Anisotropic plastic deformation behavior of as-extruded ZK60 magnesium alloy at room temperature

The anisotropic plastic deformation behavior of as-extruded ZK60 magnesium alloy at room tempera-ture (RT) was investigated by compressive and tensile testing in different directions, i.e. the loading axis oriented at 0°, 45° and 90° to the extrusion direction. The relationship between texture and plastic deformation behavior were examined. The results show that the extruded ZK60 alloy exhibits a strong ring fiber texture. The mechanical properties are strongly orientation dependent. In tension testing, the 0° specimen exhibited higher yield strength and lower elongation. In compression testing, however, ZK60 alloy exhibited almost the same yield strength in three directions. The anisotropic plastic defor-mation behavior is due to strong fiber texture and the lower symmetry of the hexagonal close packed (hcp) structure of ZK60 alloy. The correlation between texture and mechanical behaviour offers the possibility to improve the mechanical properties of magnesium alloy by optimization of the material production process.     

Microstructure evolution of single crystal copper wires in cold drawing

The deformation microstructure evolution of single crystal copper wires produced by OCC method has been studied with the help of TEM, EBSD and OM. The results show that there are a small number of dendrites and twins in the undeformed single crystal copper wires. However, it is difficult to observe these dendrites in deformed single crystal copper wires. The structure evolution of deformed single crystal copper wires during drawing process can be divided into three stages. When the true strain is lower than 0.94, macroscopic subdivision of grains is not evident, and the microscopic evolution of deformed structure is that the cells are formed and elongated in drawn direction. When the true strain is between 0.94 and 1.96, macroscopic subdivision of grains takes place, and the number of microbands located on {111} and cell blocks is much more than that with the true strain lower than 0.94. When the true strain is larger than 1.96, the macroscopic subdivision of grains becomes more evident than that with the true strain between 0.94 and 1.96, and S-bands structure and lamellar boundaries will be formed. From EBSD analysis, it is found that part of 〈100〉 texture resulting from solidifying is transformed into 〈111〉 and 〈112〉 due to shear deformation, but 〈100〉 texture component is still kept in majority. When the true strain is 0.94, the misorientation angle of dislocation boundaries resulting from deformation is lower than 14°. However, when the true strain arrives at 1.96, the misorientation angle of some boundaries will be greater than 50°, and the peak of misorientation angle distribution produced by texture evolution is located in the range between 25° and 30°. Supported by the National Natural Science Foundation of China (Grant Nos. 50471098 and 59971033), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2003E101), and the Teaching and Research Award Program for Outstanding Young Teachers in Higher Education Institution of MOE, China     

Effect of one-step aging on microstructure and properties of a novel Al-Zn-Mg-Cu-Zr alloy

The effect of one-step aging temper on the mechanical properties, electrical conductivity and the microstructure of a novel Al-7.5Zn-1.6Mg-1.4Cu-0.12Zr alloy has been investigated. The results indicated that with elevating the aging temperature from 100℃ to 160℃, the aging response rate was greatly accelerated, and the UTS at peak aging condition decreased, while the corresponding TYS increased. However, the electrical conductivity of the alloy became higher. After aging for 24 h at 120℃, the peak UTS and TYS values were achieved as 591 MPa and 541 MPa, respectively; but the alloy achieved a lower conductivity, 20.4 MS/m. When T6 temper was performed at 140℃ for 14 h, the UTS decreased only by 1% of the former, whereas the TYS and the electrical conductivity increased obviously, which were up to 559 MPa and 22.6 MS/m, respectively. The major strengthening precipitates of the peak-aged alloy were GP zones and η′ phase. The precipitates in both the matrix and the grain boundary became coarser with rising aging temperature. There were obvious PFZs along the grain boundary both in T6 conditions aged at 140℃ and 160℃.     

Thermal deformation behavior and microstructure of nuclear austenitic stainless steel

Gleeble-1500D thermal simulation tester was employed in the hot-compression investigation of as-cast nuclear 304 austenitic stainless steel under conditions: deformation temperature 950―1200℃; deformations 30% and 50%; deformation rates 0.01 and 0.1 s?1. The results show that the flow stress decreases with temperature rise under the same strain rate and deformation, that the flow stress increases with deformation under the same temperature and strain rate, and that the flow stress increases with strain rate...     

