Correlation between interfacial energy and phase diagram in ceramic-metal systems

Estimates of interfacial energies between ceramics (MX) and liquid metals (A) have been arrived at by employing an improved version of the Becker’s model for interfacial energy calculations at liquid metal-liquid metal interfaces to calculate the total energy of interatomic bonds across an interface. The results of such an approximation yield values that are very close to the experimental values; for instance, the estimated value for Al₂O₃/lFe is 2 J · m⁻², which compares well with the experimental data ranging from 1.9 to 2.3 J · m⁻². It is suggested that interfacial energies depend on two terms: (1) the formation energy of MX and (2) the pairwise interaction energies between M and A atoms and X atoms and vacant interstitial sites. It is also found that the calculated interfacial energies in eutectic systems (carbides-metal, etc.) are generally low, while those in the monotectic systems (oxides-metal, etc.) are generally high.     

Sn-37PbNi界面反应行为的相图计算分析

采用Thermo-Calc软件及相关数据库,将相图计算应用到Sn-Pb共晶焊料与Ni基体的界面反应行为的分析当中.依据局部平衡理论,通过亚稳平衡状态的计算和中间相形成驱动力大小的比较,预测出了500 K焊接温度下Sn-37Pb与Ni基体界面处金属间化合物的形成序列为Ni3Sn4→Ni3Sn2→Ni3Sn.通过Sn-Pb-Ni三元系500 K和423 K下等温截面的计算,预测出了润湿反应和固态时效反应过程中系统的相转变的情况.计算与试验结果吻合较好.     

Thermodynamic database development-modeling and phase diagram calculations in oxide systems

The databases of the FactSage thermodynamic computer system have been under development for 30 years. These databases contain critically evaluated and opthnized data for thousands of compounds and hundreds of multicomponent solutions of solid and liquid metals, oxides, salts, sulfides, etc. The databases are automatically accessed by user-friendly software that calculates complex multiphase equilibria in large multicomponent systems for a wide variety of possible input/output constraints. The databases for solutions have been developed by critical evaluation/optimization of all available phase equilibrium and thermodynamic data. The databases contain parameters of models specifically developed for different types of solutions involving sublattices, ordering, etc. Through the optimization process, model parameters are found which reproduce all thermodynamic and phase equilibrium data within experimental error limits and permit extrapolation into regions of tempea＇ature and composition where data are unavailable. The present article focuses on the databases for solid and liquid oxide phases involving 25 elements. A short review of the available databases is presented along with the models used for the molten slag and the solid solutions such as spinel, pyroxene, olivine, monoxide, corundum, etc. The critical evaluation/optimization procedure is outlined using examples from the Al203-SiO2-CaO-FeO-Fe2O3 system. Sample calculations are presented in which the oxide databases are used in conjunction with the FactSage databases for metallic and other phases. In particular, the use of the FactSage module for the calculation of multicomponent phase diagrams is illustrated.     

RE-X二元合金相图的热力学数据库

利用CALPHAD方法,采用亚正规溶体模型、亚点阵模型以及理想气体模型来描述RE-X(Ag,Bi,Cr,Mn,Mo,V,Zn)中二元系各相的Gibbs自由能,并结合相平衡及热力学性质的实验结果,对Ag-RE(RE:Sc,Y Nd,Sm,Gd,.Tb,Ho,Er)、Bi-RE(RE:Nd,Tm,Er,Ho,Pr,Gd)、...     

Tight-binding calculations of cohesive properties and phase diagram of Ni-Al-X alloy systems

A tight-binding recursion scheme, coupled to the linear muffin-tin orbital method, is used to study the chemcial bonding and thermodynamical properties of Ni-Al-X bcc alloys, where X denotes solute elements such as Mn, Fe, and Co. The electronic structures are calculated by tridiagonalizing a tight-binding Hamiltonian using the continued fraction technique. The authors estimate the effective pair (cluster) interaction energies V_Ni-Al V_Al-X and V_Al-x using the direct configurational averaging method and discuss the effects of the ternary solute atoms on the thermodynamical properties of the Ni-Al-X alloys, using the cluster variation method. The effective pair interaction energies are calculated by averaging over a small number of randomly generated configurations.     

Transition metal- chalcogen systems XI: the platinum- selenium phase diagram

The platinum-selenium phase diagram was investigated by differential thermal analysis, metallography, and X-ray powder diffraction methods. The two previously known intermediate phases, Pt₅Se₄ and PtSe₂, both melt congruently: Pt₅Se₄ at ∼1070 °C and PtSe₂ (under its own vapor pressure) at 1245 ± 10 °C. Pt₅Se₄ forms a eutectic with Pt at 1065 ± 2 °C and ∼42 at % Se and another one with PtSe₂ at 1067 ± 2 °C and somewhat below 45 at.% Se. On cooling, Pt and PtSe₂ form a metastable eutectic at 1037 ± 2 °C and ∼43 at % Se. Between PtSe₂ and Se, a degenerate eutectic was found at 221 °C, which also indicates negligible solubility of platinum in solid selenium.     

