Nanoparticles in hafnium-doped aluminide coatings

• The hafnium distribution was investigated by the transmission electron microscopy.
• The coating consists of the γ′-Ni3Al and the β-NiAl phases.
• Hafnium precipitates inside β-NiAl grains as nanoparticles less than 50 nm.
• Hafnium formed precipitates of the Hf phase (hexagonal structure).
• No other Hf-rich inclusions suggested by other authors were note.

The microstructure of the hafnium modified aluminide coating deposited in the CVD process on pure nickel was analyzed using a TEM method. The coating was formed through the nickel outward diffusion from the substrate and the aluminum inward diffusion from the surface. It consisted of the β-NiAl and γ′-Ni3Al layers formed near surface and substrate, respectively. The Kirkendall-like porosity corresponding to the location of initial surface of the substrate was observed within the β-NiAl phase, but close to the interface with the γ′-Ni3Al phase. Hafnium tends to accumulate in nanoparticles distributed in the upper layer of the β-NiAl phase.