扩散温度对TC4合金表面Cu/Ni复合镀层结构及腐蚀性能的影响

论文采用扩散热处理研究了Cu/Ni/Ti复合镀层不同温度下的扩散行为,分析了扩散层结构,并讨论了扩散过程对镀层结构及腐蚀性能的影响。结果表明：由于Cu/Ni/Ti原子之间的互扩散,形成稳定的扩散层,可以有效提高镀层表面耐蚀性能;随着热扩散温度上升到700℃,膜层结构致密,在扩散层中形成了NixTiy金属间化合物及少量的CuxTiy金属间化合物,镀层表面的耐蚀性最好;温度升高到800℃时,在膜层界面处引发了Kirkendall效应,所形成的Kirkendall空位相互聚集长大,形成裂纹或孔洞,使得镀层疏松多孔,从而低了耐蚀性。     

Cu/Ni固相扩散界面的研究

采用彩色金相技术对“嵌入式”Cu/Ni扩散偶真空扩散处理时的界面迁移现象进行了观测,并研究了Cu/Ni界面间的扩散行为。结果表明,扩散偶在退火温度1123~1223K、保温时间25~150h(0·9×105~5·4×105s)的工艺条件下反应,Cu/Ni界面间结构由α/β转变为α/α′/β,其中α′为扩散层,实质是成分不均匀的固溶体,Cu/Ni界面间扩散行为是Kirkendall效应的一种显现,即界面上Cu和Ni元素均发生了扩散,但主要是Cu原子向Ni层的扩散。最后在试验数据基础上发现,扩散层厚度L与退火时间t之间满足抛物线L=K(t/t)n关系。     

Kirkendall效应和空心纳米晶体的人工合成

在1946年被发现的Kirkendall效应,对科学技术引起很大的冲击,至今,仍在许多科学技术和工程领域受到关注。本文悦目瞭然地阐述Kirkendall效应和Darken分析,计算实例,空位风和反Kirkendall效应。最后,更为重要地指明,2004年发表的应用纳米尺度Kirkendall效应人工合成中空纳米球方法提供了人工合成无机化合物的空心纳米晶体和纳米管的通用途径。近年来,这种具有空心结构的纳米晶体愈来愈受到人们的青睐。     

强磁场下Ni-Cu系原子的扩散行为

采用Cu/Ni/Cu扩散偶研究强磁场对Ni?Cu系原子扩散行为的影响。发现该扩散偶在有、无强磁场条件下退火处理时,Ni?Cu 系原子互扩散过程中的互扩散系数随着互扩散区内 Ni 原子摩尔分数的增加而增加,并且在强磁场条件下退火处理后,所有的互扩散系数均小于相应条件下无磁场处理时的互扩散系数。表明强磁场的施加延迟了Ni?Cu系原子的互扩散行为。分析指出,上述强磁场对原子扩散的延迟行为是通过降低互扩散过程中的频率因子而不是互扩散激活能来实现的。     

Ti-Zr二元体系BCC相扩散移动性的评估

在丰富实验数据的基础上,结合相关的热力学参数,评估并获得Ti-Zr二元体系BCC相中的扩散移动性数据库.通过扩散移动性数据库计算的扩散系数与实验数据取得很好的一致性.基于Calphad技术,在所获得的扩散移动性数据库的基础上,结合相关的热力学描述,成功地模拟Ti-Zr二元体系半无限扩散偶浓度曲线和Kirkendall面的移动,并计算点阵面的移动距离.     

Ir／Mo互扩散研究

研究了Ir/Re喷管制备过程中的Ir/Mo互扩散问题。在电子探针测量的基础上,根据扩散理论和Ir-Mo相图数据,建立并推导Ir/Mo扩散模型和解。计算得到Ir3Mo相中的互扩散系数为:D=9.0×10-9exp(-1.46eV/kT)(cm2/s),Ir基固溶体中的互扩散系数为:D=5.0×10-10exp(-1.1eV/kT)(cm2/s)。确定喷管中Ir/Mo互扩散的特点,给出估算Ir3Mo相层厚的方法。确定Re在Ir3Mo相中的扩散主要是受Ir控制。     

