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E. Povoden-Karadeniz, A. Redermeier, E. Kozeschnik:
"Hcp-structured delta phase in new generation single crystal Ni-base superalloys - predicted stability by thermodynamic modeling";
Poster: Modelling and Simulation of Superalloys 2017, Bochum, Deutschland; 2017-03-29 - 2017-03-31.

One of the refractory elements for improved high-temperature creep properties of single-crystal Ni-base superalloys is Rhenium. In order to suppress associated stabilization of brittle TCP-phases, 4^th to 6^th generation superalloys are alloyed by Ruthenium in addition. Ru has been reported to thermodynamically decrease the stabilities of topologically close-packed (TCP) phases, resulting in their suppression in fine-tuned alloy compositions. However, combining Re and Ru, disordered hexagonally close-packed solid solution phase (space group P63/mmc, Mg-prototype), in Ni-base superalloys often denoted as delta-phase, is promoted to form in the face-centered cubic Ni-matrix. This structure is clearly distinguished from the TCP phases consisting of Frank-Kasper coordination polyhedra. The thermodynamic base of hcp-phase stabilization in technological new generation Ni-base superalloys is presented and discussed based on computational thermodynamic modeling.

Ni-base superalloys, TCP phase, delta phase, CALPHAD