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

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 NiAl3, with small amounts of Fe2Al5 and CrAl5. 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.