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A. Redermeier, E. Povoden-Karadeniz, E. Kozeschnik:
"Thermodynamic description of TCP phases in commercial Ni-base superalloys";
Talk: EUROMAT 2015, Warszawa; 2015-09-20 - 2015-09-24.

To enhance the creep resistance of single crystal Ni-base superalloys by solid-solution-strengthening, refractory metals, such as Re and W, are added. Unfortunately, these elements also promote the occurrence of topologically close-packed (TCP) structures, which deteriorate the mechanical properties of the superalloys. A variety of competing phases has been observed at typical service temperatures of modern Ni-base superalloys. However, theoretical predictions of their relative stabilities and compositions are disputed up to now. Here, we utilize information from experimental phase diagrams in combination with thermodynamic data evaluated by first-principles analysis to assess the stabilities of TCP phases in binary and ternary systems with relevance for 5th generation Ni-base superalloys. Finally, we combine the descriptions of subsystems to a multi-component database. The comparison of our predictions with various reported phase stabilities in industrial multicomponent Ni-base alloys shows good agreement. With our consistent modeling base, the role of mu-phase, R-phase, P-phase, sigma and delta-hcp TCP-phases as a function of alloy compositions and temperatures in industrially used Ni-base superalloys is discussed.

TCP phase, Ni-base superalloys, CALPHAD