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

Abstract

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 β-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 µm while the average thickness of the outer β-NiAl zone was about 35 µm. 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

Microstructure of Aluminide Coatings Modified by Pt, Pd, Zr and Hf Formed in Low-Activity CVD Process

“…It might be connected with some concentration of this element from base alloy. According to our previous results [18], the formation of small precipitations containing Zr was observed in Pd/Zr modified aluminide coatings. The presence of small Zr-precipitations was confirmed by Yavorska et al [28] The concentration of Pd in (Pd + Hf)-Al (5) coating was similar to that measured in Pd-only modified coating.…”

“…Reactive elements, such as Hf, can improve oxidation resistance of aluminide coatings. Pytel et al [18] used the CVD low-activity process for doping by Hf produced in an external generator.…”

“…Based on a conducted review as well as our previous works [6,18], the doping of aluminide coatings by Pt/Pd, as well as Hf or Pd using industrial processes, was tested. The different combinations of doping elements were tested and their influence on chemical composition of coatings was initially investigated.…”

Progress in Novel Electrodeposited Bond Coats for Thermal Barrier Coating Systems

“…Research attempts were also made by performing electrodeposition of different combinations of metals followed by addition of rare earths (such as Zr [ 44 , 47 ], Hf [ 4 , 48 ], and Ce; and their oxides) [ 49 ]. The incorporation of all the above-mentioned elements (Pt, Pd, Zr, Hf) and their combination through electroplating followed by diffusion aluminising was demonstrated to influence the oxidation resistance of aluminide coatings positively.…”

“…Though diffusion aluminide coatings were extensively studied using an intermediate electroplated layer (Pt, Pd, Pt + Pd) with or without reactive element (Zr, Hf) doping, they still suffer from certain drawbacks, such as rumpling/wrinkling tendency of the grown oxide layers, spallation of ceramic top coat, prone to cracking and so on [ 4 , 8 , 34 , 35 , 44 , 47 , 50 ]. Subsequently, focus has been shifted to the development of MCrAlY overlay coatings (M = Ni, Co, or Ni + Co) as they offer superior mechanical properties, flexibility in terms of composition selection, and facilitate creation of coatings with balanced combinations of coating properties.…”