A new compact pressurization control system of the low pressure casting machine for crucible pressure casting has been developed. It is especially designed for the production of high-quality aluminum or magnesium allo...A new compact pressurization control system of the low pressure casting machine for crucible pressure casting has been developed. It is especially designed for the production of high-quality aluminum or magnesium alloy parts with low input cost. This machine with such a system has the virtue of economical and compact, and combines the Fuzzy-PID technology and achieves accuracies of ±2.5 mbar. At present, this machine has been adopted by several users in China for the production of aluminum alloy castings with high property requirements. Furthermore, for magnesium alloy castings, this machine can be used with the gas protect unit.展开更多
The mechanical characters of CdZnTe crystal were investigated by nanoscratch tests, and the effects of mechanical anisotropy on the material removal rate and surface quality were studied by polishing tests. There is a...The mechanical characters of CdZnTe crystal were investigated by nanoscratch tests, and the effects of mechanical anisotropy on the material removal rate and surface quality were studied by polishing tests. There is a peak of frictional coefficient at the early stage of scratch, and increasing the vertical force will result in the increase of peak value correspondingly. The fluctuation phenomenon of frictional coefficient is generated at high vertical force. The lateral forces show the apparent twofold and threefold symmetries on （110） and （111） planes, respectively. To obtain high surface quality, low polishing pressure and hard direction （〈 T10 〉 directions on （110） plane and 〈 112 〉 directions on （111） plane） should be selected, and to achieve high material removal rate, high polishing pressure and soft direction （〈001〉 directions on （110） plane and 〈 121 〉 directions on （111） plane） should be selected.展开更多
The resistivity of Hg<sub>0.89</sub>Mn<sub>0.11</sub>Te has been measured by the superconducting quantum interference device magnetometer in the temperature range from 5 to 200 K under the appl...The resistivity of Hg<sub>0.89</sub>Mn<sub>0.11</sub>Te has been measured by the superconducting quantum interference device magnetometer in the temperature range from 5 to 200 K under the applied magnetic field of 1, 2, 4 and 6.5 Tesla, respectively, compared with that of no-magnetic field. The results show that the resistivity increases with increase applied magnetic field at higher temperature from 80 to 200 K, but decreases at lower temperature from 5 to 25 K. There exists a transitive range from 25 to 80 K, where the variation of the resistivity shows different tendencies depending on the strength of magnetic field. Maximum difference of resistivity under 6.5 Tesla from that without magnetic field in the temperature range from 30 to 200 K is only about 5 Ω·cm, but it increases up to 3 orders of magnitude at 5 K. The analysis shows that the variation of resistivity of Hg<sub>0.89</sub>Mn<sub>0.11</sub>Te under the magnetic field is the algebraic sum of the transverse direction magnetoresistance effect and the sp-d exchange interaction effect. TDRME plays major role in the high temperature range. However, with the decrease of temperature, the effect of sp-d EI on the resistivity gradually exceeds that of the transverse direction magnetoresistance effect through the transitive range, and becomes the dominant effect in the temperature range from 5 to 25 K, which leads to the dramatic decrease of resistivity.展开更多
The magnetization of Hg0.89Mn0.11 Te single crystal grown by vertical Bridgman method was studied by using superconducting quantum interference device magnetometer（SQUID Magnetometer）. First, magnetization measureme...The magnetization of Hg0.89Mn0.11 Te single crystal grown by vertical Bridgman method was studied by using superconducting quantum interference device magnetometer（SQUID Magnetometer）. First, magnetization measurements were done under various magnetic fi eld strengths from-20 kOe to 20 kOe at 5 K, 15 K, and 77 K, respectively. Then, the magnetizations were measured with continuous changes of temperature in the range from 5 K to 300 K under the magnetic field of 0.1 kOe and 10 kOe, respectively. The modifi ed Brillouin function was well fitted with the data of magnetization vs. magnetic field strength. The analysis indicated that there was an antiferromagnetic exchange coupling among Mn^2＋ ions. The results of reciprocal susceptibility vs. temperature fi t Curie-Weiss law very well at the temperatures above 40 K, but deviate from the law from 5 Kto 40 K, which shows that the antiferromagnetic exchange coupling among Mn^2＋ ions increases in the lower temperature range below 40 K. The experimental result was explained by extending higher-order terms in the calculation of susceptibility and fitted by a power law function. The measurements reveal that Hg0.89Mn0.11 Te possesses paramagnetic properties at temperatures from 5 K to 300 K.展开更多
