Novel Surface Modification Method for Ultrasupercritical Coal-Fired Boilers

To increase efficiencies, ultrasupercritical (USC) coal-fired boilers are being developed to operate with steam temperatures up to 760oC and steam pressures up to 37.9MPa. However, the increasing temperatures and corrosive environment cause more severe oxidation and corrosion in USC boiler components. New surface modification technology is needed to solve the corrosion problem. Therefore, this project will develop an innovative process for forming an ultrafine-grain alloy coating at a competitive cost, and will evaluate and optimize coating materials and structures for high-temperature oxidation and corrosion resistance. The ultrafine structured alloy coating will provide a high adherence strength, due to the high-degree melting of fine-sized particles, and improved corrosion resistance, which would result from the reduced deposit and penetration of corrosive ash and salts. Phase I will involve the development of an innovative coating technique; the optimization of coating materials and structures; and the evaluation of the ultrafine-grained alloy coatings with respect to microstructure uniformity, corrosion resistance, mechanical properties, and surface quality. Corrosion resistance of the alloy will be determined from isothermal and cyclic oxidation tests and from hot corrosion in molting salts. In Phase II, the process will be scaled up and coating tested in simulated boiler components. Commercial Applications and Other Benefits as described by the awardee: Potential applications should include supercritical and ultrasupercritical boiler components, coal gasification systems, hot-section components of land-based gas turbine engines and aerocraft engines, and other industry components involved in oxidation and corrosion at elevated temperatures. The process technology is expected to be competitive in cost, have both in-house and on-site applicability, provide a high deposition rate and efficiency, and minimize the overyspray-induced environment concern