Zirconium was introduced to the aluminide coating by means of two methods: the EB-PVD method and the CVD method. Zirconium layers (1 and 3 µm thick) were deposited by the EB-PVD method on the pure nickel substrate. Than samples were aluminized by the CVD method. Aluminizing process leads to obtain triple zone coatings. The top ß-NiAl zone, the middle γ’-Ni3 Al zone and the inner γ – Ni(Al) zone were observed. Intermetallic phases NiZr(NiZr2 ) and Ni5Zr on the border between the top and the middle zone and middle zone and thesubstrate were found. When zirconium was introduced to the aluminide coating during the CVD process a triple zone coating was obtained. It was found that zirconium is dissolved in the NiAl phase.
Keyword: aluminide coatings
The paper presents comparison of microstructures of hafnium modified aluminide coatings deposited in two different ways on pure nickel. In the first way a hafnium layer was deposited by the EB-PVD method, subjected to the diffusion treatment for 6 hours and than aluminum was deposited by the CVD method. In the second method, double layers of hafnium (3 μm thick) and aluminum (3 μm thick) were 0 deposited by the EB-PVD method on the nickel substrate. The double layers were subjected to diffusion treatment at 1050 C for 6 h. The obtained coatings were examined by the use of an optical microscope (microstructure and coating thickness) and a scanning electron microscope (chemical composition on the cross-section of the modified aluminide coating). In aluminide coatings deposited by the CVD process, an outward nickel diffusion via the hafnium layer and inward aluminum diffusion to the surface of nickel lead to the formation of a diffusion zone. Hafnium forms a layer of intermatallic phases with nickel in the diffusion zone. Diffusion treatment for 6 h of nickel with hafnium and aluminum layer leads to formation of the Ni5Hf phase.