Marko Hämäläinen

A thermodynamic analysis of the binary alloy systems Cu-Cr, Cu-Nb and Cu-V

Abstract Thermodynamic properties and the phase diagrams of the binary alloys Cu-Cr, Cu-Nb and Cu-V have been critically assessed by the Lukas program using simultaneously thermodynamic and phase diagram measurements. Thermodynamic measurements were available on chromium-copper alloys only. Thus the thermodynamic properties of the binaries copper-niobium and copper-vanadium were estimated by using entirely the phase diagram data. The excess Gibbs energies were expressed by Legendre polynomials. Distribution equilibria for solutes in the zone-melting of copper were utilized for adjusting the solid-liquid equilibria of the copper-rich alloys. The complete Gibbs energy expressions for the alloy phases were presented allowing calculation of the phase diagrams and the thermodynamic mixing properties of the phases.

Thermodynamic analysis of stable and metastable equilibria in the Cu-Cr system

Abstract The available experimental information is not sufficient to determine the temperature dependence of excess Gibbs energy of the liquid Cu-Cr alloys. The previously optimized excess entropy of mixing of the liquid phase is too positive. A new set of optimized thermodynamic functions of the Cu-Cr system has been obtained from thermodynamic and phase diagram data incorporating the latest data. The Tanaka-Gokcen-Morita relationship was used to constraint the excess enthalpy and entropy coefficients of the liquid phase. The optimized thermodynamic functions can account very well for the process of precipitation in the supersaturated fcc Cu-Cr alloys.

Lead activities and ternary miscibility gap in the CuPbFe liquid solutions

Abstract The transpiration method was used to measure the lead vapour pressure in liquid Cu-Pb-Fe alloys at the temperature 1723 K. The lead and iron concentration varied from 2.5 to 35 at.pct. Excess Gibbs energy in liquid ternary alloys was calculated from experimental results and literature data for binary solutions using Redlich-Kister-Muggianu formalism. The liquid miscibility gaps at the temperatures 1600 – 1900 K were determined by means of ThermoCalc program.

Optimisation of in-service performance of boiler steels by modelling high temperature corrosion – EU FP5OPTICORR project

The paper summarises the aims and development of EU-OPTICORR project in modelling of high temperature oxidation and corrosion. The work necessitates thermodynamic data collection and processing for the modelling tools. At present the tools are two ChemSheet based programmes with a kinetic module and easy to use interface and a more sophisticated numerical finite-difference based diffusion calculation programme, InCorr, developed for prediction of internal corrosion. Introduction The aim of OPTICORR project, started in 2001, is to develop a life-cycle approach (LCA) for the materials in energy production, particularly for the steels used in waste incinerators and co-fired boiler plants aiming at safe and cost effective energy production. The aims include: The control and optimisation of in-service performance of boiler materials, Understanding of HT corrosion and oxidation mechanisms under service conditions, Improvement of reliability to prevent the failure of components and plant accidents and Expanding the limits of boiler plant materials by corrosion simulations for flexible plant operation conditions (steel, fuel, temperature etc.). The project includes four technical work packages, where two first produce data for modelling of corrosion kinetics. The kinetics of high temperature oxidation and corrosion are determined from laboratory thermogravimetric tests (TG) and multi-sample exposure tests. The materials studied are typical boiler tubes and fin-steels: ferritic alloys, austenitic steel T347 and Ni-based alloy Inconel 625. The exposure gases are dry air, air with 15 vol-% H2O, and with 2000 ppm HCl and 200 ppm SO2. The salt deposits used are based on KCl-ZnCl2 and Ca,Na,K,Pb, Zn sulfate. The test temperatures for exposures with deposits are 320, 420 and for gas exposures 500, 550 and 600 oC. The tests have been carried out by the project partners, see the list of authors. The development of modelling tools for oxidation and high temperature corrosion is the most critical part in the project. The modelling has been started with thermodynamic data collection for relevant systems and thermodynamic mappings. The second step is to construct a model for the general high temperature oxidation of steels using ChemSheet [1] as the basis for the new kinetic tool development. The third level is simulation model and tool development for salt-induced hot corrosion based on ChemSheet approach. The most detailed kinetic modelling tool will be developed for internal corrosion simulation using InCorr programme [2]. Materials Science Forum Online: 2004-08-15 ISSN: 1662-9752, Vols. 461-464, pp 473-480 doi:10.4028/www.scientific.net/MSF.461-464.473

