Nanoparticles in zirconium-doped aluminide coatings

Abstract

a b s t r a c tThe microstructure of the zirconium doped aluminide coating deposited on the nickel substrate by the CVD method is presented. TEM analysis proved that the ß-NiAl and the γ 0 -Ni3Al are the main phases of the deposited coating. Some dislocations in the nickel substrate and in the coating were observed. The cross section chemical composition examination revealed, that the coating was formed via the inward aluminum diffusion and the outward nickel diffusion. SEM analysis revealed small zirconium content (0.2-0.4 at%) on the cross-section of the aluminide coating. Such zirconium content leads to zirconium dissolution in the aluminide coating. Long time of zirconizing (4 h) caused the appearance of zirconium nano particles at the surface of the coating. TEM investigations confirmed that zirconium formed inclusions on the coating's surface.

Nanoparticles in hafnium-doped aluminide coatings

“…Simultaneously, no Hfrich inclusions nor intermetallic phases like for instance Hf 3 Ni 7 , HfNi 3 , Hf 2 Ni 7 or Ni 2 AlHf, suggested by other authors [17,26] were noted. Similar results have been obtained for zirconium modified aluminide coatings deposited on pure nickel by the CVD method [32]. Also in that case only Zr phase (heksagonal structure with cell parameters: a¼ 3.232 nm and c¼ 5.147 nm) precipitates were found.…”

“…Also in that case only Zr phase (heksagonal structure with cell parameters: a¼ 3.232 nm and c¼ 5.147 nm) precipitates were found. Zirconium particles were found along grain boundaries at the top surface of the β-NiAl phase [32], whereas hafnium inclusions, observed in the present research are predominantly distributed uniformly inside the β-NiAl phase grains with only occasional presence of such precipitates at the β-NiAl grain boundaries.…”

Preparation and Isothermal Oxidation Behavior of Zr-Doped, Pt-Modified Aluminide Coating Prepared by a Hybrid Process

“…The solubility of the Zr element in the NiAl phase is still unknown, but the diameter of the zirconium atom is much larger than the interplanar spacings of the β-NiAl phase, so it is hard to dissolve much Zr in the NiAl phase. It is estimated that 0.2-0.4 at.% Zr could be dissolved in the aluminide coating [6]. Some research showed that Zr tended to segregate around the NiAl grain boundary as Zr particles or combine with other elements in the form of compounds like Ni7Zr2, NiAl-Zr, or Al5Ni2Zr, etc.…”

“…Also, there is less β phase transformed into γ' phase in the Zr-doped, Pt-modified aluminide coating, which means that less compressive stress would be formed in the coating and scale. In addition, Zr is reported to aid in increasing the creep resistance and lowering the internal stress [6]. When the internal stress in the alumina layer is too high, it will lead to crack and even spallation of the alumina scale.…”

“…However, there are still voids formed at the metal/oxide interface at high temperature, which accelerate the degradation of the coating [6]. It is…”