Microstructure evolution and oxidation behavior of silicon-modified aluminide coatings on IN718 superalloy at 1000 °C

Abstract

Due to the increased service temperature of turbine blades, the high temperature conditions seriously deteriorate the mechanical properties of nickel-based superalloys, thus it is necessary to prepare the anti-oxidation coating. This research investigated the microstructure evolutions and oxidation behaviors of simple and silicon-modified aluminide coatings at 1000 °C for 200 h. After oxidation, serious spalling out and failure appeared due to spinal NiCr₂O₄ and volatile Cr₃O phase formation in the IN718 superalloy. For the aluminide coating, the formation of stable α-Al₂O₃ oxide film significantly improved the oxidation resistance, with a mass gain of only 0.1 mg/cm² during the oxidation of 100–200 h. The silicon-modified aluminide coating exhibited the lowest mass gain, rapidly formed stable SiO₂ oxide film due to the existence of the Cr_9.1Si_0.9 phase and maximum grain size in the external coating, and the internal Al₂O₃ oxide together with the coating formed the pinning effect, effectively preventing the delamination of the oxide film. However, the formation and growth of the Ni₃Si phase generated microcracks, leading to its rate of mass gain surpassing that of aluminide coating during oxidation of 100–200 h, which illustrates that effectively regulating the Si content is imperative to prolonging the service life of turbine blades.