Thermodynamic assessment of the copper-hafnium system

The thermodynamic properties of phases and phase equilibria in the Cu-Hf system are described with the CALPHAD method. The set of self-consistent model parameters is based on the thermodynamic properties of liquid alloys, intermetallic compounds, and phase equilibria. The excess Gibbs energy of the liquid phase is described using an ideal associated solution model. The models of thermodynamic properties are used to describe possible metastable transformations such as glass formation in rapid quenching from the melt, formation of bulk amorphous alloys, and formation of supersaturated terminal solid solutions.     

多元系B2相的热力学描述

B2相广泛存在于铁基、钴基和镍基合金中.B2相的析出对于合金组织和性能具有重要影响.本文指出了合理描述B2相的热力学模型,并就如何简单有效地描述多元合金系中的B2相,以及如何处理在此过程中可能出现的各种问题,进行了深入的探讨和研究.     

Phase equilibria and thermodynamics of binary copper systems with 3d-metals. II. The copper-vanadium system

Thermodynamic assessment of the Cu-V system was carried out using the CALPHAD method. The excess heat capacity of the liquid phase was taken into account in the model of its excess Gibbs free energy. Excess thermodynamic properties of limiting solid solutions were represented by regular solution models. A self-consistent set of thermodynamic parameters was obtained using data on the mixing enthalpy and information on the phase equilibria. The thermodynamic properties of the phases and the phase diagram along with its metastable extension were calculated using this set of parameters. The thermodynamic model of the system was used in order to predict the composition limits of formation of supersaturated solid solutions prepared by highly nonequilibrium methods of synthesis. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(449), pp. 71–79, May–June, 2006.     

二元互不溶体系合金机械合金化的热力学研究进展

二元互不溶体系合金在机械合金化的非平衡态过程中能够形成过饱和固溶体、非晶和纳米相复合结构等亚稳相,并表现出与其微米尺度结构合金所不同的性能。综述了Alonso热力学模型和机械合金化在二元互不溶体系合金中制备亚稳相的热力学计算。     

Thermodynamics of Liquid Alloys and Metastable Phase Transformations in the Copper - Titanium System

We have used solution calorimetry at temperatures of 1573 K and 1873 K over broad concentration ranges to study the mixing enthalpy of Cu - Ti liquid alloys. The molar mixing enthalpies of the system are significant negative values. We have established the temperature dependence of the molar mixing enthalpies of the system: there is an increase in their exothermicity as the temperature is lowered. The significant negative mixing enthalpies of the system allow us to conclude that the chemical bonds are localized in the studied melts and consequently associates form. We tested this conclusion within ideal associated solution theory, which describes well the results obtained with a set of CuTi and CuTi₂ associates. Using the model obtained, we have calculated the excess thermodynamic functions of mixing (enthalpy, Gibbs free energy, heat capacity) for the liquid alloys. We estimated the Gibbs energies of fcc, bcc, and hcp solutions in the system by the CALPHAD method, using data from the initial sections of the phase diagrams and from the corresponding thermodynamic data. We have calculated the metastable phase equilibria between the limiting solid solutions and the liquid or supercooled liquid phase. It was shown that for the supercooled liquid and the amorphous phase, a broad concentration range of relative thermodynamic stability can be obtained. The concentration range of amorphization of Cu - Ti melts corresponds to the position of the metastable liquidus line and the T₀ line at temperatures close to the temperature range of amorphous solidification. __________ Translated from Poroshkovaya Metallurgiya, Nos. 5–6(443), pp. 67–80, May–June, 2005.     

Mechanism of Widmanstätten plate formation in chromium-rich CrNi alloys

The mechanism of formation of the Widmanstätten plates which have recently been found in chromium-rich CrNi alloys, and are quite similar to the typical “Bainitic” plates in copper and silver based alloys, is discussed here by combining experimental data on the composition ofthe Widmanstätten plate with thermodynamic calculations of the stable and metastable phase equilibria. The observed nickel concentration of the Widmanstätten plate is about 30 mass% higher than that of the original b.c.c. (α) matrix, but it is about 4 mass% smaller than that of the f.c.c. (γ) phase in equilibrium with the b.c.c. phase at the start of the plate formation. The possibility of plate-formation mechanisms based on martensitic transformations from b.c.c. or to f.c.c. or from b.c.c. to a metastable phase with the so-called 3R structure is unambiguously excluded from thermodynamic considerations. The precipitation of the metastable phase with the 3R structure is proposed as the most probable mechanism of Widmanstätten plate formation. This mechanism explains the composition of the plate as well as the temperature range and the region of alloy compositions, where the Widmanstätten plate formation has been observed.     

Thermodynamic analysis of the iron-copper system I: The stable and metastable phase equilibria

Thermodynamic and phase diagram data in the Fe-Cu system are evaluated. For the liquid and fcc phases, the Margules-type of equations is used. For the bcc phase, the same type of equation is used to describe the non-magnetic contribution to the Gibbs energy. In addition, a magnetic term is included. Using the thermodynamic equations derived from equilibrium data, the stable and metastable equilibria of this system are calculated. Agreement between the calculated and experimental phase diagram is good except for temperatures higher than 1720 K. For these temperatures, the calculated liquidus tends to be higher. The possibility of supercooling which may account for some of the lower temperatures measured should not be excluded. The calculated metastable miscibility gap of the liquid phase also agrees with the experimental data.     

Thermodynamic assessment of the Cu-Ti-Zr system. I. Cu-Ti system

The CALPHAD method is used for the thermodynamic assessment of the Cu-Ti system that bounds the ternary Cu-Ti-Zr system, which is capable of forming amorphous alloys. The self-consistent parameters of thermodynamic models of the phases are obtained from data on the phase equilibria and thermodynamic properties of liquid alloys and intermetallic compounds. The Gibbs energy of the liquid phase is described using the associated ideal solution model. To describe the thermodynamic properties of the Cu₄Ti and CuTi intermetallic compounds with homogeneity range, sublattice models are used. The calculated phase diagram of the system and the thermodynamic properties of the phases are in good agreement with experimental data.     

LiBr-TbBr3体系相图热力学评估

采用CALPHAD技术热力学评估、计算了LiBr-TbBr3体系在整个成分范围内的平衡相图,其中组元LiBr和TbBr3的热力学性质分别采用SGTE热力学数据库和作者近期的评估结果,LiBr-TbBr3体系的热力学数据则通过对已有相图、热力学实验数据的精确评估优化获得.计算结果与实验数据的比较表明,本工作建立的热力学数据能够很好地解释现有实验结果、具有较好的物理意义.