Thermochemical Modeling of Laves Phase Containing Ferritic Steels
Buch in deiner Nähe kaufen
Beschreibung
For energy technology, development of new materials is required to be used for boiler and steam turbines
with high thermal cyclability, creep strength and excellent corrosion resistance in steam and high
temperatures and also at downtime in water. Crofer 22H, a new kind of steel jointly developed at
Forschungszentrum Juelich and Thyssen Krupp, has already shown promising results in laboratory tests.
The formation of Laves phase particles improves the material’s properties such as creep strength while
the high Cr-content of 22 % provides excellent corrosion resistance. Unfortunately, the formation of
Laves phase competes with the formation of other phases. In order to further improve this type of ferritic
steels, knowledge of thermodynamics of the intermetallic systems forming the Laves phases
(Fe,Cr,Si)2(Nb,W) is required for the calculation of phase stability as a function of composition and
temperature. The Calphad method is of great help for the calculation of phase stability in technical
materials. This kind of calculation is based on thermodynamic databases. Calculations with the
commercial steel database have shown to be inaccurate since not all considered alloy systems have been
modeled up to now. The present work aims to provide a thermodynamic optimization of the systems
containing Laves phases.
Thermodynamic data of Laves phase containing systems were obtained by the Calphad method with an
optimization of the sub-systems containing Laves phases. The Calphad method relies on the input data for
the considered system, their quality and their quantity are of primary importance for the obtained
thermodynamic assessment. In the present work, several methods have been used in order to provide
consistent thermodynamic calculations of the phase equilibria.
A combined experimental and modeling approach was chosen to determine the phase equilibria and
thermodynamic properties in the systems Fe-W, Cr-Nb, Cr-Fe-Nb and Fe-Nb-Si. DFT calculations were
done for all mentioned systems for the determination of the energy of formation of the compounds
through the chosen model. In the Fe-W system, in addition to the DFT calculations which are restricted to
0 K, phonon calculations were performed in order to obtain the temperature dependence of the Gibbs
energies which were used to improve the Calphad modeling
Autor*in
Aurélie Jacob
Themen in »Thermochemical Modeling of Laves Phase Containing Ferritic Steels«
Calphad method Laves Laves Phase