On aliovalent cations control of α-alumina growth on doped and undoped NiAl
Journal article, 2021

Alumina forming Ni-base superalloys are essential due to their oxidation resistance at elevated temperatures. A two-step procedure allows to assess the outward growth of the oxide scale from the resulting oxide ridges that form at 1100°C and cap the alumina grain boundaries. Employing undoped 50Ni50Al (at%) as reference, the impact of reactive elements on the diffusion processes, here Zr and Hf, is quantified using atom probe tomography. Unexpectedly, we find that up to one monolayer of Ni may co-decorate the alumina grain boundaries. Additionally, a decrease in Al-, and Ni-diffusivity of two orders of magnitude is observed owing to the reactive element effect. We employ density functional theory calculations to better understand the role of aliovalent cations, here Ni(II), Zr(IV), and Hf(IV) in the α−alumina scale. The calculations show that Ni may not only decorate the alumina grain boundaries but also facilitates transport of electrons as well as oxygen vacancies. Thereby oxide scale growth becomes enhanced. In turn, the dual impact of reactive elements, i.e. to annihilate oxygen vacancies and to remove impurity states in the band gap, explains the reduced scale growth rate.

Oxidation

Atom-probe tomography

Nickel superalloys

Density functional theory

Grain boundary diffusion

Author

Torben Boll

Karlsruhe Institute of Technology (KIT)

Materials Microstructure

Vedad Babic

Chalmers, Chemistry and Chemical Engineering, Energy and Material, Environmental Inorganic Chemistry 2

Itai Panas

Chalmers, Chemistry and Chemical Engineering, Energy and Material, Environmental Inorganic Chemistry 2

Olof Bäcke

Chalmers, Physics, Microstructure Physics

Marta Krystyna Stiller

Chalmers, Physics, Microstructure Physics

Acta Materialia

1359-6454 (ISSN)

Vol. 210 116809

Subject Categories

Inorganic Chemistry

Ceramics

Metallurgy and Metallic Materials

DOI

10.1016/j.actamat.2021.116809

More information

Latest update

4/28/2021