Determination of the interfacial energy ratio in two-phase systems by measurement of interphase contact

For a system of spherical particles in a matrix, a relationship is derived between the equilibrium degree of particle contact and the ratio of the interfacial energies, i.e., the energy of the contact boundary between particles and of the particle-matrix interface. The degree of particle contact is expressed in terms of the contiguity and the average number of contacts per particle, both of which can be measured by counting on planar sections. Thus the relationship provides an alternative to the measurement of dihedral angle for the determination of the energy ratio. The method is applied to the systems TiC-Co, TaC-Co, and WC-Co and, in combination with wetting data, is used to estimate the surface and interfacial energies in these systems.     

Efficient phase diagram information and computational thermodynamics

Industries that process and use metals, from microelectronics to aerospace, can use phase equilibria data for designing and processing complex alloys (three or more components) and diffusion data for controlling the formation and dissolution of precipitate phases within a matrix or at an interface. The number of images or data tables that would be needed for the graphic representation of such data is prohibitively large for systems with a large number of components. Databases that store thermodynamic and diffusion data as analytical functions provide a compact, retrievable storage method. They also permit the extrapolation of properties from binary and ternary systems to higher-order systems based on a physical model. Special task software that allows the nonexpert to extract the required information has been developed for the casting of superalloys and the solidification of Pb-free solders. Examples of user-friendly data representation and data utilization in advanced applications are presented. This paper was presented at the International Symposium on User Aspects of Phase Diagrams, Materials Solutions Conference and Exposition, Columbus, Ohio, October 18–20, 2004.     

Effect of annealing on the interfacial adhesion energy between electroless-plated Ni and polyimide

The effect of annealing on the interfacial adhesion energy between electroless-plated Ni films and polyimide substrates was evaluated using a 180-degree peel test. The measured peel strength values decrease from 263.6 ± 7.8 J/m² to 109.3 ± 6.4 J/m² after annealing for 100 h at 200 °C in an ambient environment. XPS analysis on the peeled surfaces reveals that the peeling is due to cohesive failure inside the polyimide, which is related to the fact that wet treatment produces an activated bonding mechanism between electroless-plated Ni and polyimide. This implies a degradation of the polyimide structure due to oxygen diffusion through the interface between Ni and alkali wet-treated polyimide, which is also closely related to the decrease in the interfacial adhesion energy due to thermal treatment in ambient conditions.     

Correlation between stacking fault energy and deformation microstructure in high-interstitial-alloyed austenitic steels

The correlation between stacking fault energy (SFE) and deformation microstructure of high-interstitial-alloyed austenitic Fe–18Cr–10Mn–(N or N + C) alloys was investigated. As the content of the interstitial elements increased, the deformation microstructure changed in a sequence strain-induced martensitic transformation, mixture of martensite and twin, and finally deformation twin. The SFE, playing an important role in the transition of deformation microstructure, was evaluated by the Rietveld whole-profile fitting combined with the double-Voigt size–strain analysis for neutron diffraction profiles of tensile-strained bulk samples. At fixed N + C content, the ratio of mean-squared strain to stacking fault probability remained constant regardless of the accumulated strain, whereas the ratio gradually increased with increasing N + C content. Almost linear dependence of measured SFE on N + C content could be established. According to the SFE, deformation bands exhibited distinct substructures, and their particular intersecting behavior resulted in the formation of different types of products (secondary ε martensite, α′ martensite and secondary twin) at the intersecting regions.     

The diffusion couple technique in phase diagram determination

The diffusion couple technique is a valuable experimental approach in studying phase relations in multicomponent systems. The use of different modifications of the method is illustrated by examples of phase diagram determination in various ternary systems. It is also shown that a number of error sources may appear when multiphase diffusion experiments are employed for constructing isothermal cross-sections. The difficulties connected with the concentration measurement at the interfaces and problems associated with the formation of a quasi-equilibrated diffusion zone are discussed. It is demonstrated that the efficiency of the diffusion couple technique is very high. However, in order to increase the reliability of the information obtained about a ternary diagram, a combination of the diffusion methods with an investigation of selected alloys is desirable.     

Ce-La-O体系相图热力学及应用(英文)

采用实验测量和热力学计算相结合的方法,系统研究Ce-La-O体系相图热力学和Ce-La合金的氧化反应过程。制备一系列不同成分的CeO2-LaO1.5混合物并对其进行X-射线衍射分析,获得了LaO1.5与CeO2在1273K时的相互固溶度;利用该研究测量以及文献报道的实验数据,优化了CeO2-LaO1.5体系相图;结合已有的Ce-O和La-O体系热力学描述,计算了Ce-La-O体系状态图并解释了Ce-La合金的氧化反应过程,发现只要La含量不超过80%,Ce-La合金被氧化后均形成CeO2为基的固溶体。