Preparation of a Duplex Nanocrystalline Coating by Magnetron Sputtering and Its Oxidation Performance

A duplex nanocrystalline coating was prepared in this study by magnetron sputtering on N5 single-crystal super alloy (Ni: Bal, Co: 7.5, Cr: 7.0, Al: 6.2, Ta: 6.5, Re: 3.0, Mo: 1.5 and W: 5.0, wt%). The novel nanocrystalline coating consists of two layers, the inner layer having the same composition with the alloy substrate for avoiding elements inter diffusion while the outer layer has 7.6 wt% higher Al to quickly ensure the formation of a protective Al₂O₃ layer. Both two layers were deposited within one magnetron sputtering apparatus that contained two targets. The main target was having the same alloy substrate in composition and secondary target with pure Al. The difference in Al content between the two layers was achieved by controlling the secondary target during sputtering. This study revealed a way for preparing a series of similar coatings with varying compositions and improving performance. After oxidation at 1050 °C, a protective Al₂O₃ layer was quickly formed on the duplex nanocrystalline coating and no TCP phases were detected in the alloy substrate.