline ZnO th...For ZnO/diamond structured surface acoustic wave （SAW） filters, performance is sensitively dependent on the quality of the ZnO films. In this paper, we prepare highly-oriented and fine grained polycrystalline ZnO thin films with excellent surface smoothness on the smooth nucleation surfaces of freestanding CVD diamond films by metal organic chemical vapour deposition （MOCVD）. The properties of the ZnO films are characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, and photoluminescence （PL） spectrum. The influences of the deposition conditions on the quality of ZnO films are discussed briefly. ZnO/freestanding thick-diamond-film layered SAW devices with high response frequencies are expected to be developed.展开更多
The inertia friction welding process is a non-linear process because of the interaction between the temperature field and the material properties as well as the friction force. A thermo-mechanical coupled finite eleme...The inertia friction welding process is a non-linear process because of the interaction between the temperature field and the material properties as well as the friction force. A thermo-mechanical coupled finite element model is established to simulate the temperature field of this process. The transient temperature distribution during the inertia friction welding process of two similar workpieces of GH4169 alloy is calculated. The region of the circular cross-section of the workpiece is divided into a number of four-nodded isoparametric elements. In this model, the temperature dependent thermal properties, time dependent heat inputs, contact condition of welding interface, and deformation of the flash were considered. At the same time, the convection and radiation heat losses at the surface of the workpieces were also considered. A temperature data acquisition system was developed. The temperature at some position near the welding interface was measured using this system. The calculated temperature agrees well with the experimental data. The deformation of the flash and the factor affecting the temperature distribution at the welding interface are also discussed.展开更多
This paper presents the interactions between two cold atmospheric plasma jets. By changing the experimental conditions including the gas flow rate, the applied voltage, the power supply frequency and the inter-electro...This paper presents the interactions between two cold atmospheric plasma jets. By changing the experimental conditions including the gas flow rate, the applied voltage, the power supply frequency and the inter-electrode distance d, three different interaction modes, attraction, repulsion and combination, were observed. It is shown that the interaction modes of the two jets are principally affected by the electrodes, the gas flow rate, the plasma jets and the power supply frequency.展开更多
Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experiment...Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experimentally. A critical frequency of 1 kHz was found. With the frequency above 1 kHz, when a fast airflow was introduced into the discharge gap, the discharge patterns varied from filaments to curved stripes and the curvature degree rose with an increase in the airflow speed. At the same time, the discharge intensity decreased. However with the discharge frequency below 1 kHz, the discharge intensity would get greater with an increase in the airflow speed.展开更多
Al-Si alloy coatings were prepared on AZ91HP magnesium alloy by broad-beam laser cladding; the influences of the powers on the microstructure and properties of the coatings were discussed. It was found that the micros...Al-Si alloy coatings were prepared on AZ91HP magnesium alloy by broad-beam laser cladding; the influences of the powers on the microstructure and properties of the coatings were discussed. It was found that the microstructure of the coatings at the powers of 3 and 3.5 kW was characterized by Mg2Si dendrites, and needle-like Mg2Al3 （hcp） dispersing in the Mg17Al12 matrix, whereas the coating at the power of 2.5 kW was composed of the petal-like Mg2Al3 （fcc） as well as the needle-like Mg2Al3 （hcp）. The coating at the power of 4 kW appeared as α-Mg solid solution and Mg2Si, Mg17Al12, as well as Mg2Al3 （hcp）. The coatings with the powers of 3 and 3.5 kW exhibited higher microhardness and better wear resistance because of more Mg2Si and Mg17Al12. However, the coating at the power of 2.5 kW displayed better corrosion resistance.展开更多