The optical microscope, SEM and EDS were adopted to analyze the rheoforming solidification morpholo-gies and microstructures of deformed AZ91D magnesium alloy after isothermal treatment in semisolid state. The re-sult...The optical microscope, SEM and EDS were adopted to analyze the rheoforming solidification morpholo-gies and microstructures of deformed AZ91D magnesium alloy after isothermal treatment in semisolid state. The re-sults show that primary α phase can be formed through attachment growth, when the liquid fraction is small; and primary α phase will grow in dendrites, when the liquid fraction is high. Eutectic solidification is carried out in the ways of both dissociated growth and symbiotic growth, de-pending on the morphology of primary α phase. Liquid with eutectic concentration solidifies into lamina eutectic. During solidification of the liquid pools inside grains, α phase can be formed through attachment growth. The eutectic solidifica-tion was mainly carried out in the dissociated pattern.展开更多
Knowledge of diffusivity is a prerequisite for understanding many scientific and technological disciplines. In this paper, firstly major experimental methods, which are employed to provide various diffusivity data, ar...Knowledge of diffusivity is a prerequisite for understanding many scientific and technological disciplines. In this paper, firstly major experimental methods, which are employed to provide various diffusivity data, are briefly described. Secondly, the fun-damentals of various computational methods, including first-principles method, embedded atomic method/molecular dynamic simulation, semi-empirical approaches, and phenomenological DICTRA technique, are demonstrated. Diffusion models re- cently developed for order/disorder transitions and stoichiometric compounds are also briefly depicted. Thirdly, a newly estab- lished diffusivity database for liquid, fcc_A1, Lie, bcc_A2, bcc_B2, and interrnetallic phases in the multicomponent A1 alloys is presented via a few case studies in binary, ternary and quaternary systems. And the integration of various computational techniques and experimental methods is highlighted. The reliability of this diffusivity database is validated by comparing the calculated and measured concentration profiles, diffusion paths, and Kirkendall shifts in various binary, ternary and quaternary diffusion couples. Next, the established diffusivity databases along with thermodynamic and other thermo-physical properties are utilized to simulate the microstructural evolution for Al alloys during solidification, interdiffusion and precipitation. A spe- cial discussion is presented on the phase-field simulation of interdiffusion microstructures in a series of Ni-Al diffusion couples composed of γ, γ＇, and β phases under the effects of both coherent strain and external compressive force. Future orientations in the establishment of next generation of diffusivity database are finally addressed.展开更多
CdZnTe is an excellent material candidate for high efficiency,high-resolution room-temperature nuclear radiation detectors,and the CdZnTe detectors are being widely used in medicine,industry,safeguard and scientific X...CdZnTe is an excellent material candidate for high efficiency,high-resolution room-temperature nuclear radiation detectors,and the CdZnTe detectors are being widely used in medicine,industry,safeguard and scientific X-ray and γ-ray imaging and spectroscopic applications.In this work,three CdZnTe planar detectors with different grades,named CZT-1,CZT-2 and CZT-3,respectively,were fabricated.And the effects of mobility,lifetime and de-trapping time on the performance of CdZnTe planar detector,such as the energy resolution,charge collection efficiency and peak to valley ratio,were analyzed.The charge collection efficiency depends on the product of carrier mobility and lifetime,which has a great effect on the energy resolution of detector when the efficiency is less than 90%.The de-trapping time of carriers in deep levels should be responsible for the peak to valley ratio and "polarization".展开更多
基金financially supported by the National Natural Science Foundation of China, Project No. 51074210
文摘A new compact pressurization control system of the low pressure casting machine for crucible pressure casting has been developed. It is especially designed for the production of high-quality aluminum or magnesium alloy parts with low input cost. This machine with such a system has the virtue of economical and compact, and combines the Fuzzy-PID technology and achieves accuracies of ±2.5 mbar. At present, this machine has been adopted by several users in China for the production of aluminum alloy castings with high property requirements. Furthermore, for magnesium alloy castings, this machine can be used with the gas protect unit.
