Performance of cold sprayed Ni based coatings in actual boiler environment

Abstract

Hot-corrosion combined with erosion-corrosion is a severe problem in boiler tubes of Power Plant Boilers. One possible way to control hot corrosion is the use of thermal spray protective coatings. Cold gas dynamic spraying (CGDS), popularly referred to as cold spray (CS), is a promising technology for depositing protective coatings. Ni based alloys have been used for thermal spraying for various applications. In the current research work three different types of coatings NiCr, NiCrTiC and NiCrTiCRe were deposited by the cold spray technique on SA 516 steel. The performance of the coatings was evaluated in actual boiler conditions wherein the uncoated and coated steels were exposed to the superheater zone of a coal fired boiler for 15cycles. The change in weight and thickness were noted and used for studying the kinetics of the erosion-corrosion. X-ray diffraction, surface and cross-sectional FE-SEM/EDS and X-ray mapping techniques were used to evaluate the as-coated and eroded-corroded specimens. It was observed that the coated specimens gave better performance than the uncoated steel. The development of oxides and spinels of nickel and chromium might have resulted in better performance of the coatings. The NiCrTiCRe coating established best erosion-corrosion resistance behavior amongst all the investigated specimens.