The surface modification of magnesium alloys (AZ31 and AZ91HP) was studied by a high current pulsed electron beam(HCPEB). The results show that the cross-sectional microhardness of treated samples increases not only i...The surface modification of magnesium alloys (AZ31 and AZ91HP) was studied by a high current pulsed electron beam(HCPEB). The results show that the cross-sectional microhardness of treated samples increases not only in the heat affected zone(HAZ), but also beyond HAZ, reaching over 250μm. This is due to the action of quasi-static thermal stress and the shock thermal stress wave with materials, which result in its fast deformation on the surface layer and so increases microhardness. For the AZ91HP alloy, a nearly complete dissolution of the intermetallic phase Mg_ 17Al_ 12 is observed, and a super-saturated solid solution forms on the re-melted surface, which is due to the solute trapping effect during the fast solidification process. Measurements on sliding wear show that wear resistance is improved by approximately 5.6 and 2.4 times for the AZ31 and AZ91HP respectively, as compared with as-received samples.展开更多
Using molecular statistics simulations based on the embedded atom method potential, we investigate the reliability of the lateral manipulation of single Pt adatom on Pt（111） surface with a single-atom tip for differ...Using molecular statistics simulations based on the embedded atom method potential, we investigate the reliability of the lateral manipulation of single Pt adatom on Pt（111） surface with a single-atom tip for different tip heights （tip-surface distance） and tip orientations. In the higher tip-height range, tip orientation has little influence on the reliability of the manipulation, and there is an optimal manipulation reliability in this range. In the lower tip- height range the reliability is sensitive to the tip orientation, suggesting that we can obtain a better manipulation reliability with a proper tip orientation. These results can also be extended to the lateral manipulation of Pd adatom on P d （111） surface.展开更多
Based on the voltage and current fluctuating phenomenon in the arc plasma load under the negative-pulse-bias, usingthe plasma physics theory and analysis of computer simulation expatiates that the nature of plasma loa...Based on the voltage and current fluctuating phenomenon in the arc plasma load under the negative-pulse-bias, usingthe plasma physics theory and analysis of computer simulation expatiates that the nature of plasma load in vacuumarc plasma is a capacitance load caused by plasma sheath and can be simplified as a parallel unit composed of acapacitor and a resistor, which have exact and quantitative description in the plasma physics theory. It concludes thevalues of capacitance and resistance are thousand PF and hundred ohm from the result of simulation and experiment.As a result, this has solved the key theoretical issues for the design of negative-pulse-bias source specifically used forvacuum arc ion plating.展开更多
High current pulsed electron beam(HCPEB) is now developing as a useful tool for surface modification of materials.When concentrated electron flux transferring its energy into the surface layer of target material withi...High current pulsed electron beam(HCPEB) is now developing as a useful tool for surface modification of materials.When concentrated electron flux transferring its energy into the surface layer of target material within a short pulse time,coupled thermal and stress processes would lead to the formation of metastalbe microstructure with improved properties.In the present work,HCPEB treatment of 316L stainless steel(SS) was carried out and the microstructural changes in modified surface layer were characterized with optical microscopy,X-ray diffractometry and electron backscatter diffractometry(EBSD) techniques.The corrosion resistance of modified surface was measured in a 5wt.% salt solution.The evolution regularity of surface craters and grain refinement effect,as well as the preferred orientation of(111) crystal plane occurring in the HCPEB treatment under different working parameters were discussed along with their influence on corrosion resistance.展开更多
Dielectric barrier discharge plasma in air was used to modify glass surface to induce the graft of silane onto the treated surface to increase the possibility of biomolecule immobilization. The plasma treated glass ha...Dielectric barrier discharge plasma in air was used to modify glass surface to induce the graft of silane onto the treated surface to increase the possibility of biomolecule immobilization. The plasma treated glass had been characterized by scanning electron microscopy （SEM）, Fourier transform infrared attenuated total reflection spectroscopy, X-ray photoelectron spectroscopy （XPS） and surface water contact angle measurement. The validity of grafting silane onto glass surface was approved by the analysis of water contact angle measurement, SEM and XPS. The grafted silane content was measured by visible absorption spectroscopy using acid Orange-7. It is shown that the grafting density of silane for glass samples increases significantly after plasma treatment.展开更多
