Papers by Author: J. Vřeštál

Abstract: Ab initio electronic structure theory has achieved considerable reliability concerning predictions of physical and chemical properties and phenomena. It provides understanding of matter at the atomic and electronic scale with an unprecedented level of details and accuracy. In the present contribution, the electronic structure theory and state-of-the-art ab initio calculation methods in solids are briefly reviewed and the application of the calculated total energy differences between various phases (lattice stabilities) is illustrated on construction of phase diagrams by the CALPHAD (CALculation of PHAse Diagrams) method in systems containing phases with complex structures, as e.g. Laves phases or sigma phase. Particular examples include description of the Laves phases in the Cr-Nb, Cr-Ta and Cr-Zr systems, sigma-phase in the Fe-Cr system and prediction of the phase composition of ternary Fe-Cr-Mo system and super-austenitic steels. It is shown that the utilization of ab initio results introduces a solid basis of the energetics of systems with complex phases, allows to avoid unreliable estimates and extrapolations of Gibbs energies and brings more physics into the CALPHAD method.

Abstract: Interaction of lead-free solders with copper substrate represents an important phenomenon in the issue of reliability of solder joints. New experimental data describing phase equilibria in the Cu-In-Sn system after long-time diffusion annealing at the 400 °C/50 hours, 600 °C/310 hours and 600 °C/48 hours will be presented. The composition of solders was: 100 % Sn, 75 % Sn + 25 % In, 50 % Sn + 50 % In, 25 % Sn + 75 % In, 100 % In. The fast quenching method was employed to freeze thermodynamic equilibrium after annealing, followed by metallography, microhardness measurements, SEM (Scanning Electron Microscope) and WDX (Wave Dispersive X-ray) analysis. New phase equilibrium data, together with the data from literature, represent the best existing experimental description of phase equilibria in the system in question. The obtained experimental results of the phase equilibria were compared with the thermodynamic modelling by the CALPHAD (Calculation of Phase Diagrams) method and with other authors.