Low-temperature formation and oxidation resistance of ultrafine aluminide coatings on Ni-base superalloy

Abstract

Ultrafine aluminide coatings were successfully produced on Ni–18Fe–17Cr superalloy at 540–600 °C in a modified pack-aluminizing process. Repeated ball-impacts accelerated the formation of the aluminide coatings by a surface refining process, resulting in atomic diffusion occurring at a relatively low temperature. The effects of the operation temperature and the treatment duration on the formation of the coatings have been investigated. The coatings possessed a two-layer structure. The top layer, approximately 5 µm in thickness, exhibited equiaxial coarse grains and was dominated by NiAl 3, with small amounts of Fe 2Al 5 and CrAl 5. The bottom layer showed high density, homogeneous, ultrafine grains with diameters approximately 30–50 nm. High-temperature oxidation tests were carried out at 1000 °C. The oxidation kinetics and microstructure of the oxide scale were studied. The experimental results indicated that the coatings greatly enhanced the high-temperature oxidation resistance of Ni–18Fe–17Cr superalloy.