The structure and microstructure of constituent phases in annealed IQC100-xDQCx alloys, made from mixtures of (Al62Cu25.5Fe12.5) icosahedral quasicrystal （IQC） and (Al70Co15Ni15) decagonal quasicrystal （DQC）, were...The structure and microstructure of constituent phases in annealed IQC100-xDQCx alloys, made from mixtures of (Al62Cu25.5Fe12.5) icosahedral quasicrystal （IQC） and (Al70Co15Ni15) decagonal quasicrystal （DQC）, were studied by X-ray diffractometry（XRD）, scanning electron microscopy （SEM）, and energy-dispersive X-ray spectroscopy （EDAX）. These constituent phases are mostly approximants: λ, β and τ3. In addition, an Al-Cu-Co DQC phase is observed in (IQC80DQC20) alloy. The nature of these approximants and their relationship with the quasicrystals（QCs） are discussed; and the evolution of these phases is interpreted by the shifting of their e/a-constant lines in the Al-（Cu, Ni）-（Fe, Co） pseudo-ternary phase diagrams.展开更多
At the ambient temperature and pressure a glow discharge plasma was used as a new approach for the coupling of methane with the newly-developed rotary multidentate helix electrode. In the presence of hydrogen, the eff...At the ambient temperature and pressure a glow discharge plasma was used as a new approach for the coupling of methane with the newly-developed rotary multidentate helix electrode. In the presence of hydrogen, the effects of the input peak voltages and gas flow rates on methane conversion, C2 single pass yield and selectivity were investigated, and then the results were compared with those from the three-disc multidentate electrode. This demonstrated, on an experimental scale, that the rotary multidentate helix electrode was better than the multidentate three-disc electrode as there was little accumulation of coke, and the C2 yield per pass was 69.85% and C2 selectivity over 99.14% with 70.46% methane conversion at an input peak voltage of 2300 V and 60 ml/min gas flow rate.展开更多
基金Project(2005400201) supported by the Aeronautical Science Foundation of Liaoning Province,China
文摘In order to eliminate forging defects appearing in production,based on the rigid-viscoplastic FEM principle,the DEFORM3D software package was employed to simulate the forming process of TC4 alloy mounting part and to optimize the process parameters.In this simulation,the temperature dependency of the thermal and mechanical properties of material was considered.Based on the simulation,the metal flow and thermomechanical field variables such as stress and damage are obtained.The simulation results show that the forging defects are caused by improper die dimension and the optimized die dimension was proposed.To verify the validity of simulation results,forging experiments were also carried out in a forging plant.The forging experiments show that the optimized die dimension can ensure the quality of forging part,and it can provide reference to improve and optimize die design process.
基金Project(2001-122) supported by the Youth Science and Technology Elitist Foundation of Dalian, China
文摘The hot deformation behaviors of GCr15 bearing steel were investigated by isothermal compression tests, performed on a Gleeble-3800 thermal-mechanical simulator at temperatures between 950 ℃ and 1 150 ℃ and strain rates between 0.1 and 10 s-1. The peak stress and peak strain as functions of processing parameters were obtained. The dependence of peak stress on strain rate and temperature obeys a hyperbolic sine equation with a Zener-Hollomon parameter. By regression analysis, in the temperature range of 950-1 150 ℃ and strain rate range of 0.1?10 s?1, the mean activation energy and the stress exponent were determined to be 351kJ/mol and 4.728, respectively. Meanwhile, models of flow stress and dynamic recrystallization (DRX) grain size were also established. The model predictions show good agreement with experimental results.
文摘Temperature is one of the key parameters for BT20 titanium alloy cylindrical workpiece manufactured by vacuum hot bulge forming. A two-dimensional nonlinear thermo-mechanical coupled FE model was established. Numerical simulation of vacuum hot bulge forming process of titanium alloy cylindrical workpiece was carried out using FE analysis software MSC Marc. The effects of temperature on vacuum hot bulge forming of BT20 titanium alloy cylindrical workpiece were analyzed by numerical simulation. The simulated results show that the Y-direction displacement and the equivalent plastic strain of the workpiece increase with increasing bulge temperature. The residual stress decreases with increasing bulge temperature. The optimal temperature range of BT20 titanium alloy during vacuum hot bulge forming is 750-850 ℃. The corresponding experiments were carried out. The simulated results agreed well with the experimental results.
