Cold Spray MCrAlY Coatings on Single-Crystal Ni-base Superalloys: A Substrate Perspective

The hot-section components of modern gas turbines (e.g., turbine blades and vanes) are typically manufactured from Ni-base superalloys. To develop γ/γ’ microstructure that imparts superior thermomechanical and creep properties, Ni-base superalloys usually require three distinct heat treatments: first a solution heat treatment (SHT), followed by primary ageing (PA), and finally secondary ageing (SA). To achieve oxidation resistance, MCrAlY coatings are applied on the superalloy components as either environmental coatings or bond coats for thermal barrier coatings. In this study, the effects of different processing sequences on cold spray (CS) MCrAlY coating characteristics and short-term isothermal oxidation performance were investigated. Specifically, three processing sequences were carried out with CS NiCoCrAlTaY coatings deposited on CMSX-4 single-crystal Ni-base superalloy substrates that underwent SHT, SHT+PA, and SHT+PA+SA, respectively. The missing heat treatments for the first two superalloy substrates were then performed on the coated samples after CS deposition. The microstructures of the CMSX-4 substrates and CS NiCoCrAlTaY coatings were characterized after each step. Isothermal oxidation performance of the coated samples following different sequences was evaluated at 1100°C for 2 hours. The results demonstrated that superalloy ageing heat treatments could potentially be used to homogenize coating microstructure and improve the oxidation performance of MCrAlY coatings.