A. Khvan

Critical Assessment 5: Thermodynamic data for vacancies

Abstract The thermodynamic properties of crystalline phases are generally represented well in terms of the compound energy formalism and the model has been implemented in all the major software packages used to calculated phase equilibria. The formalism is particularly successful in modelling defects in crystals, both the formation of holes or vacancies on lattice sites, and the dissolution of atoms on interstitial sublattices. In the former case the formalism may require the definition of data for pure vacancy itself. In this assessment we investigate the possible values for the Gibbs energy of vacancy to be used in the compound energy formalism and show that a value of zero or negative will always lead to unwanted catastrophic stability of the phase.

Prediction of solidification behaviour and microstructure of Ni based alloys obtained by casting and direct additive laser growth

Numerical tools are now used widely in the prediction of material properties necessary in order to gain a better understanding of the relationship between material properties and performance, to improve the reliability of processes and the quality of the final product, and to reduce costs, waste and energy use. In this paper, the solidification properties and the microstructure of some commercial Ni based alloys were analysed and predicted numerically using the ProCAST software. The microstructure of a sample obtained by the direct additive laser growth, a new additive manufacturing technique based on the selective laser melting, is presented and discussed. Numerical approaches and software packages that can be used to model additive manufacturing processes are discussed and critically analysed.

Experimental Investigation and Modeling of Copper Smelting Slags

Effective extraction of copper from sulfide ores requires careful operation of a copper smelter, which in turn depends very much on chemistry of the feed and resulted slag and matte. For example, chemical composition of copper smelting slags has to be in a certain range to ensure that their properties are within specific limits. Disobeying these rules may lead to complications in smelting operation, poor quality of the copper products, and premature shutdown of the copper smelter. In the present paper the microstructure and phase composition of slags from the Almalyk copper flash smelter were investigated experimentally and then modeled thermodynamically to evaluate potential ways of improvement and optimization of the copper smelting process and its products. The slag samples were taken at different stages of the copper smelting process: on slag tapping, after slag transportation to a deposition site, and at the site. Experimental investigation included the XRD, XRF, and SEM techniques, which were also confirmed by the traditional wet chemistry analysis. Thermodynamic modeling was carried out using thermochemical software package MTDATA, which enables thermodynamic and physical properties of the matte, slag, and gas phases to be calculated in a wide range of temperatures, pressures, and chemical compositions. In addition, slag viscosities and corresponding matte settling rates were estimated using the modified Urbain and Utigard–Warczok models, and the Hadamard–Rybczynski equation, respectively. It was found that the copper content in the slags may vary significantly depending on the location of slag sampling. Cu was found to be present as sulfide particles, almost no Cu was found to be dissolved in the slag. Analysis of microstructure and phase composition showed that major phase found in the samples is fayalite, while other phases are complex spinels (based on magnetite), different sulfides, and a glass-like phase. Thermodynamic calculations demonstrated the presence of these phases, their compositions, and optimal ranges of operating conditions. Potential ways of improving the matte grade and optimizing the smelting process were suggested on the basis of the calculations.

Oxide formation during electric resistance welding of low carbon steels

The influence of Mn and Cr on the formation of surface oxides and their entrapment during electric resistance welding of Si containing low carbon steels was studied using thermodynamic calculations and experimental investigation of the microstructure of the different oxide inclusions within welds on electric resistance welding-fabricated pipes. The process of oxidation during the welding process, its dependence on oxygen content, temperature of oxidation and the composition of ferrite within the parent steel were analysed. It was shown that the most important influence on the type of oxide inclusions formed during welding is the Mn/Si ratio, while Cr has an indirect influence via carbide formation, which increases the relative content of Mn in ferrite.

Transforming of the Morphology of Iron Phases in Aluminum Alloys

Iron containing phases with unfavorable morphology almost always exist in commercial aluminum alloys. The attempt to change morphology of the iron containing phase by addition of different alloying elements was made in present work. Experimental and thermodynamic studies of multicomponent phase diagrams with additions of refining elements were carried using ThermoCalc software and analysis of microstructures of the alloys in as-cast and annealed states. The possibility to obtain iron containing phases with almost spherical morphology, which allows to neutralize negative influence of iron on ductility and fracture strength of alloy, was presented in the work.