基金Supported by the National Natural Science Foundation of China under Grant No.19835030.
文摘A new reactive magnetron sputtering system enhanced by the faced microwave electron cyclotron resonance plasma source was designed and amorphous CN_(x) films has been prepared by using this system.The character ization of the films by interference microscopy,atomic force microscopy,and x-ray photoelectron spectroscopy shows that the deposition rate is strongly affected by the direct-current bias,and the films are composed by a single carbon nitride phase and the N/C ratio is 4:3.2,which is close to that of C_(3)N_(4)(4:3).
文摘Thermal, mechanical and microstructural phenomena are involved in the process of steel quenching. Based on the coupled metallo-thermo-mechanics theory, a calculation model has been developed in this study to simulate the quenching process of a gas turbine compressor disk by finite element method. The thermal physical and mechanical properties were treated as a functions of temperature. Moreover, a series of subroutines were developed on the MARC software platform. Consequently, simulated results on temperature, internal stress and distortion during the quenching were illustrated. With the aid of the simulated results, an optimum quenching scheme was proposed. The quenching process simulated in this study appears to be a promising tool in design of heat-treatment processing parameters for gas turbine compressor disks.
基金The project supported by the National Nature Science Foundation of China (No. 10275010)
文摘A self-consistent analysis of a pulsed direct-current (DC) N2 glow discharge is presented. The model is based on a numerical solution of the continuity equations for electron and ions coupled with Poisson's equation. The spatial-temporal variations of ionic and electronic densities and electric field are obtained. The electric field structure exhibits all the characteristic regions of a typical glow discharge (the cathode fall, the negative glow, and the positive column). Current-voltage characteristics of the discharge can be obtained from the model. The calculated current-voltage results using a constant secondary electron emission coefficient for the gas pressure 133.32 Pa are in reasonable agreement with experiment.
基金Supported by the National Natural Science Foundation of China under Grant No.59472026Shanghai Foundation of Natural Science under Grant No.95ZE14007.
文摘The synthesis of covalent carbon nitride films becomes an important subject in the materials research field.As a new synthetic method two low-energy(400 and 1000eV)nitrogen ion beams are used to bombard on C_(60) thin films individually.The bombarded films are used for Raman and x-ray photoelectron spectroscopy(XPS)measurements.The results of the analyses show that under the bombardment of 400eV nitrogen ion beam,the film still contains a large amount of undestructed C_(60) molecules.In the case of l000eV bombardment,only a little amount of C_(60) molecules is kept undestructed.The experimental results also show that the destructed carbon species will combine chemically with nitrogen ions to form stable covalent carbon nitride,confirmed by the Raman peaks of,e.g.,2240cm-1.The XPS Nls and Cls lines also indicate the formation of covalent carbon nitride in the bombarded films.
文摘A particle-in-cell simulation is developed to study dc plasma immersion ion implantation. Particular attention is paid to the influence of the voltage applied to the target on the ion path, and the ion flux distribution on the target surface. It is found that the potential near the aperture within the plasma region is not the plasma potential, and is impacted by the voltage applied to the implanted target. A curved equipotential contour expands into the plasma region through the aperture and the extent of the expansion depends on the voltage. Ions accelerated by the electric field in the sheath form a beam shape and a flux distribution on the target surface, which are strongly dependent on the applied voltage. The results of the simulations demonstrate the formation mechanism of the grid-shadow effect, which is in agreement with the result observed experimentally.
文摘For ZnO/diamond structured surface acoustic wave （SAW） filters, performance is sensitively dependent on the quality of the ZnO films. In this paper, we prepare highly-oriented and fine grained polycrystalline ZnO thin films with excellent surface smoothness on the smooth nucleation surfaces of freestanding CVD diamond films by metal organic chemical vapour deposition （MOCVD）. The properties of the ZnO films are characterized by x-ray diffraction （XRD）, scanning electron microscopy （SEM）, and photoluminescence （PL） spectrum. The influences of the deposition conditions on the quality of ZnO films are discussed briefly. ZnO/freestanding thick-diamond-film layered SAW devices with high response frequencies are expected to be developed.
