Microstructure and Oxidation Behavior of Pt and Pt–Ir Diffusion Coatings on Ni-Based Single Crystal Superalloy

抄録

The effects of Ir addition and coating method on the microstructure and oxidation behavior of Pt–xIr (x = 0–30 at%) diffusion coatings were investigated. A nickel-based single crystal superalloy UCSX-8 was used as a substrate material, while the coatings were developed by either an electroplating or a paste coating method followed by an annealing heat treatment. The phase identification and microstructure analyses by XRD and SEM/EDS revealed that the alloying of Ir in Pt diffusion coating resulted in the formation of L1₀ ordered α-NiPt₂Al structure. Cyclic oxidation tests were carried out at 1423 K in still air in order to investigate the thermal stability and oxidation behavior of the coatings. It was found that Ir can significantly retard the formation of voids in both the coating and substrate. In addition, by replacing electroplating method to the paste coating method, the crack problem due to the brittle feature of electroplated Pt–Ir coatings could be solved. Therefore, the Pt–20Ir diffusion coating prepared by the paste-coating method is promising as the bond-coating material due to formation of less voids, no crack and stable Al₂O₃ on the surface.

Fig. 5 Oxidation kinetic curve of the specimens during cyclic oxidation test at 1423 K.