基金supported by the Key Project of the National Natural Science Foundation of China (No. 50535020)the Fund of the State Key Laboratory of Solidification Processing in Northwestern Polytechnical University (No. SKLSP200902)
文摘The mechanical characters of CdZnTe crystal were investigated by nanoscratch tests, and the effects of mechanical anisotropy on the material removal rate and surface quality were studied by polishing tests. There is a peak of frictional coefficient at the early stage of scratch, and increasing the vertical force will result in the increase of peak value correspondingly. The fluctuation phenomenon of frictional coefficient is generated at high vertical force. The lateral forces show the apparent twofold and threefold symmetries on （110） and （111） planes, respectively. To obtain high surface quality, low polishing pressure and hard direction （〈 T10 〉 directions on （110） plane and 〈 112 〉 directions on （111） plane） should be selected, and to achieve high material removal rate, high polishing pressure and soft direction （〈001〉 directions on （110） plane and 〈 121 〉 directions on （111） plane） should be selected.
基金Supported by the National Natural Science Foundation of China(No.50336040)
文摘The resistivity of Hg<sub>0.89</sub>Mn<sub>0.11</sub>Te has been measured by the superconducting quantum interference device magnetometer in the temperature range from 5 to 200 K under the applied magnetic field of 1, 2, 4 and 6.5 Tesla, respectively, compared with that of no-magnetic field. The results show that the resistivity increases with increase applied magnetic field at higher temperature from 80 to 200 K, but decreases at lower temperature from 5 to 25 K. There exists a transitive range from 25 to 80 K, where the variation of the resistivity shows different tendencies depending on the strength of magnetic field. Maximum difference of resistivity under 6.5 Tesla from that without magnetic field in the temperature range from 30 to 200 K is only about 5 Ω·cm, but it increases up to 3 orders of magnitude at 5 K. The analysis shows that the variation of resistivity of Hg<sub>0.89</sub>Mn<sub>0.11</sub>Te under the magnetic field is the algebraic sum of the transverse direction magnetoresistance effect and the sp-d exchange interaction effect. TDRME plays major role in the high temperature range. However, with the decrease of temperature, the effect of sp-d EI on the resistivity gradually exceeds that of the transverse direction magnetoresistance effect through the transitive range, and becomes the dominant effect in the temperature range from 5 to 25 K, which leads to the dramatic decrease of resistivity.
基金Funded by the National Natural Science Foundation of China(50336040)
文摘The magnetization of Hg0.89Mn0.11 Te single crystal grown by vertical Bridgman method was studied by using superconducting quantum interference device magnetometer（SQUID Magnetometer）. First, magnetization measurements were done under various magnetic fi eld strengths from-20 kOe to 20 kOe at 5 K, 15 K, and 77 K, respectively. Then, the magnetizations were measured with continuous changes of temperature in the range from 5 K to 300 K under the magnetic field of 0.1 kOe and 10 kOe, respectively. The modifi ed Brillouin function was well fitted with the data of magnetization vs. magnetic field strength. The analysis indicated that there was an antiferromagnetic exchange coupling among Mn^2＋ ions. The results of reciprocal susceptibility vs. temperature fi t Curie-Weiss law very well at the temperatures above 40 K, but deviate from the law from 5 Kto 40 K, which shows that the antiferromagnetic exchange coupling among Mn^2＋ ions increases in the lower temperature range below 40 K. The experimental result was explained by extending higher-order terms in the calculation of susceptibility and fitted by a power law function. The measurements reveal that Hg0.89Mn0.11 Te possesses paramagnetic properties at temperatures from 5 K to 300 K.