文摘The inertia friction welding process is a non-linear process because of the interaction between the temperature field and the material properties as well as the friction force. A thermo-mechanical coupled finite element model is established to simulate the temperature field of this process. The transient temperature distribution during the inertia friction welding process of two similar workpieces of GH4169 alloy is calculated. The region of the circular cross-section of the workpiece is divided into a number of four-nodded isoparametric elements. In this model, the temperature dependent thermal properties, time dependent heat inputs, contact condition of welding interface, and deformation of the flash were considered. At the same time, the convection and radiation heat losses at the surface of the workpieces were also considered. A temperature data acquisition system was developed. The temperature at some position near the welding interface was measured using this system. The calculated temperature agrees well with the experimental data. The deformation of the flash and the factor affecting the temperature distribution at the welding interface are also discussed.
基金supported by National Natural Science Foundation of China (Nos.50537020,50528707)
文摘This paper presents the interactions between two cold atmospheric plasma jets. By changing the experimental conditions including the gas flow rate, the applied voltage, the power supply frequency and the inter-electrode distance d, three different interaction modes, attraction, repulsion and combination, were observed. It is shown that the interaction modes of the two jets are principally affected by the electrodes, the gas flow rate, the plasma jets and the power supply frequency.
基金supported by National Natural Science Foundation of China (Nos. 50537020, 50528707 and 10775027)
文摘Effect of airflow on the dielectric barrier discharge in ambient air at atmospheric pressure is presented. The influence of airflow on the spatial distribution and intensity of a discharge were investigated experimentally. A critical frequency of 1 kHz was found. With the frequency above 1 kHz, when a fast airflow was introduced into the discharge gap, the discharge patterns varied from filaments to curved stripes and the curvature degree rose with an increase in the airflow speed. At the same time, the discharge intensity decreased. However with the discharge frequency below 1 kHz, the discharge intensity would get greater with an increase in the airflow speed.
基金supported by the Chinese Post-Doctoral Fund (No.20070421011)the Jiangsu Province Post-Doctoral Fund (No.0702029B)
文摘Al-Si alloy coatings were prepared on AZ91HP magnesium alloy by broad-beam laser cladding; the influences of the powers on the microstructure and properties of the coatings were discussed. It was found that the microstructure of the coatings at the powers of 3 and 3.5 kW was characterized by Mg2Si dendrites, and needle-like Mg2Al3 （hcp） dispersing in the Mg17Al12 matrix, whereas the coating at the power of 2.5 kW was composed of the petal-like Mg2Al3 （fcc） as well as the needle-like Mg2Al3 （hcp）. The coating at the power of 4 kW appeared as α-Mg solid solution and Mg2Si, Mg17Al12, as well as Mg2Al3 （hcp）. The coatings with the powers of 3 and 3.5 kW exhibited higher microhardness and better wear resistance because of more Mg2Si and Mg17Al12. However, the coating at the power of 2.5 kW displayed better corrosion resistance.
文摘The surface modification of magnesium alloys (AZ31 and AZ91HP) was studied by a high current pulsed electron beam(HCPEB). The results show that the cross-sectional microhardness of treated samples increases not only in the heat affected zone(HAZ), but also beyond HAZ, reaching over 250μm. This is due to the action of quasi-static thermal stress and the shock thermal stress wave with materials, which result in its fast deformation on the surface layer and so increases microhardness. For the AZ91HP alloy, a nearly complete dissolution of the intermetallic phase Mg_ 17Al_ 12 is observed, and a super-saturated solid solution forms on the re-melted surface, which is due to the solute trapping effect during the fast solidification process. Measurements on sliding wear show that wear resistance is improved by approximately 5.6 and 2.4 times for the AZ31 and AZ91HP respectively, as compared with as-received samples.
