SEM/TEM investigation of aluminide coating Co-doped with Pt and Hf deposited on Inconel 625

The effect of simultaneous introduction of Hf and Pt into aluminide coating deposited on Inconel 625 alloy was investigated using scanning and transmission electron microscopy (SEM/TEM) methods. The coating consisted of two layers: the additive and the interdiffusion. The additive layer and part of the interdiffusion layer consist of the β-NiAl type phase. The middle part of the interdiffusion layer comprised an interpenetrating finger-like structure formed by the β-NiAl and TCP-σ type phases with numerous fine Cr precipitates in the former and occasional larger precipitates of NbC carbides interspersed in between them. The σ type phase inclusions are situated at the border between the substrate and the interdiffusion layer. The experiment showed that platinum fully dissolves in the β-NiAl-type matrix, while most of the introduced hafnium accumulates in HfO2 dioxide precipitates located close to the additive/interdifusion interface

Oxidation Behavior of Non-Modified and Rhodium- or Palladium-Modified Aluminide Coatings Deposited on CMSX-4 Superalloy

Rhodium-modified as well as palladium-modified and non-modified aluminide coatings on CMSX-4 Ni-based superalloy were oxidized in air atmosphere at 1100 °C. Uncoated substrate of CMSX-4 superalloy was also oxidized. The microstructure of coatings before oxidation consists of two layers: an additive and an interdiffusion one. The NiAl intermetallic phase was found in the microstructure of non-modified coatings, while the (Ni,Rh)Al intermetallic phase was observed in the microstructure of rhodium-modified aluminide coatings before oxidation. The (Ni,Pd)Al phase of palladium-modified aluminide coatings in the additive layer was observed before oxidation. The microstructure of the oxidized non-modified coatings consists of the γ’-Ni3Al phase. The oxide layer (10 µm thick) consists of the NiAl2O4 phase and porous Ni-rich oxide. The oxide layers (5 µm thick) formed on the surface of rhodium or palladium-modified coatings consist of the α-Al2O3 phase and the top layer of the NiAl2O4 phase. Al-depleted (30 at. %) β-NiAl grains besides the γ’-Ni3Al phase were found in the rhodium-modified coating, while only the γ’-Ni3Al phase region was revealed in the palladium-modified coating, Rhodium-modified coatings with small rhodium content (0.5 µm rhodium layer thick) can be an alternative for palladium-modified ones with bigger palladium content (3 µm thick palladium layer)

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

Pd + Zr co-doped aluminide coatings were deposited on the CMSX-4 nickel superalloy, widely used in the aircraft industry, in order to investigate their microstructure and improvement of oxidation resistance. Palladium was deposited by the electrochemical method, whereas zirconium and aluminum by the chemical vapor deposition (CVD) method. Coatings consist of two zones: the additive and the interdiffusion one. The additive zone contains β–(Ni,Pd)Al phase with some zirconium-rich precipitates close to the coating’s surface, whereas the interdiffusion zone consists of the same β–(Ni,Pd)Al phase with inclusions of refractory elements that diffused from the substrate, so called topologically closed-packed phases. Palladium dissolves in the β–NiAl phase and β–(Ni,Pd)Al phase is being formed. Pd + Zr co-doping improved the oxidation resistance of analysed coatings better than Pd mono-doping. Mechanisms responsible for this phenomenon and the synergistic effect of palladium and zirconium are discussed

Rhodium and Hafnium Influence on the Microstructure, Phase Composition, and Oxidation Resistance of Aluminide Coatings

A 0.5 μm thick layer of rhodium was deposited on the CMSX 4 superalloy by the electroplating method. The rhodium-coated superalloy was hafnized and aluminized or only aluminized using the Chemical vapour deposition method. A comparison was made of the microstructure, phase composition, and oxidation resistance of three aluminide coatings: nonmodified (a), rhodium-modified (b), and rhodium- and hafnium-modified (c). All three coatings consisted of two layers: the additive layer and the interdiffusion layer. Rhodium-doped (rhodium- and hafnium-doped) β-NiAl phase was found in the additive layer of the rhodium-modified (rhodium- and hafnium-modified) aluminide coating. Topologically Closed-Pack (μ and σ) phases precipitated in the matrix of the interdiffusion layer. Rhodium also dissolved in the β-NiAl phase between the additive and interdiffusion layers, whereas Hf-rich particles precipitated in the (Ni,Rh)Al phase at the additive/interdiffusion layer interface in the rhodium- and hafnium-modified coating (c). The rhodium-modified aluminide coating (b) has better oxidation resistance than the nonmodified one (a), whereas the rhodium- and hafnium-modified aluminide coating (c) has better oxidation resistance than the rhodium-modified (b) and nonmodified (a) ones

Oxidation Resistance of Modified Aluminide Coatings

The application of protective aluminide coatings is an effective way to increase the oxidation resistance of the treated parts and prolongs their lifetime. The addition of small amount of noble metals (platinum or palladium) or reactive elements such as: hafnium, zirconium, yttrium and cerium has a beneficial effect on oxidation behavior. This beneficial effect includes an improvement of adhesion of alumina scales and reduction of oxide scale growth rate. Platinum and hafnium or zirconium modified aluminide coating were deposited on pure nickel using the electroplating and CVD methods. The coatings consisted of two layers: an outer, β-NiAl phase and the interdiffusion γ’-Ni3Al phase. Palladium dissolved in the whole coating, whereas hafnium and zirconium formed inclusions on the border of the layers. Samples were subjected to cyclic oxidation test at 1100 °C for 200h. Oxidation resistance of the palladium, Hf+Pd and Zr+Pd modified coatings deposited on pure nickel does not differ significantly, but is better than the oxidation resistance of the non-modified one

Zirconium Modified Aluminide Coatings Obtained by the CVD and PVD Methods

Universidad Autónoma del Carib