Oxidation Behavior and Oxide Transformation of a Pt-Modified Aluminide Coating at Moderate High Temperature

Abstract

The oxidation performance of a single-phase Pt-modified aluminide coating was assessed in oxidation test at 980 °C in comparison with the single crystal superalloy. The results suggested that the Pt-modified aluminide coating exhibited superior oxidation resistance. During oxidation, the oxide scale formed on bare alloy changed constantly followed by the constitution of the multi-layer scale structure: An outer scale mainly consisted of Cr2O3 + NiCr2O4 + TiO2 with scarce protection, and an internal scale mainly consisted of Al2O3. The thickness of the outer oxide scale increased with time, where the scale became looser and more porous. Meanwhile, the internal scale was discontinuous. Oxygen and nitrogen inwardly diffused into substrate, forming Ta2O5 and TiN particles. In contrast to the complex constitution of oxide scale, a uniform and continuous Al2O3 scale formed on Pt-modified aluminide-coated samples after oxidation at 980 °C for 1500 h, which showed no spallation and cracking. Interestingly, θ-Al2O3 and α-Al2O3 phases remained after such a long oxidation time. It is the relatively lower temperature and the presence of Pt retarded θ-α transformation. The degradation rate from β-NiAl to γ′-Ni3Al was very slow in the coating. The various development of oxide scale on the coating and substrate was individually studied.

The Influence of Pd and Zr Co-Doping on the Microstructure and Oxidation Resistance of Aluminide Coatings on the CMSX-4 Nickel Superalloy

“…Therefore, the bondcoat, situated between the ceramic topcoat and the substrate, must be oxidation resistant. Moreover, it ensures top coating's good adhesion and mitigates thermal mismatch stresses [4]. The most popular bondcoats are MCrAlY ones (M denotes Ni and/or Co) and aluminide coatings.…”

“…The modification of aluminide coatings by noble metals, like palladium [11] or platinum [12], reduces the oxide scale growth rate and improves their adherence to the substrate, as well as delays β to γ phase transformation. The addition of noble metals significantly slows down the diffusion of refractory alloying elements from the substrate eliminating formation of chromium-rich inclusions in the outer layer of the coating [4]. Main phases in modified coatings deposited on CMSX-4 and Inconel 713 LC nickel-based superalloys are: (Ni,Pd)Al or (Ni,Pt)Al, respectively.…”

“…As the creep resistance of CMSX-4 nickel superalloy is good, it is widely used in the aircraft industry, e.g., on turbine blades that are exposed to high temperatures and aggressive environments in the hot section of aircraft engines. Unfortunately, the oxidation resistance of this alloy is rather poor, and therefore finding a protective coating that would improve oxidation resistance of CMXS-4 superalloys is very important, because this way the lifetime of aircraft engines could be prolonged [4]. So far, the authors of this paper have analyzed the influence of several modifiers, e.g., Pd [4] or Pd + Hf [24], and observed that the modifiers mentioned above improve the oxidation resistance of coatings and that co-doping is more effective than mono-doping.…”

Selective Oxidation of the Intermetallic Compound PtAl2 from Ab Initio Thermodynamics

“…Aluminide coatings have been widely used in the aerospace industries for the protection of the hot-section components of gas turbines against oxidation since the late 1960s. − The excellent oxidation resistance of aluminide coatings mainly depends on the formation of a compact, continuous, and adherent Al 2 O 3 film to inhibit continued oxidation of the substrate alloy under the high-temperature environment. To fulfill the requirements of higher temperatures of the inlet gas in modern turbines, aluminide coatings are usually modified by adding various modification elements, such as Pt, − Hf, − Co, − Si, Pd, , Y, and Dy . It is widely accepted that the addition of Pt can improve the oxidation resistance and stabilize the phase constitution of the aluminide coatings, which entitles Pt-modified aluminide coatings as one of the most used bond coats in the thermal barrier coating system (TBCs). , The Pt-modified aluminide coatings are mainly composed of PtAl 2 , β-(Ni,Pt)­Al, and γ-Ni/γ′-Ni 3 Al, where γ and γ′ refer to the Ni­(Al) substitutional solid solution with the face-centered cubic (FCC) lattice and a random distribution of Ni and Al atoms and the L1 2 -ordered Ni 3 Al intermetallic compound, respectively.…”

Investigation on Optimal Ta/Cr Ratio of a Single Crystal Ni-Base Superalloy in View of the Isothermal Oxidation Behavior

“…Cr is one of the most important elements for superalloys to resist oxidation attacks. Sufficient Cr promotes the formation of a continuous and adherent Cr 2 O 3 scale on the surface of the alloy [15,16]. The diffusion rate of ions through the Cr 2 O 3 scale is extremely slow.…”