Internal state variable models for microstructure in high temperature deformation of titanium alloys

There exists an interaction between microstructural evolution and deformation behavior in high temperature deformation of titanium alloys. And the microstructure of titanium alloys is very sensitive to the process parameters of plastic deformation process. In this paper, on the basis of plastic deformation mechanism of metals and alloys, a microstructural model including dislocation density rate equation and grain growth rate equation is established with the dislocation density rate being an internal state variable. Applying the model to the high temperature deformation process of Ti60 titanium alloy, the average relative errors of grain sizes between the experiments and the predictions are 9.47% for sampled data, and 13.01% for non-sampled data. Supported by the National Natural Science Foundation of China (Grant No. 50475144), the NPU Foundation for Research (Grant No. NPU-FFR-006), and the National Basic Research Program of China (“973”) (Grant No. G20000672)     

Molecular dynamics simulation of the test of single-walled carbon nanotubes under tensile loading

Molecular dynamics (MD) simulations were performed to do the test of sin-gle-walled carbon nanotubes (SWCNT) under tensile loading with the use of Bren-ner potential to describe the interactions of atoms in SWCNTs. The Young’s modulus and tensile strength for SWCNTs were calculated and the values found are 4.2 TPa and 1.40―1.77 TPa, respectively. During the simulation, it was found that if the SWCNTs are unloaded prior to the maximum stress, the stress-strain curve for unloading process overlaps with the loading one, showing that the SWCNT’s de-formation up to its fracture point is completely elastic. The MD simulation also demonstrates the fracture process for several types of SWCNT and the breaking mechanisms for SWCNTs were analyzed based on the energy and structure be-havior.     

Effect of technological parameters on optical performance of fiber coupler

To find out the influence of technological parameters on optical performance of fused optical fiber device, the fiber coupler was served as subject investigated by using the fused biconical taper machining as experimental setup. Fused fiber coupler＇s optical performances such as insertion loss, excess loss, directivity and uniformity were tested with the optical test system that was constituted of tunable laser and optical spectrum analyzer. Especially the relationship between optical performance and drawing speed was investigated. The experimental results show that the optical performance is closely related to process conditions. At fused temperature of 1 200℃, there exists a drawing speed of 150μm/s, which makes the device＇s performance optimum. Out of this speed region, the optical performance drops quickly. At drawing speed of 200μm/s, the excess loss is relatively small when the fused temperature is above 1 200 ℃. So the technological parameters have close relationship with optical performance of the coupler, and the good performance coupler can＇t get until the drawing speed and fused temperature match accurately.     

Preparation and properties of 4.25Cu-0.75Ni／NiFe2O4 cermet

4.25Cu-0.75Ni/NiFe₂O₄ cermets were prepared by doping NiFe₂O₄ ceramic matrix with the mixed powders of Cu and Ni or Cu-Ni alloy powder as the electrical conducting metallic elements. The effects of technological parameters, such as the adding modes of metallic elements, the ball milling time, the sintering time and the sintering temperature, on the relative density and resistivity of the cermets were studied. The results show that the resistivity of 4.25Cu-0.75Ni/NiFe₂O₄ cermets decreases with increasing temperature, and has a turning point at 590 °C, which is similar to that of NiFe₂O₄ ceramic. The sintering temperature and adding modes of metallic elements have a great influence on the properties of 4.25Cu-0.75Ni/NiFe₂O₄ cermets. When the sintering temperature increases from 1200 °C to 1300 °C, the relative density increases from 89.86% to 95.33%, and the resistivity at 960 °C decreases from 0.11 Ω · cm to 0.03 Ω · cm, respectively. When the metallic elements are added with the mixed powders of Cu and Ni, the cermets of finely and uniformly dispersed metallic phase, high density and electric conductivity are obtained. The relative density and resistivity at 960 °C are 90.23% and 0.04 Ω · cm respectively for the cermet samples sintered at 1200 °C for 2 h, which are both better than those of the cermets prepared under the same technique conditions but with the metallic elements added as 85Cu-15Ni alloy powders. Foundation item: Project (G1999064903) supported by the National Key Fundamental Research and Development Program of China; project(2001AA335013) supported by the National High Technology Research and Development Program of China; project (50204014) supported by the National Natural Science Foundation of China     

