GTAW多相流数值模拟的相界面实时标记方法

在大电流GTAW的非稳态多相流数值模拟中,需要将电弧热与电弧压力加载在金属相与气相之间的动态变化的界面上,以便准确描述电弧与熔池之间的相互作用.因此提出了一种相界面实时标记方法,通过在三维计算域网格数据中遍历搜索相体积分数梯度的最大值,识别出临近相界面的单层网格区域并施加标记,将面热源与表面力除以网格厚度转化为体热源与...     

A method for computing diffusion coefficients in multiphase systems

Amethod for computing the effective values of diffusion coefficients in phases on the basis of a mathematical model of the process of diffusion saturation in multiphase systems is suggested. Diffusion coefficients are determined with the use of the results of solution of a direct diffusion problem. Regular features of the influence of diffusion coefficients on the thickness of phases in the diffusion zone are established.     

Morphology and reaction kinetics of the interface formed by diffusion bonding

采用固相真空扩散连接方法, 在873-913 K保温40-240 min条件下对轧制厚度分别为 20和60 um的Mo和Al箔进行扩散连接. 发现Mo-Al固-固界面反应初生相在Mo箔内部形核进而“破壳”生长的形貌演变模式, 成分分析表明该初生相为Al8Mo3. 初生相“破壳”后,Mo-Al界面上由Mo至Al的产物分布依次是Al8Mo3, Al5Mo和Al12Mo;在913 K保温240 min后, Al8Mo3与Al5Mo间出现Al4Mo相. 界面反应的动力学分析表明, 873-913 K条件下, Mo-Al界面反应初生相孕育期为 52-34.5 min; Al原子在Mo-Al界面新生相内和Mo箔内的扩散指前因子D01和D02分别为4.61 10-2和2.05 10-2 cm2/min, 扩散激活能G Al-1和G Al-2分别为0.98和1.48 eV.     

等离子多层熔积混相瞬态流场与温度场的模拟

建立了一种二维等离子熔积成形瞬态模型,该模型描述了熔积成形过程中多层熔积层的自由表面发展,并模拟了熔池内流体流动和传热.通过水平集(Level-Set)方法处理熔积轨迹、液/气界面等因素,考虑了熔体流动的主要驱动力-表面张力梯度、表面曲率以及浮力等.并采用SIMPLEC算法求解控制方程.以K163合金为例,对多层熔积成形过程混相瞬态场进行了模拟,所得到的计算结果与试验结果基本一致;并分析了熔积工艺参数(熔积电流、熔积扫描速度和送粉速度)对熔积层表面形貌及熔积质量的作用规律.     

Thermodynamically consistent phase field approach to phase transformations with interface stresses

Thermodynamically consistent phase field theory for multivariant martensitic transformations is developed with the main focus on introducing correct interface stresses (tension). The nontrivial point is that the interface tension (physical phenomenon) is introduced with the help of some geometric nonlinearities, even when strains are infinitesimal. Total stress at the diffuse interface consists of elastic and dissipative parts which are determined by the solution of the coupled system of phase field and viscoelasticity equations and the introduced interface stresses. An explicit expression for the free energy is derived that results in the desired expression for the interface stresses consistent with the sharp interface for the propagating nonequilibrium interface. Analytical expressions for nonequilibrium interface energy, width, entropy excess, as well as distribution of the interface tension are derived and parametrically studied. Interface stress tensor distribution is also obtained and analyzed for a critical martensitic nucleus. The possibility of extending the developed approach to other phenomena and more general models is discussed.     

Growth kinetics of oxide films at the polyaniline/mild steel interface

The growth rate of oxide film formed at the polyaniline/mild steel interface was investigated by open circuit potential (OCP) measurements. The OCP of polyaniline base (EB) coated electrode displayed three feature changes during immersion: t₁ ? t₂, t₂ ? t₃ and >t₃, and the oxide film grew mainly in t₂ ? t₃ time range. The oxide film growth followed a direct logarithm law, the growth rate decreased with increasing NaCl concentration and temperature. With increasing pH, the growth rate decreased first and then increased. The apparent activation energy of oxide film growth was calculated as ?39.8 kJ/mol, indicates that oxide film growth was under diffusion control.     

