Thermodynamic database of the phase diagrams in the Mg-Al-Zn-Y-Ce system

The Mg-Al-Zn-Y-Ce system is one of the key systems for designing high-strength Mg alloys. The purpose of the present article is to develop a thermodynamic database for the Mg-Al-Zn-Y-Ce multicomponent system to design Mg alloys using the calculation of phase diagrams （CALPHAD） method, where the Gibbs energies of solution phases such as liquid, fcc, bcc, and hcp phases were described by the subregular solution model, whereas those of all the compounds were described by the sublattice model. The thermodynamic parameters describing Gibbs energies of the different phases in this database were evaluated by fitting the experimental data for phase equilibria and thermodynamic properties. On the basis of this database, a lot of information concerning stable and metastable phase equilibria of isothermal and vertical sections, molar fractions of constituent phases, the liquidus projection, etc., can be predicted. This database is expected to play an important role in the design of Mg alloys.     

Fe-Ti二元体系的热力学重新优化(英文)

为提高Fe-Ti二元系外推到三元或多元体系的能力,应用CALPHAD方法重新优化了该二元系。与前人的优化工作相比,重点放在对两个二元金属间化合物Fe2Ti和FeTi的热力学描述上。因目前普遍采用双亚点阵模型来描述C14_Laves相,所以采用双亚点阵模型来描述Fe2Ti相。通过检验包含Fe-Ti二元系的三元体系Fe-Ti边界上Fe2Ti相的均匀化范围进一步证实了Fe2Ti相的相边界。FeTi相具有BCC_B2晶体结构,因而将其处理成为BCC_A2相的有序相,并且用统一的Gibbs 能函数来描述有序和无序相。另外一个特别关注的方面就是重现这两个化合物的实测热容。计算结果与有关相图和热力学性质实验结果的广泛对比显示两者符合得很好,从而证明了所得热力学描述的有效性。     

Experimental determination and thermodynamic calculation of phase equilibria in the Fe−Mn−Al system

The phase equilibria among the face-centered cubic (fcc), body-centered cubic (bcc), and βMn phases at 800, 900, 1000, 1100, and 1200 °C were examined by electron probe microanalysis (EPMA), and the A2/B2 and B2/D0₃ ordering temperatures were also determined using the diffusion couple method and differential scanning calorimetry (DSC). The critical temperatures for the A2/B2 and B2/D0₃ ordering were found to increase with increasing Mn content. Thermodynamic assessment of the Fe−Mn−Al system was also undertaken with use of experimental data for the phase equilibria and order-disorder transition temperatures using the CALPHAD (Calculation of Phase Diagrams) method. The Gibbs energies of the liquid, αMn, βMn, fcc, and ε phases were described by the subregular solution model and that of the bcc phase was represented by the two-sublattice model. The thermodynamic parameters for describing the phase equilibria and the ordering of the bcc phase were optimized with good agreement between the calculated and experimental results. This paper was presented at the International Symposium on User Aspects of Phase Diagrams, Materials Solutions Conference and Exposition, Columbus, Ohio, 18–20 October, 2004.     

Thermodynamic modeling of the Au-Sb-Si ternary system

Thermodynamic optimization of the Au-Sb binary system was updated as well as the Si-Sb binary system was assessed thermodynamically using the CALPHAD method based on the critical review of the available experimental information from the published literature. The solution phases including liquid, fcc_A1(Au), diamond_A4(Si) and rhombohedral_A7(Sb), are modeled as substitutional solutions and their excess Gibbs energies are expressed by a Redlich-Kister polynomial. The solubility of Si in the intermetallic compound AuSb₂ is not taken into account because of the lack of experimental information. Combined with previous assessment of the Au-Si binary system, thermodynamic modeling of the Au-Sb-Si ternary system was performed to reproduce well the measured phase equilibria. The liquidus projection and several vertical sections of this ternary system were calculated, which are in reasonable agreement with the reported experimental data.     

Laser multi-layer cladding of Mg-based alloys

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Thermodynamic modeling of the Ru–Zr system

The Ru–Zr system has been critically assessed by means of the CALPHAD technique. Based on the experimental data, the solution phases (liquid, body-centered cubic, hexagonal close-packed) were initially modeled with the Redlich–Kister equation. It was shown that this model had a definite temperature range beyond which the liquid became unstable. To tackle the problem, the solution phases were modeled with a new semi-empirical equation, which was recommended by Kaptay. A two-sublattice model (Ru, Zr)_0.5(Ru, Zr)_0.5 is applied to describe the compound RuZr in order to deal with the order–disorder transition between body-centered cubic solution (A2) and RuZr with CsCl-type structure (B2). Another two-sublattice model (Ru, Zr)_0.6667(Ru, Zr)_0.3333 is applied to describe the compound Ru₂Zr in order to cope with the order–disorder transition between hexagonal close-packed (A3) and Ru₂Zr with MgZn₂-type structure (C14). A set of self-consistent thermodynamic parameters of the Ru–Zr system was obtained.     

