Synergistic effect of Pd+Rh on the microstructure and oxidation resistance of aluminide coatings

Abstract

The Pd+Rh modified aluminide coatings were deposited on nickel and CMSX-4 nickel superalloy. The Pd layer (2.5 μm thick) and the subsequent Rh layer (0.5 μm thick) were electroplated on both nickel and CMSX-4. The aluminization of the substrates with Pd+Rh layers was carried out using the CVD method. Two zones (outer and interdiffusing) were observed on both coatings. The β-NiAl phase doped in palladium was formed in the outer zones and β-NiAl phase doped with palladium and rhodium was formed at the boundary between the outer and interdiffusion zones of both coatings. The γ’- Ni3Al phase and μ-Co7Mo6 precipitates in the β-NiAl matrix were found in the interdiffusion zone on nickel and CMSX-4 superalloy respectively. The simultaneous use of Pd and Rh in the aluminide coating slowed down their oxidation rate. Moreover, Pd+Rh co-doping is more efficient than Pd+Hf in reducing the oxidation rate of aluminide coating on CMSX-4 superalloy.

Keywords

• pd+rh
• aluminide coating
• oxidation
• kp value