三元合金中界面迁移率的相场法计算(英文)

基于定量相场模型,提出一种新方法来计算界面迁移率,并将该方法应用于 Ti-6Al-4V 合金的α/β界面。相场模拟表明,更高的界面迁移率将导致更快的相转变速率,但在扩散控制的条件下,只有唯一的界面迁移率能匹配扩散方程。通过比较采用相场模拟和经典扩散方程所得到的相变动力学,可以得到不同温度下的界面迁移率。结果表明,计算所得的界面迁移率随着温度的升高而增加,且与 Arrhenius 方程吻合得很好。     

Analysis of mechanical property distribution in multiphase ultra-fine-grained steels by nanoindentation

The strength characteristics of microphases in ultra-fine-grained steels were analyzed using nanoindentation and AFM. It was found that there were fine ferrite grains (1–2 μm) formed by a strain-induced dynamic transformation in ultra-fine-grained steels. They had equiaxed and polygonal grain shape, and higher hardness and elastic modulus than coarse ferrite transformed statically. Strengthening factors of strain-induced dynamic transformation ferrite were analyzed in terms of cementite particles and dislocation density.     

Near field inversion method to measure the material properties of a layer

This study develops an in situ methodology that uses ultrasonic waves to measure the material properties of a layer. These material properties include the longitudinal and shear wave speeds, as well as the thickness of the layer. The unknown properties are determined by comparing measured experimental data with values obtained from a theoretical model. Emphasis is placed on the effectiveness of measuring both the in-plane, and the out-of-plane surface displacement components with a laser Doppler vibrometer. An inversion scheme compares (in the frequency domain) the experimentally measured data with data predicted using the theoretical model, and an error-function quantifies the difference between these values. Finally, a downhill-simplex algorithm is used to minimize this error-function and thus determine an optimum set of material properties.     

Synthetic approach to alloy thermodynamics and kinetics by cluster variation method and path probability method

The cluster variation method of equilibrium thermodynamics is employed to calculate the Ll₀-disorder phase diagram. The stability analysis based on the second-order derivative of the free energy functional with respect to the deviation of correlation functions from their equilibrium values yields the 100 instability locus in the phase diagram. The time evolution of cluster probabilities at the phase transition is investigated on the basis of the path probability method of non-equilibrium statistical mechanics. Thereby the synthetic study of thermodynamics and kinetics based on the cluster variation method and the path probability method is attempted. It is shown that the fluctuation is necessary to drive the ordering reaction above the instability temperature, whereas the spinodal-like ordering transition takes place below the instability temperature. The extension of the present study of a spin system to an alloy system is briefly discussed and a critical problem to be settled is pointed out.     

Bonding interface between TiAl intermetallic compound and Ti under the electric field

TiAl intermetallic compound was synthesized and bonded together with Ti substrate synchronously by using fieldactivated and pressure-assisted synthesis (FAPAS) process.The effect of electric field on t...     

Design method of electromagnetic field applied to Al-alloy electromagnetic casting

The electromagnetic pump imposes the electromagnetic motive force （Lorentz force） on the liquid metal directly and makes it move along the definite direction by using the function of electric current and magnetic field in the conducting fluid. Compared with the traditional die casting, the system of counter-gravity casting can effectively control the speed of filling to make Al-alloy liquid fill steadily by adjusting controlled-current. So the foundry defects can be decreased or avoided effectively by this system. Based on the theory of electromagnetic pump, the design method of electromagnetic field in electromagnetic pump was investigated emphatically. The rule of magnetic induction intensity B influenced by the divided electromagnet airgap＇s size was founded. Furthermore, the empirical formula of magnetic induction intensity B in a magnetic airgap for an open magnet in the saturated state was deduced by mathematics regression analysis. Counter-gravity casting applied to the Al-alloy electromagnetic filling was developed with this method. Besides, the electromagnetism filling counter-gravity casting process of the turbo-charge blade wheel was also fixed. The eligibility rate of blade wheel produced by such technique can be increased to 98%. The casts have compact structure and excellent capability.     

