Applying Ni-WC as a Composite Coating Combines both Protective and Repair Functions by Thermal Spray for HPTB Applications

This work presents a solution to repair the deteriorating High-Pressure Turbine Blades (HPTB) instead of costly replacement by implementing a two-coating layer system for protection and repair. The first layer is a Bonding Coating (BC) that is made from a nickel-based alloy (NiCrBSi); the second layer is a Top Coating (TC), which is composed of a nickel-based composite material that contains tungsten carbide (WC) particles. Both layers were applied to a nickel-based substrate using a flame thermal spraying (FTHS) technique, with the spray parameters chosen based on the Taguchi method. The results were analyzed using optical microscopy, scanning electron microscopy (SEM), and energy-dispersive X-ray spectroscopy (EDS). The findings indicated that a coating layer with a thickness of 200–300 μm was successfully deposited using the FTHS method. The optimal spraying parameters determined by the Taguchi method were: a spraying distance (SOD) of 150 mm, a feed rate (FR) of 30 g/min, and a transverse velocity (TV) of 300 mm/min. Among these factors, SOD was identified as having the greatest influence on the spraying process, followed by FR, and then TV. A crack area on HPTB was successfully repaired using an improved FTHS process, resulting in a homogeneous, dense, and crack-free structure.