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

Abstract

The hot-section components of modern gas turbines (e.g.; turbine blades and vanes) are typically manufactured from Nibase superalloys. To develop the γ/γ' microstructure that imparts superior thermomechanical and creep properties; Nibase superalloys usually require three distinct heat treatments: first a solution heat treatment; followed by primary aging; and finally secondary aging. 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 MCrAlY coating characteristics and short-term isothermal oxidation performance were investigated. Specifically; cold spray deposition of NiCoCrAlTaY coatings was carried out on single-crystal Ni-base superalloy substrates that underwent various degrees of the full heat treatments prior to being coated. The remaining required heat treatments for the superalloy substrates were then performed on the coated samples after the cold spray deposition. The microstructures of the CMSX-4 substrates and NiCoCrAlTaY coatings were characterized after each heat treatment. Isothermal oxidation performance of the coated samples prepared using different sequences was evaluated at 1100°C for 2 hours. The results suggested a promising procedure of performing only solution heat treatment on the superalloy substrate before coating deposition and then primary aging and secondary aging on the coated samples. This processing sequence could potentially improve the oxidation performance of MCrAlY coatings; as the aging processes can be used to effectively homogenize coating microstructure and promote a thin thermally grown oxide (TGO) scale prior to actual isothermal oxidation.