Computational Study of Atomic Mobility in Co-Fe-Ni Ternary Fcc Alloys

The generalized Boltzmann-Matano method has been used to evaluate the interdiffusion coefficients at 1100 °C for the fcc phase of the Co-Fe-Ni ternary system from the concentration profiles developed from single-phase diffusion couple. The evaluated interdiffusion coefficients, together with other experimental data in the literature, have been assessed to develop an atomic mobility database for the fcc phase of the Co-Fe-Ni ternary. The atomic mobility database, in conjunction with the CALPHAD-base thermodynamics, has been used to simulate a number of ternary diffusion couple experiments. Comprehensive comparisons between the calculated and experimental data show that excellent agreement is obtained not only for the general diffusion data of ternary diffusion couple, such as the interdiffusion coefficients and the concentration profiles, but also for much of in-depth diffusion behavior, like the diffusion path, the interdiffusion flux and the shift of the Kirkendall plane.     

Ti-CU固相扩散界面研究

采用“铆钉法”制备了界面为曲面的Ti-Cu扩散偶。用光学显微镜和彩色金相技术,研究了真空保温过程中界面的迁移情况及其影响因素。结果表明,界面迁移受原子扩散控制;温度、保温时间是影响扩散的主要因素。     

Modeling of kinetics of diffusive phase transformation in binary systems with multiple stoichiometric phases

The thermodynamic extremal principle is used for the treatment of the evolution of a binary system under the assumption that all phases in the system are nearly stoichiometric with no sources and sinks for vacancies in the bulk. The interfaces between the individual phases are assumed to act as ideal sources and sinks for vacancies, and to have an infinite mobility. Furthermore, it is assumed that several phases are nucleated in the contact plane of the diffusion couple at the beginning of the computer experiment. Then, it is shown that the number of newly nucleated phases determines the maximum number of polyfurcations (i.e., branching of a single configuration into several distinct configurations) of the initial contact (Kirkendall) plane. The model is demonstrated on a hypothetical binary system with four stoichiometric phases. The inverse problem, namely, the determination of the tracer diffusion coefficients in newly nucleated phases from the thicknesses of new phases and the positions of polyfurcated Kirkendall planes, is treated too. This article was presented at the Multicomponent-Multiphase Diffusion Symposium in Honor of Mysore A. Dayananda, which was held during TMS 2006, the 135th Annual Meeting and Exhibition, March 12–16, 2006, in San Antonio, TX. The symposium was organized by Yongho Sohn of University of Central Florida, Carelyn E. Campbell of National Institute of Standards and Technology, Richard D. Sisson, Jr., of Worcester Polytechnic Institute, and John E. Morral of Ohio State University.     

Assessment and Evaluation of Mobilities for Diffusion in the bcc Cr-V-Fe System

Assessments of diffusion mobility parameters are performed for the bcc Cr-V-Fe alloy system by taking available literature data into account. The main focus is on the diffusion of V in the bcc phase where, in addition to all binaries, ternary interaction parameters are assessed. An experiment is performed in order to study the coarsening of V-rich MC carbide, where the diffusion of V is believed to be of major importance. The measured coarsening rate is compared with the rate calculated using DICTRA, and found to be in satisfactory agreement. The aspects of coarsening experiments as a method to evaluate diffusion mobility data are discussed.     

Study of Diffusion and Marker Movement in fcc Ag-Au Alloys

On the basis of the published CALPHAD-type thermodynamic parameters, the atomic mobilities of Ag and Au in face-centered cubic (fcc) Ag-Au alloys are critically assessed, where self-diffusion coefficients, impurity diffusion coefficients, tracer diffusion coefficients, interdiffusion coefficients and concentration curves are simultaneously optimized. Good agreements are obtained by comprehensive comparisons between the calculated and experimentally measured values. In addition, the developed mobilities are successfully used to study inert marker movement for one-dimensional and two-dimensional cases. It is believed that the obtained parameters can provide helpful guidance for material designs.     

Computational Study of Mobilities and Diffusivities in bcc Ti-Zr and bcc Ti-Mo Alloys

Based on the abundant experimental diffusion data and the thermodynamic parameters in the literature, the atomic mobilities of bcc Ti-Zr and bcc Ti-Mo alloys are critically assessed by means of the CALPHAD technique in this work. Comprehensive comparisons between the calculated and experimentally measured diffusion coefficients are made, where the presently obtained mobility parameters can satisfactorily reproduce most of the experimental data. Moreover, the atomic mobilities derived in the present work are successfully applied to reproduce some measured concentration profiles from diffusion couples in both binary systems and the displacements of Kirkendall makers in the Ti-Mo binary system. It is believed that the proposed atomic mobility parameters contribute to the establishment of a general Ti mobility database, which is useful in designing novel high-temperature Ti alloys.     

