Structure of Pd-Zr and Pt-Zr modified aluminide coatings deposited by a CVD method on nickel superalloys

In this paper, the structure of newly developed modified aluminide coatings is characterized. The platinum and palladium coatings were obtained by an electroplating process. The Pt and Pd electroplated samples were aluminized and also modified by zirconium doping during the CVD (Chemical Vapour Deposition) low-activity process. Aluminide coatings were deposited using industrial CVD system. In the paper, the process parameters are described as well as the results of the microstructural analysis. The chemical and microstructure analysis was conducted using electron microscopes equipped with an energy dispersive spectrometer attachment. The phase composition analysis was performed using an X-ray diffractometer and showed that the aluminide coatings (Pt-Zr and Pd-Zr modified) obtained by CVD low-activity aluminizing comprised beta-NiAl phase grains enriched in platinum (max. approx. 16 at.% of Pt) or palladium (max. approx. 21 at.% of Pd). The coatings consisted of two or three zones. The first outer zone was a single phase - (Ni,Pt/Pd)Al type. The aluminium-content of the outer zone of the platinum modified aluminide coating was approx. 45 at.%, while aluminiumcontent in the outer zone of the palladium modified aluminide coatings was approx. 52 at.%. The results showed that the total thickness of aluminide coatings was an average of about 50 mu m while the average thickness of the outer beta-NiAl zone was about 35 mu m. These types of aluminide coating are applied to the thermal barrier coatings with a ceramic outer layer produced by EB-PVD (electron beam physical vapour deposition) or hybrid LPPS-PS PVD (Low-Pressure Plasma PS-PVD) methods.