DEVELOPMENT OF REPAIR METHODS FOR SINGLE CRYSTAL COMPONENTS USING THERMAL SPRAY PROCESSES

Repairing single-crystal turbine blades is critical due to their complex manufacturing and high material costs. Effective repair solutions are essential for extending the lifespan and performance of high-temperature components in gas turbines, leading to a growing interest in repair technologies. Therefore, this study investigates three thermal spray processes—Cold Gas Spraying, High-Velocity Air-Fuel Spraying, and Vacuum Plasma Spraying — for their potential to repair single-crystal CMSX-4 substrates using CMSX-4 powder. Each process underwent parameter optimization, and the resulting coatings were evaluated for density and oxygen content, critical factors for repair applications. Single splat experiments were conducted to study microstructure formation. Additionally, residual stresses in the coatings were measured using the incremental hole-drilling method to provide insights into stress distribution of the coatings Adhesion properties were assessed through pull-off testing to evaluate the mechanical integrity of the coating-substrate bond. The optimized polycrystalline coatings were subjected to a controlled heat treatment in which the samples were intentionally passed through a high temperature zone. The aim of this process was to promote directional grain growth starting from the underlying single crystal substrate. After the heat treatment, the resulting grain structures of the coatings were analyzed by EBSD.