Improved oxidation resistance of AIP NiCrAlYSi coatings by applying positive bias

Abstract

The NiCrAlYSi coatings with a bias voltage of −30 V (N-coating) and + 5 V (P-coating) applied on the DD6 superalloy substrate were prepared by arc ion plating (AIP). The microstructure evolution and the oxidation resistance at 1100 °C of the two coatings were investigated. The results show that the positive bias could maintain the Al content from the target material through to the coating by enhancing droplet deposition proportion and resulting in better oxidation resistance. The as-deposited P-coating consists of γ-Ni, γ’-Ni3Al and α-Cr phases with significantly lower pores and ~ 1.1 wt% higher Al content than N-coating. The larger size (1.5 to 3.5 μm) block β-NiAl grains formed within P-coating after annealing at 1050 °C for 2 h, while it was not found in the N-coating. The oxidation parabolic rate constant at 1100 °C of annealed P-coating was confirmed as 3.54 × 10−3 mg2/(cm4·h), ~ 27.6 % lower than N-coating.