VisiMat-Software for the Visualization of Multicomponent Diffusion in Two and Three Dimensions

VisiMat is a MATLAB code with a graphical user interface (GUI) that is intended to be used for instructional purposes. It is designed to facilitate understanding of the complex multicomponent diffusion phenomena that may occur in couples of three or more components with a special emphasis on the compositions and locations where maxima, minima, or zero-flux behavior may occur. VisiMat is an implementation of the square-root diffusivity method for predicting and visualizing the diffusion behavior of ternary and quaternary, single-phase, multicomponent diffusion couples with constant diffusivity. The program determines concentration profiles, fluxes including zero-flux conditions, and two- or three-dimensional representations of composition space and diffusion path. Although the code will accomodate any number of components, the three-dimensional visualizations are not possible for more than four components.     

失稳分解组织演化和粗化动力学的晶体相场法研究(英文)EI北大核心CSCD

以二元对称与非对称合金的调幅分解为研究对象,采用晶体相场模型从沉淀相演化和粗化机制两方面分析合金的失稳分解。研究表明,当合金的成分由对称点向非对称点转变时,沉淀相形貌逐渐由长条形过渡为球形;后期粗化机制由邻近颗粒的合并机制转变为Ostwald熟化机制;只有当二元合金的成分接近于失稳线时,其粗化动力学才较好地与修正的LSW理论符合。     

Al-Zn-Mg-Cu合金第二相粒子及其无析出区与晶界的作用过程研究

制备一种含Sc和一种含Cr、Mn、Ti、Zr的Al-Zn-Mg-Cu合金,采用透射电镜研究合金中第二相粒子周围的无析出微区和晶界上的无沉淀析出带及其相互的作用过程,给出单个第二相粒子对晶界作用力的方程.当驱使晶界迁移的动力大于粒子及其周围的无析出微区对晶界的阻碍作用时,晶界被粒子穿透而形成孔洞.在晶界扫过粒子的过程中,经历了先加速后减速两个阶段.晶界位于粒子直径区位置时所受的阻力最小、运动速度最大.当晶界能与相界能增量之和等于晶界运动的驱动力时,晶界被粒子钉扎而停止运动.在晶界迁移的过程中,溶质原子倾向于由高浓度区域向低浓度区域扩散,晶界和粒子周围的无析出区对晶界的迁移过程有明显的影响.     

石墨化碳黑球固相萃取富集-火焰原子吸收分光光度法测定金的研究

研究了用石墨化碳黑球固相萃取富集,火焰原子吸收分光光度法测定Au的方法.含Au样品用微波消化,消化后样品溶液中的Au(III)用载有TBP(磷酸三丁酯)的石墨化碳黑球固相萃取富集,用亚硫酸钠溶液反方向洗脱小柱上富集的Au(III),然后再用原子吸收测定,Au(III)含量在0～3.5μg/mL符合比耳定律,方法的相对标准偏差为2.6%～3.0%,标准回收率92%～95%.方法用于环境水样中Au(III)的测定,结果令人满意.     

同时考虑界面非等温特性和对流影响的二元合金自由枝晶生长模型

在同时考虑界面非等温性质以及强制对流影响的情况下,提出二元合金的扩展自由枝晶生长模型.模型对比表明:由于溶质扩散系数通常比热扩散系数小3个数量级,当低过冷时,对流对溶质扩散的影响比其对热扩散的影响更强烈.当高过冷时,对流对枝晶生长的影响很小.此外,本模型能够对现有Cu70Ni30合金实验数据给出一致的描述,特别是在低过...     

