Chimie Métallurgique des Terres Rares
Institut de Chimie et des Matériaux Paris-Est
CNRS, Université de Paris
Modelling topologically close-packed phases: application to the Mo-Re system
The modelling of topologically close-packed (tcp) phases is extremely important given the presence of these phases in many systems of transition metals and therefore in complex functional alloys such as steels and superalloys. In the frame of Calphad assessments, the models should be able to reproduce both their possible compositions and actual configurational entropy. In this regard, the three most important tcp phases have been studied: μ, σ and χ [1-3]. In each case, in a quite large number of binary systems, the atom distribution on the different sites has been studied by crystallographic means. In particular, the Rietveld refinement method of X-ray powder diffraction data has been extensively used. Conclusions have been drawn concerning the rules driving the site occupancies. Consequently, models have been defined in terms of the number and multiplicity of the sites in which atom mixing can occur in a different manner, as well as the nature of the atoms occupying these sites.
These models have been used to model the Mo-Re system, an important system for Ni-based superalloys, in which two tcp phases, σ and χ, are present. An assessment is presented which reproduces the available experimental data .
 J.-M. Joubert and N. Dupin, Intermetallics, 12 (2004) 1373-1380.
 J.-M. Joubert, Prog. Mater. Sci., 53 (2008) 528-583.
 J.-M. Joubert and M. Phejar, Prog. Mater. Sci. 54 (7) (2009) 945-980.
 S.-A. Farzadfar, M. Levesque, M. Phejar and J.-M. Joubert, Calphad: Comput. Coupling Phase Diagrams Thermochem. 33 (2009) 502-510.
The seminar takes place at 10:45 a.m. in the ICAMS seminar room UHW 11/1102, Stiepeler Straße 129, 44801 Bochum.
For further information contact Hildegard Wawrzik, firstname.lastname@example.org