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Abstract

The σ-phase has a complex crystal structure, (prototype FeCr, Strukturbericht D_8b, Person Symbol tP30, Space Group 136), with an unit cell of 32 atoms distributed in 5 distinct sublattices. This phase is frequent in several materials specially in Steels and Ni-Superalloys. Usually it presents a range of homogeneity, it is an ordered solution phase which does not disorder.

σ is brittle and to control its formation in stable or metastable states is desirable in alloy design and production. For that its thermodynamic stability with respect to other phases present in such materials as well as their kinetic interlaced behavior should be well understood.

The sigma phase will be used here to illustrate how experimental and first-principles information can be used in order to construct Gibbsian databases using the CALPHAD method.

These databases can provide relevant information for microstructure simulations specially if they are coupled to kinetics databases. This procedure allows finally to connect crystal energetics to microstructure evolution in a complex alloy with many elements and phases.