Cold spray for production of in-situ nanocrystalline MCrAlY coatings – Part I: Process analysis and microstructure characterization

Abstract

Nanocrystalline MCrAlY coatings have been shown excellent oxidation performance as bond coats in thermal barrier coating (TBC) systems. In the first part of the present study, a cold spray (CS) process is proposed, aiming at producing in-situ nanocrystalline NiCoCrAlTaY coatings on CMSX-4 single-crystal Ni-base superalloy substrates while using conventional powders of large grain sizes. Scanning electron microscopy (SEM), scanning transmission electron microscopy (STEM), and X-ray diffraction (XRD) were used to characterize the resulting coating-substrate system. Results show that the feedstock powder particles experienced substantial plastic deformation, which promoted dynamic recrystallization and grain refinement resulting in extended nanostructures in the CS NiCoCrAlTaY coatings. Furthermore, interfacial features such as materials mixing and intimate metal-metal contacts without pores or oxide fragments suggest the presence of mechanical and potentially metallurgical bonding between the CS NiCoCrAlTaY coatings and the CMSX-4 substrate. Isothermal oxidation testing results are presented in Part II of the study, which reveals the oxidation performance of the NiCoCrAlTaY coatings produced using the proposed CS process.