共查询到20条相似文献,搜索用时 15 毫秒
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Dongdong Zhao Yi Kong Aijun Wang Liangcai Zhou Senlin Cui Xiaoming Yuan Lijun Zhang Yong Du 《Journal of Phase Equilibria and Diffusion》2011,32(2):128-137
First-principles calculations and semi-empirical equations are employed to determine the self-diffusion mobility of fcc Mg.
All factors entering the vacancy-mediated self-diffusion coefficient, which include the equilibrium lattice parameter, the
enthalpy of vacancy formation and atom migration, and the vibrational entropy of vacancy formation as well as the effective
frequency, are evaluated with the local density approximation (LDA) and generalized gradient approximation (GGA) in first-principles
calculations. These computed quantities are then utilized to calculate the self-diffusion coefficient of fcc Mg. For comparison,
four widely used semi-empirical equations are also used to estimate the self-diffusion coefficient of fcc Mg. The comparisons
show that first-principles calculations and semi-empirical equations yield values close to the activation energy Q for self-diffusion of fcc Mg from the LDA calculation, but the diffusion prefactor D
0 predicted from the four semi-empirical equations are all about one order of magnitude larger than those from the first-principles
calculations. Based on the comparison for the self-diffusion coefficients of fcc Al computed with the first-principles method
and semi-empirical approaches, it is concluded that the self-diffusion coefficient of fcc Mg calculated with the LDA method
is more accurate than the estimation from semi-empirical approaches. 相似文献
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Esin A. Schulz Abhishek Mehta Irina V. Belova Graeme E. Murch Yongho Sohn 《Journal of Phase Equilibria and Diffusion》2018,39(6):862-869
A new formalism recently developed by Belova et al., based on linear response theory combined with the Boltzmann–Matano method, allows determination of tracer and interdiffusion coefficients simultaneously from a single, isotope-free, traditional diffusion couple experiment. An experimental methodology with an analytical approach based on the new formalism has been carried out using the model Cu-Ni system to effectively determine tracer diffusion coefficients from an isotope-free diffusion couple experiment. Cu thin films were deposited in between several binary diffusion couples with varying terminal alloy compositions (Cu-25Ni, Cu-50Ni, Cu-75Ni, Ni). Diffusion couples were annealed at 800, 900 and 1000 °C, and the superimposed concentration profiles of thin film and interdiffusion were analyzed for the simultaneous determination of tracer and interdiffusion coefficients. Processed concentration profiles obtained from the diffusion experiments were also fitted with simple Gaussian distribution function. Results were compared to existing literature data obtained independently by radiotracer experiments, and an excellent agreement has been observed. 相似文献
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Ismail Yildiz Çelik A. Gürhan Gunes Ibrahim 《Protection of Metals and Physical Chemistry of Surfaces》2020,56(5):1015-1022
Protection of Metals and Physical Chemistry of Surfaces - In this study, a mixture of 93% Ni–7% Mg and 97% Ni–3% Mg powders were produced by the TM method and the diffusion kinetics,... 相似文献
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Diffusion along microstructural defects, such as grain boundaries or dislocation pipes, is significantly faster than diffusion through an undisturbed crystal. The ratio of diffusion enhancement is 3-4 orders of magnitude close to the melting point and reaches up to several ten orders of magnitude close to room temperature. An assessment of literature shows a large scatter in the available data and emphasizes the need for representative mean values. Applying a least mean square fit to selected experimental information delivers temperature-dependent functions for the ratio of grain boundary and dislocation pipe to bulk diffusion, respectively. We demonstrate that application of the attained results in a computational framework for the kinetics of precipitation makes the predictive simulation possible for the evolution of particles located at dislocations and grain boundaries. 相似文献
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建立了回转窑实验装置,通过冷态实验研究了回转窑转速、倾角、内径、窑尾挡料圈高度等操作参数和结构参数对物料停留时间的影响。结果表明,物料在回转窑内的停留时间分布近似正态分布;物料停留时间随着回转窑转速、倾角和内径的增大而缩短;窑尾挡料圈高度对物料停留时间影响较复杂,转速小于2.5 r/min时,窑尾挡料圈高度的增加使物料停留时间延长,而当转速大于2.5 r/min时,窑尾挡料圈高度的增加反而使物料停留时间缩短;在某一固定回转窑倾角时,物料停留时间与物料质量流率的乘积与单位转速内物料质量流率近似成线性关系。 相似文献
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Ling Yang M. T. Simnad G. Derge 《JOM Journal of the Minerals, Metals and Materials Society》1956,8(11):1577-1580