Thermodynamic Modeling of the Succinonitrile-Water System

Succinonitrile-water (SCN-H₂O) system is a widely used transparent metallic alloy system due to its analog solidification behavior to metals. In the present work, Gibbs energy of pure succinonitrile was derived utilizing temperature as well as enthalpy of transformations, and temperature dependencies of heat capacity available in the literature. The phase diagram for the binary SCN-H₂O system was assessed via the CALPHAD approach using phase equilibrium data available in the literature. Self-consistent thermodynamic parameters were obtained. A good agreement between the experimental and calculated data for the phase diagram has been achieved. The present work contributes to the development of the thermodynamic database of the SCN-H₂O system that can be incorporated into thermodynamic and kinetic codes for computational simulations.     

Thermodynamic modeling of the Al–Cr system

By means of calculation of phase diagram (CALPHAD) technique, the Al–Cr system was critically assessed. Three solution phases (liquid, body-centered cubic, face-centered cubic) were modeled with the Redlich–Kister equation. The intermetallic compounds Al₇Cr, Al₁₁Cr₂, Al₄Cr, Al₈Cr₅, AlCr₂, which have a homogeneity range, were treated as the formulae Al₇(Al,Cr), Al₁₁(Al,Cr)₂, Al₄(Al,Cr), (Al,Cr)₈(Al,Cr)₅, (Al,Cr)(Al,Cr)₂ using two-sublattice model, respectively. A set of self-consistent thermodynamic parameters describing the Gibbs energy of each individual phase as a function of composition and temperature for the Al–Cr system was obtained.     

Thermodynamic assessment of the Ni-Sb binary system

The Ni-Sb binary alloy system was thermodynamically assessed using CALPHAD approach in this article.Excess Gibbs energies of solution phases,liquid and fcc phases,were formulated using the Redlich-Kister expression.The intermediate phases were modeled by the sublattice model with (Ni,Va)0.5(Ni,Sb)0.25(Ni)0.25 for Ni3Sb_HT phase and (Ni,Va)0.3333(Sb)0.3333(Ni,Va)0.3333 for NiSb phase.The other phases including Ni3Sb,Ni7Sb3,and NiSb2 were treated as stoichiometric compound owing to their narrow composition ranges.Based on the reported thermodynamic properties and phase diagram data,the thermodynamic parameters of these phases were optimized,and the obtained values can reproduce the available experimental data well.     

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)、...     

AZ31镁合金表面磷酸盐-高锰酸盐化学转化膜性能的试验研究

用磷酸盐-高锰酸盐在AZ31镁合金表面制备出无铬化学转化膜,并采用金相显微分析、扫描电镜分析、能谱分析、X-射线衍射分析、电化学方法、中性盐雾试验分别对化学转化膜封孔处理前后的表面形貌、成分、相结构和耐蚀性进行检测和评价.研究结果表明,无铬化学转化处理可以显著提高镁合金的耐蚀性,封孔后处理可以有效地封闭化学转化膜中存在的孔隙,并进一步提高镁合金的耐蚀性.     

Thermodynamic evaluation and optimization of the Ca−Si system

All available phase equilibria and thermodynamic data for the Ca−Si system were collected and critically evaluated. In a first step, the thermodynamic properties of Ca(g) were obtained from experimental vapor pressure data over pure Ca. The new vapor pressure of calcium over pure solid and liquid was used as a new reference to model the thermodynamic properties of the intermediate stoichiometric Ca−Si compounds together with other thermodynamic and phase diagram data found in the literature (liquidus temperatures, heat capacities, pressures of Ca, and heats of reaction). Optimization was performed to obtain the parameters of one set of model equations for the different solid and liquid phases to best reproduce all the experimental data simultaneously. In this way, the data are rendered self-consistent, discrepancies among the data are identified, and extrapolations and interpolations can be performed. For the liquid phase, the Modified Quasichemical Model in the Pair Approximation for short-range ordering was used.     

Thermodynamic optimization of the boron-cobalt-iron system

A thermodynamic optimization of the boron-cobalt-iron ternary system is performed based on thermodynamic models of the three constitutional binary systems and the experimental data on phase diagrams and thermodynamic properties of the ternary system. The liquid, fcc_A1, bcc_A2 and hcp_A3 solution phases are described by the substitutional solution model. The three intermediate line compounds, (Co,Fe)B, (Co,Fe)₂B and (Co,Fe)₃B, are described by the two sublattice model. A set of thermodynamic parameters are obtained. The calculated phase diagram and thermodynamic properties are in reasonable agreement with most of the experimental data.     

