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Homogeneous Plastic Flow of Fully Amorphous and Partially Crystallized Zr41.2Ti13.8Cu12.5Ni10Be22.5 Bulk Metallic glass

Q.WANG , J.J.Bl , in , M.Suery , B.Van de Moortele , J.M.Pelletier

材料科学技术(英文)

The homogeneous plastic flow of fully amorphous and partially crystallized Zr41.2Ti13.8Cu12.5Ni10Be22.5 bulk metallic glass (Vit1) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory. Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystallized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amorphous alloy. Thus, it is proposed that the flow behavior of the nanocrystalline/amorphous composite at 646 K is mainly controlled by the viscous flow of the remaining supercooled liquid.

关键词: Homogeneous plastic flow , null

Mechanism of Metal Transfer in DE-GMAW

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 , null , null

Van der Waals interactions between two parallel infinitely long single-walled nanotubes

Chemical Physics Letters

The potential energies of van der Waals (VDW) interactions between two parallel, infinitely long and perfect SWNTs with identical, and different sizes were studied based on the continuum Lennard-Jones model. The conclusion of Girifalco's work on (n, n) SWNTs that the potentials of SWNT-SWNT fell on a single curve, is also applicable to SWNTs with different sizes. We further obtained the corresponding constants of the well depth \phi(0)\ and equilibrium VDW gap g(0) for SWNTs with a radius from 2 to 25 Angstrom. (C) 2005 Elsevier B.V. All rights reserved.

关键词: carbon nanotubes;graphite;bundles;c-60;moduli;ropes

Simple approach to estimating the van der Waals interaction between carbon nanotubes

Physical Review B

The van der Waals (vdW) interactions between carbon nanotubes (CNTs) were studied based on the continuum Lennard-Jones model. It was found that all the vdW potentials between two arbitrary CNTs fall on the same curve when plotted in terms of certain reduced parameters, the well depth, and the equilibrium vdW gap. Based on this observation, an approximate approach is developed to obtain the vdW potential between two CNTs without time-consuming computations. The vdW potential estimated by this approach is close to that obtained from complex integrations. Therefore, the developed approach can greatly simplify the calculation of vdW interactions between CNTs.

关键词: molecules;clusters;bundles;growth;phase;c-60

Properties of ZnO : Al films on polyester produced by de magnetron reactive sputtering

Materials Letters

High preferred (002) orientation Al-doped ZnO (ZAO) films have been prepared by de magnetron reactive sputtering of an alloy target (98.5 wt.% Zn-1.5 wt.% Al) onto polyester substrates. The structural, mechanical, electrical and optical properties were investigated. The ZAO film has a sheet resistance of as low as 47.5 Omega/square and an average visible transmittance of about 70%. An average IR reflectance of about 70% in the region of 2.5-25 mum also has been obtained. (C) 2001 Elsevier Science B.V. All rights reserved.

关键词: Al-doped ZnO (ZAO);polyester;mechanical;IR reflectance;thin-films;optical-properties;oxide-films;electrical-properties;rf;temperature;orientation;parameters;deposition;substrate

Formation of Al-doped ZnO films by de magnetron reactive sputtering

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

Purification of multiwalled carbon nanotubes by annealing and extraction based on the difference in van der Waals potential

Journal of Physical Chemistry B

The potential energies of van der Waals interactions between two multiwalled carbon nanotubes (MWNTs) as well as two carbon nanoparticles (CNPs) were calculated and compared on the basis of the continuum Lennard-Jones model. The well depth of the potential is 1 order of magnitude higher for MWNTs than for CNPs, indicating that MWNTs and CNPs can be separated from each other through polymer-induced steric stabilization. On the basis of this prediction, a novel method for the purification of MWNTs was proposed. The method involves a high-temperature annealing ( 2600 degrees C, 1 h) followed by an extraction treatment with a selected dispersing agent. While the annealing process evaporates the metal particles, the extraction treatment removes CNPs. The quality of the nanotubes obtained after purification was examined by laser Raman, thermogravimetric analysis, and electron microscopy observations.

关键词: decomposition;hydrocarbons;temperature;nanofibers;pyrolysis;monoxide;bundles;purity;gas

DE-GMAW高速电弧焊工艺机理的研究

武传松 , 张明贤 , 李克海 , 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 , 工艺机理 , DE-GMAW , 有限元分析

Mechanism of Embrittlement and De-Embrittlement for 225Cr-1Mo Steel

ZHANG Xi-liang , 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 225Cr-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 225Cr-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 , critical embrittlement temperature , embrittlement mechanism , grain boundary desegregation

DE-GMAW高速电弧焊工艺机理的研究

武传松 , 张明贤

金属学报

根据当前制造业对高效、优质、低耗焊接技术的迫切要求,研发出低成本的高速电弧焊接新工艺DE-GMAW。该工艺在常规GMAW焊接设备的基础上,通过附加GTAW焊枪构成旁路电弧,分流了一部分通过焊丝的焊接电流,在施加于焊丝的电流较大的情况下(保证了熔敷率),减小了作用于母材的热输入,解决了高速焊接面临的矛盾,实现了高速电弧焊接。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和应力变形进行了数值模拟。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 , process mechanism , DE-GMAW , finite-element analysis

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