Application of combinatorial materials science methods to model alloys for the understanding of phase stabilities and oxidation behaviour in Ni-Al-Cr and Ni-Al-Co

Dennis Naujoks, RUB, Bochum, Germany
Alfred Ludwig, RUB, Bochum, Germany
Martin Weiser, FAU, Erlangen, Germany
Sannakaisa Virtanen, FAU, Erlangen, Germany
Christina Eberling, RUB, Bochum, Germany

Ni-base superalloys are widely used for high temperature applications such as turbine blades in airplane or stationary gas turbines. Increasing the service temperatures of a gas turbine leads to higher efficiency. This results in a demand of advanced alloys that can operate in harsh and aggressive combustion environments. Ni-base superalloys are most commonly used in this field. Since the discovery of the stable L12 phase in Co-based systems (Co-Al-W / Co-Al-W-Ti), Co-base systems came back into focus. Co has a higher melting point than Ni and therefore Co-based superalloys are promising to the further increase of achievable working temperatures in gas turbines. For both Ni- as well as Co-base superalloys the understanding of thermodynamic equilibria and kinetic processes is very important.

Here, the combinatorial materials research approach of our group (Werkstoffe der Mikrotechnik, RUB) helps to explore the impact of various elements on the phase stability of desired (e.g. the oxidation resistant phase) and undesirable phases (e.g. TCP phases). Due to high throughput fabrication and analysis, wide composition areas were studied. This involves the formation of solid solutions and intermetallic compounds in the ternary metallic systems such as Ni-Al-X, Co-Al-X and Ni-Co-X (X=Ni, Al, Co, Cr, Re, Ru, W, Ti). Additionally, oxidation behaviour and surface effects were analysed. A recent study of intermediate Co/Ni model alloys showed an interesting influence of the Co to Ni ratio in the base material on the oxidation behaviour.

Regarding alloying elements, Al is outstanding, since it is essential for the precipitation of the secondary γ’ phase as well as the formation of protective oxide scales at high temperatures. Besides Al, Cr is also an important alloying element since Cr2O3 also contributes to the formation of stable oxide scales. In the following poster the concept of combinatorial materials research will be explained along with some of the newest results of our project (B5 SFB TR 103) on phase formation and oxidation behaviour in the ternary systems Ni-Al-Co and Ni-Al-Cr.

The authors acknowledge financial support from the Deutsche Forschungsgemeinschaft (DFG) within the collaborative research center SFB TR103 (project B5 and A5).

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