一种微合金化0Cr13Ni4Mo不锈钢的相图及临界转变温度研究

用热力学计算结合示差量热分析(DSC)方法研究了一种水轮机叶片用V、N微合金化CrNiMo不锈钢的相图及临界转变温度,获得了该钢的伪二元平衡相图、平衡条件下各相的摩尔分数与温度的关系曲线。该钢的Ac1和Ac3温度分别为580℃和730℃,VN的析出温度为1 010℃。     

Computational study and experimental comparison of the in-flight particle behavior for an external injection plasma spray process

A three-dimensional computational fluid dynamic (CFD) analysis using Fluent V5.4 was conducted on the in-flight particle behavior during the plasma spraying process with external injection. The spray process was modeled as a steady jet issuing from the torch nozzle via the heating of the are gas by an electric are within the nozzle. The stochastic discrete model was used for the particle distribution. The particle temperature, velocity, and size inside the plasma plume at a specified standoff distance have been investigated. The results show that carrier gas flow rate variation from 2 standard liters per minute (slm) to 4.0 slm can increase the centerline particle mean temperature and mean velocity by 10% and 16%, respectively, at the specified standoff distance. A further increase of the carrier gas flow rate to 6 slm did not change the particle temperature, but the particle velocity was decreased by 20%. It was also found that an increase in the total arc gas flow rate from 52 slm to 61 slm, with all other process parameters unchanged, resulted in a 17% higher particle velocity, but 6% lower particle temperature. Some of these computational findings were experimentally confirmed by Kucuk et al. For a given process parameter setting, the kinetic and thermal energy extracted by the particles reached a maximum for carrier gas flow rate of about 3.5–4.0 slm.     

Preparation for intermetallic powders of Cu-Sn and Cu-Ni-Sn systems via solid-liquid reaction milling technique

The Cu-Sn binary intermetallic powders were obtained via a patented reaction ball milling technique. The Sn melt reacted with the solid-state Cu during the milling process at different temperatures for different intervals. Two kinds of binary intermetallics were obtained. For 12 h, Cu6Sn5 was prepared by milling Sn melt at 573 K while Cu3Sn by milling Sn melt at 773 K. And a mixture of Cu6Sn5 and Cu3Sn was fabricated at 673 K. All these intermetallic powders had mean grain sizes of less than 100 nm. A finer microstructure was obtained by milling Sn melt blended with 20%（mass fraction） Ni powders at 573 K for 12 h. The reaction mechanism and advantages were discussed in comparison with that of high-energy ball milling. The results show the solutionizing of Ni powders in the Cu6Sn5 intermetallic.     

逆向工程中的CAD建模技术及软件系统

三维CAD模型的重建是逆向工程中的关键技术,而伴随着逆向工程及其CAD重建相关技术理论研究的深入进行,也涌现出大量的商业化逆向工程CAD建模软件系统.本文对目前逆向工程CAD建模及软件技术进行了分析和总结,给出了利用逆向工程软件进行CAD建模的实例,并展望了逆向CAD及软件技术的发展方向.     

Al、Zn对Mg-Li相界合金化效应的第一性原理研究

采用基于密度泛函理论(DFT)的第一性原理超软赝势平面波方法,研究了Al、Zn对Mg-Li合金中α-Mg/β-Li相界断裂强度的影响。体系结合能的计算结果表明Al、Zn固溶于Mg-Li合金后其结构更为稳定;从所得断裂功、态密度以及电荷密度的结果来看,Al更容易固溶于α-Mg固溶体中,对断裂强度的增强作用优于占位于α-Mg/β-Li相界面;Zn占位于α、β晶内、相界面的倾向性不明显,但均可使体系的断裂强度提高;Al、Zn复合合金化后使体系稳定性得到提高,断裂强度等得到进一步的改善。环境敏感镶嵌能的计算结果表明Zn比Al更容易偏聚于相界面;Al、Zn合金化对体系稳定性、断裂强度产生的影响主要是由于Al-3s3p轨道电子、Zn 3d轨道电子贡献产生了新的成键峰,以及Mg 2p轨道及Li 2s轨道电子在费米能级处共同作用的结果。     

Phase field model for the dynamics of steps and islands on crystal surfaces

Surface stress and lattice strain are the essential factors on the self-organization of a surface, because they affect remarkably adatom diffusion on surfaces and at step edges and induce the elastic interaction between the surface steps. In spite of the importance, their kinetic role on the growth dynamics of the step and the islands in thin film deposition is not yet fully understood. Therefore, in this work, a continuum model is presented, which considers both elastic and entropic interactions between the steps or the islands on the crystal surface and growth dynamics of the steps or the islands. The present model is based on the Ginzburg-Landau approach on phase transition and reduces to the Gibbs-Thompson equation at the step edges. In addition, the elastic field, which is generated by the surface force, is calculated using elastic surface Green function under the assumption that the atomic displacement field decays exponentially from the surface. Using the resulting atomic displacement, the elastic interaction between the surface steps is incorporated into the model. Through numerical simulations, it is shown that the elastic interaction between the steps in our model is in good agreement with previcus theories and that the phase field model has the ability to solve the various phenomena of the step dynamics.