基金This work was supported by the Industrial Breed of Shaanxi Provincial Education Committee(Grant Nos.02JC33).
文摘The optical microscope, SEM and EDS were adopted to analyze the rheoforming solidification morpholo-gies and microstructures of deformed AZ91D magnesium alloy after isothermal treatment in semisolid state. The re-sults show that primary α phase can be formed through attachment growth, when the liquid fraction is small; and primary α phase will grow in dendrites, when the liquid fraction is high. Eutectic solidification is carried out in the ways of both dissociated growth and symbiotic growth, de-pending on the morphology of primary α phase. Liquid with eutectic concentration solidifies into lamina eutectic. During solidification of the liquid pools inside grains, α phase can be formed through attachment growth. The eutectic solidifica-tion was mainly carried out in the dissociated pattern.
基金supported by the National Basic Research Program of China (Grant No. 2011CB610401)the Creative Research Group of the National Natural Science Foundation of China (Grant No. 51021063)+1 种基金the National Natural Science Foundation of China (Grant No. 50831007)the Science Center for Phase Diagrams & Materials Design and Manu-facture, Central South University
文摘Knowledge of diffusivity is a prerequisite for understanding many scientific and technological disciplines. In this paper, firstly major experimental methods, which are employed to provide various diffusivity data, are briefly described. Secondly, the fun-damentals of various computational methods, including first-principles method, embedded atomic method/molecular dynamic simulation, semi-empirical approaches, and phenomenological DICTRA technique, are demonstrated. Diffusion models re- cently developed for order/disorder transitions and stoichiometric compounds are also briefly depicted. Thirdly, a newly estab- lished diffusivity database for liquid, fcc_A1, Lie, bcc_A2, bcc_B2, and interrnetallic phases in the multicomponent A1 alloys is presented via a few case studies in binary, ternary and quaternary systems. And the integration of various computational techniques and experimental methods is highlighted. The reliability of this diffusivity database is validated by comparing the calculated and measured concentration profiles, diffusion paths, and Kirkendall shifts in various binary, ternary and quaternary diffusion couples. Next, the established diffusivity databases along with thermodynamic and other thermo-physical properties are utilized to simulate the microstructural evolution for Al alloys during solidification, interdiffusion and precipitation. A spe- cial discussion is presented on the phase-field simulation of interdiffusion microstructures in a series of Ni-Al diffusion couples composed of γ, γ＇, and β phases under the effects of both coherent strain and external compressive force. Future orientations in the establishment of next generation of diffusivity database are finally addressed.
基金supported by the National Instrumentation Program (GrantNo. 2011YQ040082)the National Natural Science Foundation of China(Grant Nos. 50902113,50902114)+3 种基金Program for New Century Excellent Talents in University (Grant No. NCET-10-0076)the National Basic Research Program of China ("973" Project) (Grant No. 2011CB610406)the"111" Project of China (Grant No. B08040)NPU Foundation for Fundamental Research (Grant No. JC20100228)
文摘CdZnTe is an excellent material candidate for high efficiency,high-resolution room-temperature nuclear radiation detectors,and the CdZnTe detectors are being widely used in medicine,industry,safeguard and scientific X-ray and γ-ray imaging and spectroscopic applications.In this work,three CdZnTe planar detectors with different grades,named CZT-1,CZT-2 and CZT-3,respectively,were fabricated.And the effects of mobility,lifetime and de-trapping time on the performance of CdZnTe planar detector,such as the energy resolution,charge collection efficiency and peak to valley ratio,were analyzed.The charge collection efficiency depends on the product of carrier mobility and lifetime,which has a great effect on the energy resolution of detector when the efficiency is less than 90%.The de-trapping time of carriers in deep levels should be responsible for the peak to valley ratio and "polarization".
