Optimizing NiCr Thermal Spray Coating with Process Map Methodology for High Temperature Power Plant Boiler Application

Alloys with high amount of chromium are used for protection of power plant boilers especially against the high temperature corrosion, especially heat exchanger surfaces, such as superheaters. Thermal spray coatings can be applied to low alloyed steel in order to enhance the lifetime of the cheap substrate material. In this study NiCr (50Ni49Cr1Fe) powder was sprayed with DJ Hybrid and CJS HVOF techniques, and the spraying process was optimized with process map methodology, including SprayWatch for measuring the temperature and velocity of the spray stream, and ICP (In-situ coating property measurement) for measuring the stress state and CTE (coefficient of thermal expansion). Different spraying parameters were applied in order to attain the best suitable coating characteristics for high temperature applications, such as high density and low oxidation stage. The coatings were analyzed e.g. by microscopic means and mechanical testing. The use of process map methodology and following coating characteristics are presented.