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

Abstract

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'-Ni 3 Al phase. The oxide layer (10 µm thick) consists of the NiAl 2 O 4 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-Al 2 O 3 phase and the top layer of the NiAl 2 O 4 phase. Al-depleted (30 at. %) β-NiAl grains besides the γ'-Ni 3 Al phase were found in the rhodium-modified coating, while only the γ'-Ni 3 Al 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).Wu et al. [10] introduced iridium to the aluminide coatings as a cost alternative to platinum. Firstly, the iridium layer (6 µm thick) was deposited on TMS-75 nickel-base single-crystal superalloy. Secondly, the coated superalloy was aluminized by the pack-cementation method and then cyclic oxidation tests were performed. A dense and uniform layer of the β-(Ir,Ni)Al phase was identified after aluminizing. The growth rate of oxide on Ir-Al coated superalloy was lower than on the aluminized one. Moreover, the transformation from β-NiAl phase to the γ'-phase was decelerated due to the presence of the (Ir,Ni)Al layer. The presence of iridium in the aluminide coating retarded the outward and inward diffusion of solute elements during oxidation (nickel and aluminum).The addition of 5 % wt. rhodium to the Ni-8Cr-6Al alloy increases oxide-scale adherence to the alloy and improves its oxidation resistance [11]. Rhodium addition to the aluminide coatings also increases oxidation resistance of coated alloys [12]. Therefore, rhodium-modified aluminide coatings can be an alternative for palladium-modified aluminide ones. However, there is a lack of data about comparison of the oxidation resistance of rhodium or palladium-modified aluminide coatings. That is why this paper presents comparison of the oxidation resistance of the non-modified, palladium or rhodium-modified aluminide coatings and uncoated substrate. Experimental ProcedureCMSX-4 superalloy (single-crystal) was used as a substrate material. The chemical composition of the superalloy was as follows: 61.7% wt. Ni, 6.5% wt. Cr, 9% wt. Co, 0.6% wt. Mo, 5.6% wt. Al, 1% wt. Ti, 6% wt. W, 0.1% wt. Hf, ...

The effect of precious metals in the NiAl coating on the oxidation resistance of the Inconel 713 superalloy

“…The aluminide coating with rhodium addition showed slower oxidation rate than plain aluminide and aluminide coatings with palladium addition. The better oxidation resistance of the rhodium modified aluminide coating than the palladium modified one was also found on the CMSX 4 superalloy [21]. The rhodium modified aluminide coatings may be an alternative to palladium modified ones [21].…”

“…The better oxidation resistance of the rhodium modified aluminide coating than the palladium modified one was also found on the CMSX 4 superalloy [21]. The rhodium modified aluminide coatings may be an alternative to palladium modified ones [21].…”

Optimizing microstructure and mechanical properties of NiAl-9Mo alloy by Zr addition and suction casting process

“…The requirement for materials with high-temperature performance is increasing due to the world's fast development in aerospace, energy, and other sectors, particularly in the crucial area of aerospace engines [1][2][3][4]. The NiAl alloys with a B2 structure that features a high melting point, low density, high elastic modulus, and outstanding high-temperature oxidation resistance, are the most typical of high--temperature structural materials.…”

Interdiffusion Behaviour of NiCoCrAlY Coating and N5 Single Crystal Superalloy

“…However, the huge differences in composition between coating and underlying substrate can lead to element interdiffusion during long-term high-temperature service, resulting in the segregation of insoluble elements such as Ta in the substrate and the precipitation of harmful topological close-packed 2 of 10 phase [15][16][17]. The main components of topological close-packed phases are W, Mo and Re, which are added in the superalloy for strengthening the comprehensive performance of superalloys at high temperature [18][19][20]. There is no doubt that the precipitation of harmful topological close-packed phases will not only deplete the refractory reinforcing elements in the substrate but also be the source of rack propagation, resulting in the system failure [21,22].…”