锥形管无模拉拔壁厚变化规律

为了确定拉拔速度控制模型,掌握变形规律,制定无模拉拔工艺,研究了无模拉拔成形不锈钢锥形管变形过程中锥形管壁厚变化的影响因素以及壁厚变化的规律.结果表明,锥形管无模拉拔过程中,随着拉拔速度的增大、锥形管长度的延长,锥形管壁厚呈直线规律减小;壁厚变化规律与坯料的原始厚径比以及进料速度、感应加热温度、冷热源距离等工艺参数有关;进料速度越大、感应加热温度越低、冷热源距离越小,无模拉拔后锥形管壁厚越大;原始厚径比为1/6的管坯,当进料速度为20~40 mm min^-1、感应加热温度为900~1100 ℃、冷热源距离为15~40mm时,工艺参数对壁厚的影响因子k为1.02~1.15.     

Processing limit maps for the stable deformation of dieless drawing

Tin bronze wires were produced by dieless drawing. The effects of heating power, the distance between cooler and heater as well as feeding speed on the diameter, the temperature field, and the deformation region profile of the wires were investigated. The results indi-cated that each processing parameter exhibited both lower and upper limits of stable deformation based on the criterion of stable deformation with the diameter fluctuation of ±0.05 mm. Both the temperature and its gradient of the deformation r...     

Plastic deformation of nanocrystalline nickel

A high-resolution electron microscopy study has uncovered the plastic behavior of accommodating large strains in nanocrystalline (NC) Ni subject to cold rolling at liquid nitrogen temperature. The activation of grain-boundary-mediated-plasticity is evidenced in NC-Ni, including twinning and formation of stacking fault via partial dislocation slips from the grain boundary. The formation and storage of 60° full dislocations are observed inside NC-grains. The grain/twin boundaries act as the barriers of dislocation slips, leading to dislocation pile-up, severe lattice distortion, and formation of sub-grain boundary. The vicinity of grain/twin boundary is where defects preferentially accumulate and likely the favorable place for onset of plastic deformation. The present results indicate the heterogeneous and multiple natures of accommodating plastic strains in NC-grains. Supported by the National Nature Science Foundation of China (Grant Nos. 50571000, 10721202) and the National Basic Research Program of China (“973” Program) (Grant No. 2004CB619305)     

Deformation behavior and microstructural evolution of Al-Zn-Cu-Mg-Sc-Zr alloy during high temperature compression

The deformation behavior of a new Al-Zn-Cu-Mg-Sc-Zr alloy was investigated with compression tests in temperature range of 380–470 °C and strain rate range of 0.001–10 s⁻¹ using Gleeble 1500 system, and the associated microstructural evolutions were studied by metallographic microscopy and transmission electron microscopy. The results show that true stress—strain curves exhibit a peak stress, followed by a dynamic flow softening at low strains (ɛ<0.05). The stress decreases with increasing deformation temperature and decreasing strain rate, which can be represented by a Zener-Hollomon exponential equation with the activation energy for deformation of 157.9 kJ/mol. The substructure in the deformed specimens consists of few fine precipitates with equaixed polygonized subgrains in the elongated grains and developed serrations at the grain boundaries. The dynamic flow softening is attributed mainly to dynamic recovery and dynamic recrystallization. Foundation item: Project(2006AA03Z523) supported by the National High-Tech Research and Development Program of China     

Examination of dynamic recrystallization during compression of AZ31 magnesium

This study aimed to investigate dynamic recrystallization (DRX) behavior during compression of magnesium alloy AZ31. Cylinder samples were cut from the extruded rod and hot rolled sheet AZ31 for compression test. The samples were compressed using a Gleeble 1500D at a temperature of 300℃ and a strain rate of 0.01 s-1. Grain orientations and misorientation angles across grain boundaries for the tested samples were obtained by using electron backscatter diffraction (EBSD) technique. The results showed that strong basal texture was observed after 50% compression (ε = 0.69) on both the extruded and hot rolled samples, which have different initial textures. It was observed that with increased strain, DRX grains gradually rotated to basal orientation, and grain boundaries with misorientation angle of near 30° was formed in the samples. At the strain of 0.69, a high fraction of high-angle (> 60°) bounda-ries was present in the extruded sample, whereas almost no high angle boundaries were observed in the hot rolled sheet sample.     

