Microstructural study of aluminide surface coatings on single crystal nickel base superalloy substrates

Gale, W.F. and King, J.E. (1992). Microstructural study of aluminide surface coatings on single crystal nickel base superalloy substrates. Materials Science and Technology, 8 (8), pp. 673-678.

Abstract

Aluminide diffusion coatings are frequently employed to enhance the oxidation resistance of nickel base superalloys. However, there is a concern that the presence of an aluminide coating could influence the properties of the coated superalloy, especially in respect of fatigue behaviour. To understand the nature of the effects of surface coatings on the fatigue properties of superalloys, an understanding of microstructural development within both the coating and the coating/substrate interfacial zone during high temperature fatigue testing is necessary. This paper is concerned with microstructural changes in aluminide diffusion coatings on single crystal γ′ strengthened superalloy substrates during the course of high temperature fatigue testing. The 'edge on' transmission electron microscopy technique is employed to study cross-sections of two stage (aluminization plus diffusion treatment) coated superalloy samples. The paper examines the degradation of the coating produced by phase transformations induced by loss of aluminum from the coating and/or aging of the coating. Aluminum removal both by interdiffusion with the substrate and by oxidation of the coating surface is considered. Microstructural development in the portion of the substrate influenced by interdiffusion with the coating is also discussed.

Divisions: Aston University (General)
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Uncontrolled Keywords: aluminum,crystals,degradation,diffusion,fatigue of materials,high temperature testing,interfaces (materials),microstructure,nickel alloys,oxidation,phase transitions,superalloys,aluminide surface coatings,edge on transmission electron microscopy,nickel based superalloy substrates,diffusion coatings,Materials Science(all),Metals and Alloys
Published Date: 1992-08

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