金属扩散系数的测量方法与理论研究

介绍了金属扩散系数的几种测量方法,包括扩散对法、毛细管-熔池法、剪切单元法、转盘法和等离子轰击技术等;以及几种自扩散系数的理论研究和液态合金的扩散、自扩散系数的理论研究方法,包括硬球模型、线性轨道假说、小步扩散理论、流体动力学模型、经验公式及慢中子散射技术,液态合金中的扩散有Darken给出的互扩散系数及互扩散系数模型。通过对比各种实验方法的优缺点,分析实验值与理论计算值之间出现偏离的原因,指出了寻求有效的示踪原子是今后的研究动向,探索离子轰击能够促进扩散的原因将成为今后的研究重点。     

金刚石与钛的原子热压扩散行为的分子动力学模拟

应用分子动力学方法模拟了金刚石与钛在热压扩散过程中的原子扩散行为,模拟了不同扩散温度下金刚石与钛界面的原子扩散过程,得到了界面的原子浓度分布、扩散速度以及模拟扩散系数值;采用热压扩散法在金刚石表面镀覆钛层并测量界面的扩散带宽度。研究结果表明：在热压扩散过程中C原子的扩散速度大于Ti原子;随着扩散温度的升高,原子存在低速和快速两个扩散阶段。通过热压扩散的分子动力学模拟对模拟的扩散系数进行数据拟合,能够确定C和Ti原子的扩散因子和扩散激活能,从而简单、有效地确定原子的扩散系数计算公式。金刚石与钛扩散带宽度的计算值与实测值相近,应用分子动力学方法获得的原子扩散系数公式是可行的。     

Ir／Re互扩散研究

在电子探针测量的基础上,根据扩散理论和Ir-Re相图数据,建立了一个全新的Ir/Re两相扩散模型。计算得到在1200℃~2000℃时Ir基固溶体中的互扩散系数为:D=1.17×10-6exp(–1.80eV/kT)(cm2/s),Re基固溶体中的互扩散系数为:D=1.36×10-8exp(–1.21eV/kT)(cm2/s)。确定喷管中Ir/Re为晶界扩散。     

铜/锡界面间扩散行为分子动力学模拟

采用分子动力学方法,基于MEAM原子间作用势模型模拟了钎焊过程中固液界面扩散过程,从原子尺度对液态钎料原子向母材金属中的扩散行为进行模拟计算.计算了锡钎料在510 K温度下向母材中的扩散系数.结果表明,当扩散反应达到平衡态时,原子位移平均平方代换与反应时间成线性关系,钎料原子在x与y矢量方向扩散速度相近,且远大于z方向扩散速率.根据爱因斯坦扩散方程计算得到界面反应过程中钎料原子在xyz三个矢量方向上的扩散系数分别为2.03×10-9,2.05×10-9,5.06×10-10 cm2/s.z方向扩散系数模拟值同试验值比较,模拟结果与试验结果吻合一致.     

Substitutional diffusion and Kirkendall effect in binary crystalline solids containing discrete vacancy sources and sinks

We investigate vacancy-mediated diffusion in a binary substitutional alloy by explicitly accounting for discrete vacancy sources and sinks. The regions between sources and sinks are treated as binary crystals with a perfect lattice structure containing a dilute concentration of vacancies. The sources and sinks are assumed ideal, maintaining an equilibrium vacancy concentration in their immediate vicinity. Diffusion within the perfect lattice is described with a diffusion-coefficient matrix determined by kinetic Monte Carlo simulations for a binary, thermodynamically ideal alloy in which the components have different vacancy-exchange frequencies. Continuum simulations are performed for diffusion couples with discrete grain boundaries acting as vacancy sources and sinks. Effective grain coarsening due to the Kirkendall effect is observed even in the absence of Gibbs-Thomson driving forces. As in standard ternary systems, uphill diffusion is observed. We also find that the drift of the lattice frame of reference as a result of the Kirkendall effect increases with the source/sink density. Upon increasing the density of vacancy sources and sinks, we recover the conventional treatment of substitutional diffusion, which assumes a dense and uniform distribution of vacancy sources and sinks that maintain an equilibrium vacancy concentration throughout the solid. The inverse Kirkendall effect, where the slower component segregates at grain boundaries acting as vacancy sinks, is also observed in the simulations.     

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.     

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.     

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.     