文摘Using molecular statistics simulations based on the embedded atom method potential, we investigate the reliability of the lateral manipulation of single Pt adatom on Pt（111） surface with a single-atom tip for different tip heights （tip-surface distance） and tip orientations. In the higher tip-height range, tip orientation has little influence on the reliability of the manipulation, and there is an optimal manipulation reliability in this range. In the lower tip- height range the reliability is sensitive to the tip orientation, suggesting that we can obtain a better manipulation reliability with a proper tip orientation. These results can also be extended to the lateral manipulation of Pd adatom on P d （111） surface.
文摘Based on the voltage and current fluctuating phenomenon in the arc plasma load under the negative-pulse-bias, usingthe plasma physics theory and analysis of computer simulation expatiates that the nature of plasma load in vacuumarc plasma is a capacitance load caused by plasma sheath and can be simplified as a parallel unit composed of acapacitor and a resistor, which have exact and quantitative description in the plasma physics theory. It concludes thevalues of capacitance and resistance are thousand PF and hundred ohm from the result of simulation and experiment.As a result, this has solved the key theoretical issues for the design of negative-pulse-bias source specifically used forvacuum arc ion plating.
基金This work is financially supported by Scientific Research Foundation for the Returned Overseas Chinese Scholars and Franco-China Cooperative Research Program between University of Metz and Dalian Uni-versity of Technology(2004)
文摘High current pulsed electron beam(HCPEB) is now developing as a useful tool for surface modification of materials.When concentrated electron flux transferring its energy into the surface layer of target material within a short pulse time,coupled thermal and stress processes would lead to the formation of metastalbe microstructure with improved properties.In the present work,HCPEB treatment of 316L stainless steel(SS) was carried out and the microstructural changes in modified surface layer were characterized with optical microscopy,X-ray diffractometry and electron backscatter diffractometry(EBSD) techniques.The corrosion resistance of modified surface was measured in a 5wt.% salt solution.The evolution regularity of surface craters and grain refinement effect,as well as the preferred orientation of(111) crystal plane occurring in the HCPEB treatment under different working parameters were discussed along with their influence on corrosion resistance.
基金National Natural Science Foundation of China(No.50537020)
文摘Dielectric barrier discharge plasma in air was used to modify glass surface to induce the graft of silane onto the treated surface to increase the possibility of biomolecule immobilization. The plasma treated glass had been characterized by scanning electron microscopy （SEM）, Fourier transform infrared attenuated total reflection spectroscopy, X-ray photoelectron spectroscopy （XPS） and surface water contact angle measurement. The validity of grafting silane onto glass surface was approved by the analysis of water contact angle measurement, SEM and XPS. The grafted silane content was measured by visible absorption spectroscopy using acid Orange-7. It is shown that the grafting density of silane for glass samples increases significantly after plasma treatment.
文摘The structure and microstructure of constituent phases in annealed IQC100-xDQCx alloys, made from mixtures of (Al62Cu25.5Fe12.5) icosahedral quasicrystal （IQC） and (Al70Co15Ni15) decagonal quasicrystal （DQC）, were studied by X-ray diffractometry（XRD）, scanning electron microscopy （SEM）, and energy-dispersive X-ray spectroscopy （EDAX）. These constituent phases are mostly approximants: λ, β and τ3. In addition, an Al-Cu-Co DQC phase is observed in (IQC80DQC20) alloy. The nature of these approximants and their relationship with the quasicrystals（QCs） are discussed; and the evolution of these phases is interpreted by the shifting of their e/a-constant lines in the Al-（Cu, Ni）-（Fe, Co） pseudo-ternary phase diagrams.
基金supported by National Natural Science Foundation of China (No. 50177002)
文摘At the ambient temperature and pressure a glow discharge plasma was used as a new approach for the coupling of methane with the newly-developed rotary multidentate helix electrode. In the presence of hydrogen, the effects of the input peak voltages and gas flow rates on methane conversion, C2 single pass yield and selectivity were investigated, and then the results were compared with those from the three-disc multidentate electrode. This demonstrated, on an experimental scale, that the rotary multidentate helix electrode was better than the multidentate three-disc electrode as there was little accumulation of coke, and the C2 yield per pass was 69.85% and C2 selectivity over 99.14% with 70.46% methane conversion at an input peak voltage of 2300 V and 60 ml/min gas flow rate.
