Surface Rumpling Behavior of Hf/Zr Single-Doped and Co-Doped β-NiAl Coatings during High-Temperature Cyclic Oxidation

Reactive elements like Hf- and Zr-doped β-NiAl are considered to be promising candidate materials for protective coatings used at ultra-high temperatures. However, the role of reactive element co-doping on cyclic oxidation behavior and the surface rumpling of β-NiAl coatings remains unclear. Thus, in this paper, Hf and Zr single-doped and co-doped β-NiAl coatings were deposited on a single crystal superalloy by electron beam physical vapor deposition and the cyclic oxidation at 1150 °C was investigated. The coatings yielded a similar oxidation rate during cyclic oxidation. Obvious surface rumpling appeared in the single-doped coatings, whereas it was effectively alleviated in the co-doped coating. Related mechanisms were discussed, including thermal expansion mismatch, martensitic transformation and phase transformation from β-NiAl to γ′-Ni3Al. The non-uniform phase transformation from β to γ′ was finally believed to be responsible for the discrepancy in the rumpling extents between the single-doped and co-doped coatings.