The Rhodium and Hafnium Co-Doping of Aluminide Coatings on Nickel and Superalloy

Rhodium- and hafnium-co-doped aluminide coatings were manufactured via rhodium plating and further hafnizing combined with aluminizing on nickel and the CMSX-4 substrate using the Chemical Vapor Deposition CVD technique. Both co-doped coatings comprised two layers: an additive layer and an interdiffusion one. The additive layer contained the rhodium- and hafnium-doped β-NiAl phase. The interdiffusion layer on nickel contained the hafnium-doped γ’-Ni3Al phase, whereas that on the superalloy substrate contained the rhodium-doped β-NiAl phase. The chain of the hafnium-rich small particles was formed near the additive/interdiffusion layer border on both substrates. Rhodium- and hafnium-co-doped intermetallic coatings showed improved oxidation resistance compared to those doped only with rhodium. Moreover, rhodium and hafnium co-doping is more efficient than palladium and hafnium co-doping in reducing the oxidation rate of the aluminide compound on the CMSX-4 substrate.