Palladium-modified aluminide coatings: Mechanisms of formation
- Universite Henri Poincare Nancy, Vandoeuvre (France)
- O.N.E.R.A. Direction Scientifique des Materiaux, Chatillon (France)
The need to increase the efficiency of turbo engines has led manufacturers to increase the temperature of gases at the exhaust of the combustion chamber. Another limiting factor for the lifetime of blades or vanes used in gas turbines is hot corrosion due to the condensation of alkaline sulfate produced by the oxidation of sulfur contained in kerosene or fuels. To overcome these problems, the use of protective coatings has come into general use. A systematic investigation of the influence of Pd-Ni predeposit alloys on the microstructure and composition of aluminum diffusion coatings has been conducted on Ni base superalloys (mainly IN738). Their metallurgical structure has been studied with a special emphasis on the nature of the phases and distribution of the various elements throughout the coating section. A two-layer structure similar to that formed on simple aluminide coatings is observed whatever the type of aluminizing treatment (low and high aluminum activity, pack of vapor-phase coating). The superficial layer is, however, very different from that observed in simple aluminide coatings, since it is constituted with a ternary PdNi aluminide. Palladium concentration profiles, which significantly differ when using low or high activity cements, and the results of a study of the ternary Ni-Pd-Al phase diagram, provide qualitative indications concerning the coatings` growth processes. Palladium, if present at a sufficient level, enhances Al diffusion in the beta phase. In the case of low activity processes, a consequence of this increase of Al diffusion flux is the location of an NiAl reaction zone inside the coating.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 61506
- Journal Information:
- Journal of the Electrochemical Society, Vol. 142, Issue 2; Other Information: PBD: Feb 1995
- Country of Publication:
- United States
- Language:
- English
Similar Records
Pack cementation aluminide coatings on superalloys: codeposition of Cr and reactive elements
High Temperature Oxidation Performance of Aluminide Coatings