Thermodynamic modeling of the Ca–Ag binary system

The Ca–Ag binary system has been assessed with CALPHAD approach based on experiment information about phase diagram and thermodynamic properties. The excess Gibbs energies of the solution phases including liquid, bcc and fcc were formulated with Redlich–Kister polynomial functions. The intermetallic compounds Ca₂Ag₉, Ca₂Ag₇, CaAg₂, CaAg, Ca₅Ag₃ and Ca₃Ag were treated as stoichiometric phases. Self-consistent thermodynamic parameters have been obtained and the calculated results agree well with most literature data. Several diagrams and tables concerning the Ca–Ag system are presented.     

Au-Ag-Al系相图的热力学优化和计算

使用计算相图方法(CALPHAD)计算Au-Ag-Al的三元相图时,三个边际二元相图(Au-Al,Au-Ag,Ag-Al)的准确性对三元相图的计算有很大的影响,目前Au-Al边际二元相图存在着一定的矛盾。在综合评估Au-Al体系实验数据的基础上,优化和计算了Au-Al合金体系的平衡相图,使用置换式溶体溶液模型描述Au-Al体系中液相、Bcc和Fcc相的吉布斯自由能,分别用亚点阵模型(Al)(Au)4、(Al)3(Au)8、(Al)(Au)2、(Al)(Au)和(Al,Au)2(Al,Au)描述AlAu4、Al3Au8、AlAu2、AlAu和Al2Au相,通过Pandat软件优化得到一组各相的热力学参数,计算得到的Au-Al相图与实验数据和热力学数据相吻合。结合Au-Ag和Ag-Al的热力学参数,计算了Au-Ag-Al液相面投影图和等温截面图,液相面投影图显示该三元系存在8个四相平衡反应,对Au-Ag-Al合金的研究具有指导意义。     

Cu-Ni-Sn三元系相平衡的热力学计算

基于Cu-Ni-Sn三元系的相平衡和热力学的实验信息,采用亚正规溶体模型描述液相和fcc相的Gibbs自由能,为了预测该体系中bcc相的A2-B2有序-无序转变,bcc相的Gibbs自由能采用双亚点阵模型进行描述.利用CALPHAD(相图计算)方法评估了Cu-Ni-Sn三元系各相的热力学参数,计算的富Cu侧相图和热力学性质与实验数据比较一致.并对该三元系中bcc相的A2-B2有序-无序转变及fcc相的溶解度间隙进行了计算.这些计算结果对利用析出强化以及Spinodal分解开发高强度和高导电性的新型Cu基合金的组织设计具有一定的指导意义.     

Critical Evaluation and Thermodynamic Optimization of the Binary Systems in the Mg-Ce-Mn-Y System

Critical evaluation and thermodynamic optimization have been carried out for the Mg-Ce, Mg-Mn, Mg-Y, Ce-Mn, Ce-Y, and Mn-Y binary systems. All phase diagrams and thermodynamic data such as enthalpies of mixing, heats of formation, etc., were considered to obtain one set of model parameters of the Gibbs energies of all phases, which can reproduce the experimental data within experimental error limits. For the liquid alloys, the Modified Quasi-chemical Model in the pair approximation was used to treat short-range-ordering.     

Thermodynamic assessment of the Nb-Ge system

The Nb-Ge binary system has been thermodynamically assessed using the CALPHAD (Calculation of Phase Diagrams) approach on the basis of the experimental data of both the phase equilibria and the thermochemical properties. The reasonable models were constructed for all the phases of the system. The liquid and the terminal solid solution phases, Bcc-(Nb) and Diamond-(Ge), were described as the substitutional solutions with Redlich-Kister polynomials for the expressions of the excess Gibbs free energies. The intermediate phases (Nb₃Ge), (Nb₅Ge₃), (Nb₃Ge₂) and (NbGe₂) with homogeneity ranges were treated as the sublattice models Nb_0.75(Ge,Nb,Va)_0.25, Nb_0.5(Nb,Ge)_0.125(Ge,Va)_0.375, (Nb,Ge)_0.222(Nb,Ge)_0.333Nb_0.333(Ge,Va)_0.111 and (Nb,Ge)_0.333(Nb,Ge)_0.667 respectively based on their structure features of atom arrangements. A set of self-consistent thermodynamic parameters for the Nb-Ge system was obtained. Using the present thermodynamic data, the calculation results can reproduce the experimental data well.