Melt spinning as a microstructural analogue for aluminide diffusion coating

Abstract

The feasibility of using melt spinning, of a high alloy nickel aluminide, as a microstructural analogue for aluminide diffusion coated nickel base superalloys is investigated in this paper. Transmission electron microscopy studies are used to characterize the relationship between coating and melt spun analogue microstructures. Attention is focused on three phases that are of principal importance in coating mechanical properties, namely: the B2 type β phase coating matrix, L1₂ type γ′ precipitates and M ₂₃ X ₆ carbides.

The microstructure of the β matrix of the melt spun analogue is shown to closely resemble that of the coating. Evidence is presented that the formation of γ′ in the melt spun alloy generally occurs in a similar manner to that in the coating. The formation of M ₂₃ X ₆ in close association with γ′ in the melt spun materials is compared to similar events in the coatings. Limitations in the ability of the melt spun materials to recreate the microstructures resulting from incorporation of substrate M ₂₃ X ₆ into the coating and formation of M ₂₃ X ₆ within β precursor phases are discussed.