Morphological evolution and growth kinetics of Kirkendall voids in binary alloy system during deformation process—Phase field crystal simulation study

The formation and growth of Kirkendall voids in a binary alloy system during deformation process were investigated by phase field crystal model. The simulation results show that Kirkendall voids nucleate preferentially at the interface, and the average size of the voids increases with both the time and strain rate. There is an obvious coalescence of the voids at a large strain rate when the deformation is applied along the interface under both constant and cyclic strain rate conditions. For the cyclic strain rate applied along the interface, the growth exponent of Kirkendall voids increases with increasing the strain rate when the strain rate is larger than 1.0×10^?6, while it increases initially and then decreases when the strain rate is smaller than 9.0×10^?7. The growth exponent of Kirkendall voids increases initially and then decreases gradually with increasing the length of cyclic period under a square-wave form constant strain rate.     

锌对SnxZn/Cu界面微空洞的影响

通过向锡钎料中添加不同含量的Zn元素,系统研究了锌对SnxZn/Cu(x=0,0.2,0.5,0.8(质量分数,％))界面处柯肯达尔空洞形成的影响.结果表明,经热老化处理后,纯Sn/Cu接头中的Cu3 Sn层和Cu3 Sn/Cu界面出现了大量柯肯达尔空洞.然而随着Zn元素含量的增加,反应界面处的Cu3Sn层逐渐变薄甚至消失,柯肯达尔空洞也随之显著减少或消失;锌在反应界面处的富集现象越来越显著.锌参与了界面反应,形成了(Cu,Zn)6Sn5相、Cu6(Sn,Zn)5相和Cu-Zn固溶合金,其中Cu-Zn固溶合金层可以显著影响铜的界面扩散.Zn元素直接参与了界面扩散,在很大程度上缓和铜和锡的不平衡扩散,从而有效抑制了柯肯达尔空洞的形成.     

Investigation of interdiffusion and kirkendall effect in the Co-Ni-Fe system: III. Dependence of diffusion parameters on the initial conditions

Dependences of the parameters of interdiffusion (effective coefficients, diffusion paths, Kirkendall shift) on the variation of the initial compositions of a diffusion couple have been studied on the concrete example of the Co-Fe-Ni system. The experimental results obtained show that the diffusion paths in the three-component system depend substantially on the selection of initial conditions, even when the initial alloys of the “narrower” diffusion couple lie on the diffusion path of the “wider” pair. At the same time, when represented in reduced concentrations, the diffusion paths of all these diffusion couples practically coincide. The latter makes it possible to predict the type of diffusion paths for any diffusion couple whose initial com- position lies in the same concentration region. In one of the diffusion couples studied, the instability of the Kirkendall plane was revealed, which thus far was observed only in binary systems.     

The discovery and acceptance of the Kirkendall Effect: The result of a short research career

In the 1940s, it was a common belief that atomic diffusion took place via a direct exchange or ring mechanism that indicated the equality of diffusion of binary elements in metals and alloys. However, Ernest Kirkendall first observed inequality in the diffusion of copper and zinc in interdiffusion between brass and copper. This article reports how Kirkendall discovered the effect, now known as the Kirkendall Effect, in his short research career. Editor's Note: A hypertext-enhanced version of this article can be found at http://www.tms.org/pubs/journals/JOM/9706/Nakajima-9706.html. Also some of the artwork employed here was photographically reproduced from existing publications. As a result, the quality of the images is sometimes less than ideal.     

A physico-chemical approach in binary solid-state interdiffusion

A physico-chemical approach is developed, which can be used in binary diffusion couples to determine diffusion parameters of product phases with a wide homogeneity range, as well as phases with a narrow homogeneity range. It is demonstrated that this approach is basically equivalent to the diffusion-based treatment. However, the physico-chemical approach pedagogically sheds light on the chemical reactions occurring during interdiffusion at the interphase interfaces. This theory can be used in any binary system for any end-member condition to explain single-phase or multiphase diffusion-controlled growth. Ni–Al and Ag–Zn systems are considered here to calculate diffusion parameters following the physico-chemical approach. It is evident from our theoretical analysis and experimental evidence that in the case of presence of a stable Kirkendall marker plane one should expect the presence of duplex grain morphology in a particular phase layer.