Self-diffusion coefficients of iron in molten Fe-C alloys have been measured by using the capillary method. In addition, the samples have been autoradiographed and sectioned to insure that no significant convection has occurred during the diffusion. The results can be represented by the equation D = 4.3×10?3 exp (—12.200/RT) for carbon = 4.6 pct and T = 1513° to 1633°K; and D = 1.0×10?2 exp (—15,700/RT) for carbon = 2.5 pct and T = 1613° to 1673°K. The D values are higher and the heat of activation for diffusion lower in alloys containing more carbon. Calculation based on the Einstein-Stokes equation indicates that the diffusing species is iron ion. 相似文献
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对经过表面扩渗合金化处理的纯Mg试样进行了不同工况条件下的冲刷磨损试验,研究了不同冲刷介质条件中扩渗层的磨损特性.结果表明,纯Mg经表面扩渗处理后,其表面合金层显微硬度(HV)高达166,比基体显微硬度(HV)的73提高1倍以上;扩渗处理后的试样经介质1(油+石英砂)和介质2(水+石英砂)冲刷磨损,结果表明在两种介质条件下,纯Mg扩渗合金化试样的耐腐蚀磨损性能比未处理试样均有不同程度的提高. 相似文献
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《金属学报(英文版)》2017,(10)
In this study, 6061 aluminum alloy and AZ31 B magnesium alloy composite plate was fabricated through explosive welding. Molecular dynamics(MD) simulations were conducted to investigate atomic diffusion behavior at bonding interface in the AI/Mg composite plate. Corresponding experiments were conducted to validate the simulation results. The results show that diffusion coefficient of Mg atom is larger than that of A1 atom and the difference between these two coefficients becomes smaller with increasing collision velocity. The diffusion coefficient was found to depend on collision velocity and angle. It increases linearly with collision velocity when the collision angle is maintained constant at 10° and decreases linearly with collision angle when the collision velocity is maintained constantly at 440 m/s. Based on our MD simulation results and Fick's second law, a mathematical formula to calculate the thickness of diffusion layer was proposed and its validity was verified by relevant experiments. Transmission electron microscopy and energy-dispersive system were also used to investigate the atomic diffusion behavior at the bonding interface in the explosively welded 6061/AZ31B composite plate. The results show that there were obvious Al and Mg atom diffusion at the bonding interface,and the diffusion of magnesium atoms from magnesium alloy plate to aluminum alloy plate occurs much faster than the diffusion of aluminum atoms to the magnesium alloy plate. These findings from the current study can help to optimize the explosive welding process. 相似文献
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镁及其合金是迄今在工程中应用的最轻的金属结构材料,和其他金属相比,镁及其合金有很多突出的工艺及性能特点.例如,其密度小,是所有结构金属中密度最小的一种;在镁中加入不同的金属元素能够形成一系列具有各种性能的合金;熔点低,容易进行热成形,且能耗较低;用作结构件时具有质量轻、比强度高、减震和抗冲击性能好、易切削加工、不易老化;有良好的导热性、无磁、电磁屏蔽能力强、在受到冲击和摩擦时不会产生火花、阳极氧化着色能力强;镁粉在燃烧时可放出耀眼的白光并产生大量的热量;还原性强,可用于提取活性金属等.鉴于这些特点,镁及其合金很早就得到了应用,并且其应用范围由航空航天及军工领域等传统行业逐步发展,走进了千家万户,广泛应用于冶金工业、交通运输领域、3C产品、电化学、医药等行业. 相似文献
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利用现代分析测试手段分别研究了TIG焊直接焊接镁铝和镀锡焊接镁铝的焊缝熔合区形貌,并对其进行了元素扩散行为的分析及比较。结果表明镁铝直接焊接时,镁与铝之间有明显的界面,镁元素向铝母材中进行大量扩散形成扩散层,而铝元素向镁母材中的扩散很少,扩散到铝母材中的镁元素与铝形成Mg17,Al126和β—AlMg金属间化合物,造成扩散层很容易发生断裂。镁铝镀锡焊接,采用熔焊一钎焊连接方法,中间过渡金属锡与母材之间形成了一个成分、组织和性能均不相同的过渡区,该区对接头性能有着较大的影响。锡层对镁铝接头产生拘束强化作用,过渡层比镁铝直接焊接要狭窄,并且尚余一些没有扩散的锡层,阻止了镁元素向铝母材中扩散。锡过渡层对镁与铝的直接接触起到了一定的阻碍作用。 相似文献
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A modified model was proposed to predict the self-diffusion coefficient (D) in the fcc, bcc and hcp structures with the inputs of the lattice parameter and melting point, which are determinable from first-principle calculations and calculation of phase diagram (CALPHAD) method, respectively. The anisotropy of diffusion coefficient in the hcp structure and the distinction of valence in different structures are considered in the present work. As examples, self-diffusion coefficients of Al, Nb, Zn, Au, Ag, Cr, Mo, Ru, Tc and Sn with the fcc, bcc and hcp structures were calculated, and the influencing factors to diffusion coefficient were also discussed. 相似文献
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F. E. JaumotJr. R. L. Smith 《JOM Journal of the Minerals, Metals and Materials Society》1956,8(2):137-142
Self-diffusion in zinc has been used as an instrument for comparison of the absorption and sectioning techniques as a means of studying diffusion. Single crystal as well as poly-crystal samples were used and the temperature range of diffusion extended from 200° to 415°C. For temperatures above 200°C, the data indicate that the results obtained from the absorption technique agree with those obtained from the sectioning technique. The effect on the values of the diffusion coefficient of electroplating vs evaporation as a means of applying the tracer was investigated and no significant difference observed. It was found that an excess or deficiency of tracer did not materially affect the results obtained from the sectioning technique, but invariably caused errors with the absorption technique. 相似文献
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研究了纯镁及表面改性纯镁样品植入动物骨组织后在镁-骨界面处的降解机制以及材料对周围骨组织的影响.选择纯系日本大耳白兔,于股骨处植入样品.术后1、5周后,取出样品制作半薄切片,进行光学显微镜、扫描电镜观察.研究发现,镁棒周围新生类骨组织沉积速度很快,说明镁的腐蚀降解并没有影响骨组织修复过程.结果表明,镁在降解期间安全性较高,有较好的组织相容性. 相似文献
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日本镁合金的应用与研究现状 总被引:2,自引:0,他引:2
综述了日本在汽车、“3C”产品和摩托车上镁合金的应用现状,并通过对1991年至2003年间日本国内申请的镁合金专利技术构成的分析,试图揭示日本镁合金产业的现状、研究动向和发展趋势。另外,还介绍了日本最新的镁合金回收技术。 相似文献