Effect of interface properties on the kinetics of the hydrogen electrode reaction II: The anodic region

The galvanostatic desorption of hydrogen held in Pd-Ag electrodes in aqueous solutions with and without thiourea was studied.

The effect of adsorption of poison molecules on the Volmer reaction and on the transfer process of hydrogen from the bulk to the permeation surface is reported.

The experimental results obtained indicate that the chemisorption of thiourea causes a sharp decrease in the kinetic parameters of both steps involved in the overall oxidation process.     

Effect of the interface properties on the kinetics of the hydrogen electrode reaction I: The cathodic region

The effect of thiourea adsorption on the kinetics of the hydrogen electrode reaction was studied for Pd-Ag membranes polarized cathodically in aqueous sulphuric acid.

The equilibrium relationship between the amount of hydrogen in the electrode and its open-circuit potential was established in order to interpret the kinetic data.

The influence of thiourea adsorption on the rates of the elementary steps involved in the overall process was examined and the results were interpreted in terms of interactions between metal and sulphur atoms.     

Behavior of particles in front of metallic solid/liquid interface in electromagnetic field

1　INTRODUCTIONTheinteractionbetweentheparticlesandtheso lidifyinginterfaceisofteninvolvedintheprocessingofmetallicmaterials .Forexample ,duringthesolidi ficationofthemetalcasting ,theinclusioninthemoltenmetal(includingforeigninclusionandsec ondaryinclusion)ispossibletobeengulfedbysolidi fyinginterfacetostayinthecasting ,alsoitispossibletobepushedbytheinterfacetoretaininthemoltenmetal.Anothercaseis ,thereinforcingparticleswillbeengulfedtoenterthesolidandpossiblypushedbytheinterface ,whichw…     

数码开关占用的输入点的借用方法

0 前言 对使用可编程序控制器控制的机床,如要改进机床的性能,需要为数不多的输入点,在无备用输入点情况下,可以考虑对已经安排的输入点的重新分配,借助软件编程,空出实际上并无功能的输入点以作它用.     

行波磁场对定向凝固Sn-Cd合金界面形貌的影响

对直径为4 mm的Sn?0.65%Cd合金在行波磁场中进行定向凝固,结果发现其界面形貌是丰富多样的。在向上的行波磁场上,随着磁场强度的增大(B≤10.3 mT),平界面和胞状界面交替转变。当加载向下的弱强度的行波磁场(B=3.2 mT)时,界面形貌由浅胞状向深胞状转变。当磁场强度进一步增大时,界面两侧呈现微弱的不一致,但是在强的磁场下界面形貌大致趋向于平界面(B≤10.3 mT)。这种界面的不稳定性可能归因于行波磁场驱动的流动。另外,在向上的行波磁场中界面形状几乎是水平的,但是在向下的行波磁场中界面形状是倾斜的。     

电磁场对金属凝固界面前沿颗粒行为及分布的影响

探讨了电磁场耦合定向凝固过程中非金属颗粒在金属中的分布与电磁力的定量关系．从理论上指出,控制电磁力周期及凝固参数可制备出颗粒浓度与金属生长距离呈函数关系的新型复合材料．采用过共晶Al-19％Si合金的定向凝固实验结果表明,通过周期性地施加电磁力,合金中的初晶富Si颗粒呈层状分布,表面硬度也呈周期变化．通过改变电磁力施加周期和凝固速率,可以自由改变富Si层之间的宽度．