Preparation of Ni-Al-Pt Coating on Ni-6 at%Cr Alloy by Electrodeposition Method and Cyclic-Oxidation Resistance

Abstract

The formation of a coating layer consisting of Ni, Al and Pt on a Ni-6 at% Cr alloy substrate was attempted by the electrodeposition of Pt and Al. The Pt and Al were deposited by electrolysis in an aqueous solution and molten salt, respectively. The cyclic oxidation resistance of the alloy with this coating was then evaluated in air at 1423 K. Particular attention has been paid to the effects of Pt in the coating and 6 at% Cr in the alloy substrate on the cyclic oxidation resistance. For the sample treated by Pt deposition, followed by the Al deposition, a coating layer comprised of an outer layer consisting of PtAl 2 and Ni 2 Al 3 and an inner layer consisting of Ni 2 Al 3 was formed. This coating layer contained about 2 at% Cr. The cyclic oxidation test showed that for the sample with a coating consisting of Ni aluminide without Pt, a mass reduction due to spallation of an oxide scale took place during the oxidation test, whereas for the sample with a coating consisting of Ni aluminide containing Pt, no mass reduction took place. For the sample with a coating consisting of Ni aluminide containing Pt after the oxidation test, the formation of an adhesive Al 2 O 3 scale was observed. The cyclic oxidation test also showed that for the sample with a coating consisting of Ni aluminide containing Pt formed on a pure Ni substrate, a large mass increase took place during the oxidation test, while for the sample with the coating formed on the Ni-6 at% Cr alloy substrate, such a mass increase did not take place. Such effects of Pt in the coating and 6 at% Cr in the alloy substrate on the cyclic oxidation resistance are discussed from the viewpoint of the formation of a protective Al 2 O 3 scale.

Experimentally investigation of the high temperature oxidation mechanism for Ni-Al-Pt alloy supported by CALPHAD calculations

“…The Pt-modi ed γ + γ′ two-phase Ni-based alloys [3][4][5][6] as a new generation of bond coat have been widely reported for its excellent properties, especially for the up-diffusion effect of Al, which can ensure the su cient Al delivering from the superalloy substrate. The in uence of Pt on the metal/oxide interface during high temperature oxidation have been extensively investigated by the researchers [7][8][9][10], Pt can inhibit the formation of void and limit the outward diffusion of other alloy elements from the substrate, thus prevent the generation of undesirable oxide around the interface between the α-Al 2 O 3 and substrate. Furthermore, Pt can also improve the oxidation resistance by diminishing the chemical activity of Al [11].…”