The effect of powder particle size on microstructure, mechanical and tribological properties of APS-IN718 coatings for repair applications

In order to understand the tribological properties of coatings used for thermal spray repair, two types of IN718 coatings with different particle sizes are prepared on the surface of IN718 alloy using Atmospheric plasma spraying (APS) technology. The microstructure, phase composition, mechanical properties, and tribological performance of APS-718 coatings across various temperatures are studied. The results indicate that the coating made from small particle size powder has a denser structure, smaller porosity, and higher oxide content compared to the coating made from large particle size powder, while also exhibiting higher surface Rockwell hardness, adhesive strength, and nanoindentation hardness. In the wear tests, both the coefficient of friction (COF) and the wear rate of the S-718 and L-718 coatings initially decreased and then increased, reaching their minimum values at 600 °C, with the COF and wear rate being 0.47, 0.52, and 0.67 × 10⁻⁵ mm³/N·m, 0.79 × 10⁻⁵ mm³/N·m, respectively. Under room temperature and low-temperature conditions, the wear mechanism is characterized by abrasive wear and oxidative wear; at intermediate temperatures, it transitions to adhesive wear and oxidative wear; while at high temperatures, due to severe softening of the glaze layer, the wear form changes to abrasive wear, adhesive wear, and oxidative wear. Furthermore, both coatings exhibit tribological properties similar to those of the IN718 alloy at intermediate to high temperatures, providing a reference for the repair of damaged areas in the hot sections of aerospace engines.