In-flight observations of electromagnetic interferences emitted by satellite

Using the data from STAFF/TC-1, this paper for the first time analyzes the electromagnetic interferences of Chinese scientific satellite. The electromagnetic interference of satellite exists mainly below 30 Hz, but can extend to 190 Hz with an obviously decreasing power spectral density. The electromagnetic interferences at frequencies below 190 Hz have good correlation with the solar aspect angle. The electromagnetic interferences at frequencies between 190 and 830 Hz have also correlation with solar aspect angle. However, the electromagnetic interferences at frequencies above 830 Hz have no correlation with the solar aspect angle. The correlation coefficient between solar aspect angel and electromagnetic interferences is around 0.90. The larger the solar aspect angle, the stronger the satellite electromagnetic interference. When the solar aspect angle increases from 90.6° to 93.6°, the electromagnetic interferences at frequencies <10 Hz increase by 8 times and those at frequencies 190–830 Hz increase by 60%. This close association of electromagnetic interferences with the solar aspect angle indicates that the solar aspect angle is the main factor to determine the electromagnetic interferences. The electromagnetic interferences of satellite in sunlight are larger than those in eclipse. The electromagnetic interference produced by solar panel occupies about 87% in the low frequency band (<100 Hz) and 94% in the high frequency band (>100 Hz) of the total electromagnetic interference produced by satellite. These in flight observations of electromagnetic radiation of satellites will be very helpful to the designs of future satellites of space sciences or earthquake sciences. Supported by the National Hi-Tech Research and Development Program of China (“863” Project) (Grant No. 2008AA12A216), the National Science & Technology Supporting Program during the Eleventh Five-Year Plan, the National Natural Science Foundation of China (Grant No. 40523006), the National Basic Research Program of China (“973” Project) (Grant No. 2006CB806305), and the Specialized Research Fund for State Key Laboratories     

棒材无模拉伸力能参数试验研究

对棒材无模拉伸力能参数进行了试验研究，分析了棒材无模拉伸力能参数的影响因素及影响规律．结果表明：冷热源间距、断面收缩率、变形温度、拉伸速度、冷热源移动速度以及碳素钢材料的含碳量对无模拉伸力能参数都有不同程度的影响．     

Cooling mechanism of embankment with block stone interlayer in Qinghai-Tibet railway

In order to study the cooling mechanism of embankment with block stone interlayer under open and closed conditions,an experimental railway section was built and data within one freeze-thaw cycle were collected. The results explain well the cooling mechanism of embankment with block stone interlayer. Under the open condition in cold seasons,the enforced convection effect occurs within block stone interlayer when the wind speed is large;however,the weak air convection occurs within the block stone interlayer near the bottom of the embankment when the wind speed is slow. Under the open condition in warm seasons,heat conduc-tion occurs within block stone interlayer due to the change in wind speed and di-rection. Under the closed condition,however,the enforced convection within block stone interlayer is so weak that heat conduction is dominant in the whole year be-cause wind is blocked. Therefore,the cooling effect of embankment with a block stone interlayer to the soil beneath it is produced by enforced convection and weak free air convection;both its process and the cooling intensity are controlled by the local wind speed and direction. Because of the difference in the cooling effects,the soil temperature beneath the embankment has a temperature difference of 2℃―4℃ between the open and closed conditions.     

