Mechanical alloying of cold-sprayed Ni-Nb-Si composite coating by friction stir processing: Improvement in microstructure and resistance against molten silicates corrosion

In this study, for the first time the Ni-Nb-Si composite coating system was prepared on the In718 superalloy substrate by solid-state cold spraying and modified by solid-state friction stir processing (FSP) to improve the high-temperature corrosion resistance of the coating in molten glass. The microstructure and corrosion behavior of the as-sprayed and FSPed coatings were characterized. Results show that a dense Ni-Nb-Si composite coating has been obtained, but the corrosion resistance of the as-sprayed coating is poor because of the unbonded interfaces between individual particles. Strong thermomechanical coupling during FSP not only promotes the refinement of coating microstructure with most original interfaces eliminated in the stirred zone under, but also facilitates the formation of intermetallic compounds such as NbNi₃ and Nb_0.1Ni_0.9. The densification and alloying greatly improves the corrosion performance of the coating in molten glass corrosion at 1050 °C.