High Velocity Air Fuel Sprayed Ni- and Fe- based Coatings for Enhanced Corrosion Resistance

Cavitation and corrosion are major challenges for components like hydro power turbines, steam turbine blades, pumps, and valves. Ni-based and Fe-based alloys are potential coating materials to mitigate these issues. High Velocity Air Fuel (HVAF) spraying, with its high kinetic energy and limited thermal energy, minimizes in-flight damage such as oxidation and decarburization. Fe-based alloys, depending on their phases (hard martensite or soft austenite), effect cavitation and corrosion performance. On the other hand, Ni-based superalloys are hard to deposit due to the high strength of the material. In this regard, the state of the feedstock powder at moment of impact with the substrate plays a crucial role in dictating the deposition characteristics and the coatings performance as well. This study investigates the effect of powder heat treatment on the deposition and corrosion behavior of Ni-based (IN718) and Fe-based (18Ni300Fe and 17-4PH) alloys sprayed using HVAF. The coatings were characterized using XRD, SEM, and EDS, and their mechanical properties (elastic modulus and hardness) were tested. Elastic modulus was used to assess inter-splat bonding, while corrosion performance was evaluated through electrochemical testing in a 3.5% NaCl solution. Post-corrosion analysis was performed using SEM, EDS, XRD, and XPS to better understand degradation mechanisms.