Ultralight X-type lattice sandwich structure (II): Micromechanics modeling and finite element analysis

The methods of homogenization and finite elements are employed to predict the effective elastic constants and stress-strain responses of a new type of lattice structure, the X-structure proposed by the authors in a companion paper. It is shown that in most cases the predictions by the equivalent homogenization theory agree well with the experimental and 3-dimensional finite element calculated results. The theoretical and numerical study supports the argument that the X-structure is superior to the pyramid lattice structure in terms of mechanical strength. Supported by the National Basic Research Program of China (“973” Project) (Grant No. 2006CB601202), the National Natural Science Foundation of China (Grant Nos. 10632060, 10825210), the National “111” Project of China (Grant No. B06024) and the National High-Tech Research and Development Program of China (“863” Project) (Grant No. 2006AA03Z519)     

Numerical study of successive CMEs during November 4–5, 1998

We present the solar-terrestrial transit process of three successive coronal mass ejections (CMEs) of November 4–5, 1998 originating from active region 8375 by using a time-dependent three-dimensional magnetohydrodynamics (MHD) simulation. These CMEs interacted with each other while they were propagating in interplanetary space and finally formed a “complex ejecta”. A newly developed SIP-CESE MHD model was applied to solve MHD equations numerically. The quiet solar wind was started from Parker-like 1D solar wind solution and the magnetic field map was calculated from the solar photospheric magnetic field data. In our simulation, the ejections were initiated using pulse in the real active region 8375. The interplanetary disturbance parameters, such as speed, direction and angular size of the expanding CME, were determined from the SOHO/LASCO data with the cone-model. We discussed the three-dimensional aspects of the propagation, interaction and merging of the three ejections. The simulated interplanetary shocks were compared with the nearby-Earth measurement. The results showed that our simulation could reproduce and explain some of the general features observed by satellite for the “complex ejecta”. Supported by the National Natural Science Foundation of China (Grant Nos. 40536029, 40621003, 40504020 and 40523006), the National Basic Research Program of China (“973”) (Grant No. 2006CB806304), and the CAS International Partnership Program for Creative Research Teams     

Multi-spacecraft observations of ULF waves during the recovery phase of magnetic storm on October 30, 2003

Based on observations obtained by Cluster C1, GOES 10, 12, and Polar, the global ULF wave properties are studied during the recovery phase of a very intense magnetic storm-Halloween storm (October 31, 2003, 21:00–23:00 UT). The results indicate that the ULF waves’ properties observed by different satellites, such as amplitude, period, etc. show large variations. This can be interpreted as that Field Line Resonance (FLR) might take place in the region where Cluster C1 passed. The compressional wave of the cavity mode coupled with FLR’s shear Alfven wave and fed energy to the latter, forming a large-amplitude toroidal mode. From the point of period, Cluster C1 observed the shortest period, GOES 10, 12 observed the middle, while Polar observed the longest. The wave period of toroidal mode observed by Cluster C1 kept almost unchanging when Cluster C1 passed L range from 11.7 to 5.3. Using the Squared Wavelet Coherence analysis method, we estimated that the FLR region in the dayside magnetosphere could expand to at least 4 local time widths. The toroidal mode observed by Polar was a standing wave, while the poloidal mode was a propagating wave, the observation results could be well explained by the waveguide mode theory. Since the solarwind speed V _x was −800 km/s and the dynamic pressure varied little, we speculated that the source of the ULF wave was the Kelvin-Helmholtz instability at the magnetopause triggered by high speed solarwind. Supported by the National Natural Science Foundation of China(Grant Nos. 40425004, 40528005, 40390152) and the National Basic Research Program of China (Grant No. 2006CB806305)     

Statistical values of valence electron structure parameters applied to research on phase transition temperature and eutectoid reaction of titanium alloy

Based on the empirical electron theory of solids and molecules (EET), the statistical values of valence electron structure parameters Sn _A and SE _A which can characterize the properties of alloy phases are calculated, and influences of alloying elements (e.g., V, Nb, Mo, Hf, Zr, Fe, Mn, Co, Cr, Si, and so on) on the phase transition temperature and eutectoid reaction of titanium alloy are discussed with the statistical values of valence electron structure parameters. The research results agree well with real situations. Supported by the National Natural Science Foundation of China (Grant No. 50471022, 50741004) and National Key Basic Research Program of China (“973”) (Grant No. 2007CB613807)