High vacuum arc ion plating NiCrAlY coatings: Bias effect and approach to preparation of functional gradient coatings

The substrate bias effects on high vacuum arc ion plating (HV-AIP) of NiCrAlY coatings on superalloy were investigated at the vacuum level of 10− 3-10− 4 Pa, which are 2-3 orders in magnitude better than that of conventional low vacuum arc ion plating (LV-AIP). The negative bias applied to the substrate was in the range of − 50 V to − 450 V. Microstructures, deposition rates, and chemical compositions of the coatings are significantly influenced by the negative bias. Except for commonly observed bias induced densification in microstructure and decrease in deposition rate, strong preferential sputtering effect at high bias was observed. The sputtering yield for Cr was estimated to be ranged from ~ 0.1 to ~ 0.2 at bias from − 50 V to − 450 V, while those for Ni and Al were from ~ 0.1 to 1.5. As a result, the major phase constitution of the coatings changed from γ-Ni/γ′-Ni3Al phases at bias of − 50 V to α-Cr phase at bias of − 450 V. Such stronger preferential sputtering effect in HV-AIP fosters a strategy for preparing compositionally gradient NiCrAlY coatings just by control of the substrate bias without the need of further treatments or multi-targets. Based on this concept, preparation of several types of gradient NiCrAlY coatings with great flexibilities by one target and one process was demonstrated.