Kehai Li
材料科学技术（英文）
Modification of conventional gas metal arc welding (GMAW) process is of great potential to achieve high productivity with low cost and strong usability. Double-Electrode GMAW (DE-GMAW) is such a modified arc welding process which is formed by adding a bypass torch (gas tungsten arc welding torch) to a conventional GMAW system. The mechanism of metal transfer in DE-GMAW was proposed and verified in this paper. Experiments show that the critical current is decreased so that spray transfer can be obtained at a lower current level in DE-GMAW. Analysis of this significant change in metal transfer phenomena is conducted, and explanation is given out. It is found that the bypass arc in DE-GMAW lifts the anode point on the droplets such that the electromagnetic force becomes larger and squeezes the droplets so that spray transfer can take
place under welding current lower than that in conventional GMAW.
关键词:
Metal transfer
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null
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null
涂学炎
,
王登武
,
陈秀敏
贵金属
doi:10.3969/j.issn.1004-0676.2004.03.004
采用密度泛函理论的广义梯度近似(DFT/GGA),对Run簇(n=2～7)与氧相互作用的几何结构与电子结构及吸附能之间的关系进行讨论.对氧原子及氧分子在Run金属簇上的吸附研究表明:电荷主要是从Ru的5s、4d轨道向O的2p轨道迁移,并使得金属-金属之间的键减弱.比较特殊的是当氧分子在桥位吸附时,Ru与吸附的O2会发生化学反应,并且由于Ru金属轨道的电子向O2的反键πg轨道转移,导致Ru-O之间的键的生成以及O-O之间的键发生断裂.同时,作者也观察到Ru-Ru之间的化学键发生断裂,形成具有原子活性的自由Ru原子,这可以部分解释一旦氧化物种形成,经过一诱导期后,氧化反应会加速进行的实验事实.
关键词:
无机化学
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氧
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钌金属簇
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密度泛函理论
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布居分析
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吸附能
Materials Letters
Highly preferred (002) orientation transparent conductive Al-doped ZnO (ZAO) films were successfully prepared by de magnetron reactive sputtering from a Zn target mixed with Al of 2.0 wt.%. The film has a resistivity of 4.80 X 10(-4) n cm and a visible transmittance of as high as 90%. XPS analysis indicates Al-enrichment on the film surface. The asymmetry of Al 2p(3/2) XPS peak is resolved into two components: one centering at 72.14 eV attributed to metallic Al and the other having a binding energy of 74.17 eV due to oxidized Al. (C) 2001 Elsevier Science B.V. All rights reserved.
关键词:
Al-doped;ZnO;XPS;Al-enrichment;oxide thin-films;optical-properties;electrical-properties;rf;dc;transparent;deposition
WANG Xiao-dong
,
LI Fei
,
JIANG Zheng-yi
钢铁研究学报(英文版)
Non-uniformity of temperature distribution across strip width direction is the ultimate reason why the flatness defect occurs on the strip after cooling process although the strip is flat at the exit of finishing mill. One thermal, microstructural and mechanical coupling analysis model for predicting flatness change of steel strip during the run-out table cooling process was established using ABAQUS finite element software. K Esaka phase transformation kinetics model was employed to calculate the phase transformation, and coupled with temperature calculation using the user subroutine program HETVAL. Elasto-plasticity constitutive equations of steel material, in which conventional elastic and plastic strains, thermal strain, phase transformation strain and transformation induced plastic strain were considered, were derived and programmed in the user subroutine program UMAT. The conclusion that flatness of steel strip will develop to edge wave defect under the functions of the differential thermal and microstructural behaviors across strip width during the run-out table cooling procedure was acquired through the analysis results of this model. Calculation results of this analysis model agree well with the actual measurements and observation.
