Microstructure and oxidation behavior of NiCoCrAl/YSZ microlaminates produced by EB-PVD

Two NiCoCrAl/ZrO₂-Y₂O₃ microlaminates (A and B) were fabricated by electron beam physical vapor deposition, which were different in layer number and metal-layer thickness. The layer number was 20 and 26, respectively. And the metal-layer thickness was 35 and 14 μm, respectively. The microstructure and isothermal oxidation behavior were investigated. During the exposure in air at 1000 °C for 100 h, the t to m phase transformation occurred in the ceramic layers, and oxide scales formed at the surfaces of not only the outer metal-layers but also the internal metal-layers for the microlaminates. The oxidation rate of microlaminate B was greater than that of microlaminate A. Their overall mass gains were significantly dependent on the number and thickness of the metal-layers. The oxidation products were also influenced by metal-layer thickness. Oxide scales of the 35 μm thick metal-layer microlaminate (A) consisted mainly of α-Al₂O₃ and θ-Al₂O₃, while the oxidation products of the 14 μm thick metal-layer microlaminate (B) were the mixture of α-Al₂O₃, θ-Al ₂O₃ and Cr₂O₃. It was also found that the growth of the oxide scale adjacent to the top YSZ layer was controlled by the oxygen diffusion, and that the growth of the oxide scale adjacent to the internal YSZ layer was controlled by the metal ionic diffusion.