Synthesis of Hf-modified aluminide coatings on Ni-base superalloys

With small additions of Reactive Elements (RE), such as hafnium (Hf), to aluminide coatings applied on aircraft turbine engine components, the adherence of the protective oxide scale to the coatings and the oxidation resistance of the coatings at high temperatures can be significantly improved. At SIFCO, Hf-modified aluminide coatings, Hf–Pt-modified aluminide coatings on Ni-base superalloys and the industrial-scale production of Hf-modified aluminide coatings on different aircraft turbine engine components were successfully developed. Surface morphology and cross-section microstructure of the developed coatings were inspected and compared by using a Scanning Electron Microscope (SEM) equipped with energy dispersive spectroscopy (EDS), and Glow-Discharge Mass Spectrometry (GDMS). Experimental results showed that Hf was successfully incorporated and precipitated Hf-rich particles were observed on the coating surface, along grain boundaries within the additive layer, and at the interface between the additive layer and the interdiffusion layer. Finally, Hf-rich particles as well as Hf solubility are discussed.

► Successful development of low content Hf-modified aluminide coatings on pure Ni and Ni-base superalloy coupons.
► Successful industrial-scale production of Hf-modified aluminide coatings on Ni-base superalloy turbine engine components.
► Discussion about Hf-rich particles formed on the surface, grain boundaries and interface.
► Discussion about Hf solubility limit in NiAl coating phase.