HT-XRD in the study of Cu-Li-Mg

In a previous study on Cu-Li-Mg system, the authors of the present paper concluded that the ternary phase in that system corresponds to CuMg2-xLix (x ~ 0.11), with a hexagonal structure, space group P6222 (180), and lattice parameters a = b = 0.5260 nm, c = 1.3649 nm [1]. The structure was refined by the Rietveld method [2]. In order to characterize the thermal behaviour of the ternary compound and to assess the Cu-Li-Mg phase diagram [3], HT-XRD measurements were performed on samples whose compositions were close to the one corresponding to the ternary compound. SEM/EDS measurements of the phases’ compositions in equilibrium, as well as DSC/DTA heating curves, contributed to the identification of the transition temperatures and the phases present in equilibrium. It was concluded that the ternary phase decomposes at ~ 702 ± 2K. Introduction The Cu-Li-Mg system has not been, till now, the object of many studies although it is one of the ternaries of the Al-Cu-Li-Mg system which has been deeply studied, at least near the quasicrystalline T2 (Al6Li3Cu) phase, and which has many applications in the aeronautic industry. Mel’nik et al. [4] referred to the existence of a ternary phase in the Cu-Li-Mg system: Cu8Li2Mg15 with an orthorhombic structure (a = 0.524 nm, b = 0.899 nm, and c = 5.433 nm). Hämäläinen et al. [3] assessed the phase diagram of the system. Figure 1 presents two vertical sections for x(Li) = 0.04 and x(Li) = 0.07 from the Gibbs energy parameters obtained in [3]. In previous work, the present authors pointed out the existence of a phase with a stoichiometry close to that of Cu8Li2Mg15 [5] and, in recent work, the latter phase was defined as being CuMg2-xLix (x ~ 0.11) [1]. Taking into account that there were no experimental data about the thermal behaviour of the ternary phase, nor the high temperature equilibria, 300 European Powder Diffraction Conference, EPDIC 10 and that quenching seemed ineffective for such a narrow temperature range, some HT-XRD studies were developed. On the other hand, an important feature for a successful assessment is the crystallographic data; thus the models used to describe the phases should be supported by the phase’s crystal structure.

Thermodynamic evaluation of the Cu-Mg-Zr system

The thermodynamic evaluation of the Cu–Mg–Zr system is presented in this paper. A literature survey was carried out first based on the most recent literature, which was scanned from the THERMET literature database. The evaluation of the thermodynamic parameters was carried out using Thermo-Calc (version H) software. The evaluation of the Cu–Mg–Zr system was carried out using the most recent experimental data from the literature and a set of DTA measurements. DTA measurements were done using alumina (Al2O3) crucibles under helium atmosphere with the niobium (Nb) reference crucible. The evaluated Cu–Mg–Zr phase diagram fitted well with experimental data with the liquidus data in a limited range of composition. There were two miscibility gaps observed in the system. New τ phase was detected using the X-ray and microscopic analysis and the data was used in this evaluation.

First principles, thermal stability and thermodynamic assessment of the binary Ni–W system

Abstract The Ni–W binary system was assessed using critically evaluated experimental data with assistance from first principles analysis and the CALPHAD method. The solution phases (liquid, fcc-A1 and bcc-A2) were modeled using the substitutional regular solution model. The recently discovered Ni8W metastable phase was evaluated as Fe16C2-like martensite with three sublattices, and shown to be possibly stable according to first principles calculations. Ni8W was also modeled as an interstitial compound, but the model is not good because the solubility of tungsten in nickel is very low, especially at low temperatures. There is no experimental evidence for such low solubility. The other binary compounds Ni4W and Ni3W were assessed as stoichiometric ones. Compared independent experimental and first principles data agree well with the calculated phase diagram using updated thermodynamic parameters.