关键词:
hot rolled strip
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internal stress
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phase transformation
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run-out table cooling
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flatness
王芳
贵金属
doi:10.3969/j.issn.1004-0676.2007.03.012
采用密度泛函理论中的广义梯度近似(DFT/GGA)方法,对Run团簇(n = 9～26)的几何结构与稳定性、团簇表面的Ru与内部Ru间相互作用进行了研究.结果表明:将金属团簇体系放大后,基态稳定结构的原子平均束缚能Eb随着团簇尺寸的增大而增大,当原子数n = 26时,Eb = -6.69eV,与大块金属的Eb(-6.74eV)接近,表明其已接近大块金属的性质;Ru26的平均间距(R)=2.65(A),与理论值2.70(A)和实验值2.704(A)相近;平均配位数CN随着n值的增大而增大,呈现收敛于块体值的趋势.另外,由于大块金属表面的原子不能与足够的原子配位形成饱和的配位结构,所以其上的电子向内层原子转移,使得内层Ru原子呈负电荷,而外层原子呈正电荷,最终导致内层原子之间的相互作用增强而导致键的收缩,外层原子之间键的减弱,从而出现所谓的"驰豫效应".
关键词:
物理化学
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密度泛函
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Ru
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团簇
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结构稳定性
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电子结构
武传松
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张明贤
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李克海
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张裕明
金属学报
doi:10.3321/j.issn:0412-1961.2007.06.021
通过大量的工艺实验,找出了DE-GMAW双焊枪组合的匹配参数,测试了焊接电流波形,拍摄了熔滴过渡图像,并获得了无成型缺陷的焊缝照片.基于实验结果解释了高速焊接工艺的机理.建立了适用于DE-GMAW焊接工艺的有限元模型,并对该工艺条件下的温度场、应力-应变场进行了数值模拟.结果表明:计算出的DE-GMAW焊缝横断面形状尺寸与实验结果吻合良好;在通过焊丝的总电流相同时,DE-GMAW焊接时焊缝尺寸、热影响区宽度、应力、应变及变形均小于常规GMAW焊时的结果.这为DE-GMAW焊接工艺参数优化提供了基础数据.
关键词:
高速电弧焊接
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工艺机理
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DE-GMAW
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有限元分析
ZHANG Xi-liang
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ZHOU Chang-yu
钢铁研究学报(英文版)
The constant embrittlement curve for constant segregation concentration on grain boundary of impurity element P and relationship between equilibrium grain boundary segregation concentration and operation time for 225Cr-1Mo steel were derived based on the theory of equilibrium grain boundary segregation. The mechanism of step-cooling test and mechanism of de-embrittlement for 225Cr-1Mo steel were explained. The segregation rate will increase but equilibrium grain boundary segregation concentration of impurity element P will decrease as temperature increases in the range of temper embrittlement temperature. There is one critical temperature of embrittlement corresponding to each embrittlement degree. When the further heat treating temperature is higher than critical temperature, the heat treating will become a de-embrittlement process; otherwise, it will be an embrittlement process. The critical temperature of embrittlement will shift to the direction of low temperature as further embrittlement. As a result, some stages of step-cooling test would change into a de-embrittlement process. The grain boundary desegregation function of impurity element P was deduced based on the theory of element diffusion, and the theoretical calculation and experimental results show that the further embrittlement or de-embrittlement mechanism can be interpreted qualitatively and quantitatively by combining the theory of equilibrium grain boundary segregation with constant embrittlement curve.
关键词:
step-cooling test
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critical embrittlement temperature
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embrittlement mechanism
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grain boundary desegregation
王玮
,
罗明
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张启富
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赵吉庆
材料保护
为了给核燃料后处理硝酸体系的设备腐蚀控制提供理论参考,对000Cr25Ni20超低碳奥氏体不锈钢在40%硝酸中,沸腾和非沸腾(接近沸腾温度)条件下进行腐蚀试验.结果表明,Cr6+和Run+都能显著促进超低碳Cr-Ni奥氏体不锈钢发生过钝化腐蚀和晶间腐蚀;在沸腾条件下,腐蚀更加严重,Run+加速腐蚀作用更大,在非沸腾务件下,2种离子加速腐蚀作用相差不大.
关键词:
沸腾
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非沸腾
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Cr-Ni奥氏体不锈钢
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过钝化腐蚀
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晶间腐蚀
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硝酸
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Cr6+
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Run+
