Place: CALPHAD XLII, San Sebastian, Spain
Dario Alfe, University College London, London, United Kingdom
Alain Pasturel, SIMAP, Saint-Martin d’Hères, France
Controlling the formation of Topologically Close Packed (TCP) phases in steels and Ni-based superalloys is important for their mechanical properties. They have also been extensively studied in the past using first-principles methods, but mostly at 0 K. Only a few works have been done for the vibrational properties [1,2] and the importance of vibrational contributions on the stability of TCP phases is still under debate. Furthermore, the mechanical (in)stability of TCP phases in all possible configurations has not been studied yet.
In our previous work [3, 4], we have computed thermodynamic properties, site occupancies and phase diagrams as a function of temperature and composition in several binary systems and in the Cr-Ni-Re and Cr-Mo-Re ternary systems using a generalized Bragg-Williams-Gorsky approximation (BWG). In the present work we extend our previous results by computing the vibrational properties of the σ-phase in the ternary Cr-Ni-Re system in the harmonic approximation. Atomic forces were obtained from DFT calculations, using the VASP code. To analyse the importance of anharmonic contributions, we performed Ab Initio Molecular Dynamics (AIMD) calculations. Among the possible 243 ternary configurations obtained by permutations of the constituent atoms in the σ-phase structure, we have selected 3 binary Cr-Re configurations and 3 ternary Cr-Ni-Re configurations. The selected ternary configurations correspond to the stable ones at 0 K according to our previous study.
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