Some properties of platinum and palladium modified aluminide coatings deposited by CVD method on nickel-base superalloys

Abstract

In the paper some functional properties (hardness and oxidation resistance) of platinum and palladium modified aluminide coatings deposited by the CVD method onanickel-based superalloy were determined. The platinum and palladium microlayers, 3 μm thick were deposited by electroplating process. The heat treatment of electroplating microlayers was performed for 2h at the temperature 1050°C in an argon atmosphere as to increase adhesion between the coating and the substrate. The low activity CVD aluminizing process of platinum heat treated coatings 3 μm thick at the 1050°C for 8h using IonBond equipment was performed. The effects of aluminizing process were verified by the use of an optical microscope (microstructure and coating thickness);ascanning electron microscope and an energy dispersive spectroscope (chemical composition of the surface and cross-section of the modified aluminide coating). The hardness measurements on the cross-section of nonmodified and platinum or palladium modified aluminide coatings were performed. Oxidation tests of modified aluminide coatings at the 1100°C for 1000hin the air atmosphere were carried out. On the grounds of the obtained results it was found that the main phase of the platinum modified aluminide coating is β-(Ni,Pt)Al. Consequently, the palladium modification of aluminide coating causes the formation of β-(Ni,Pd)Al phase. The platinum modified aluminide coating has better oxidation resistance than nonmodified and palladium modified aluminide coating. The XRD analysis of the surface of oxidized platinum modified aluminide coating confirmed the presence of the thermodynamically stable oxide layer Al 2O3, that has good protective properties. The oxides of NiAl2O4, Al198Cr002O3 and TiO2 were found on the surface of the palladium modified aluminide coating after 1000hoxidation at the 1100°C the in the air atmosphere.