Evaluation of hot corrosion behaviour of HVOF sprayed Ni-5Al and NiCrAl coatings in coal fired boiler environment

Hot corrosion was recognised as a serious problem in connection with the degradation of fireside boiler tubes in coal fired steam generating plants. It is one of the most deleterious forms of surface degradation which can lead to the loss of mechanical strength and catastrophic failure of structural and engineering components. In the present investigation, an attempt has been made to evaluate the hot corrosion behaviour of high velocity oxyfuel (HVOF) sprayed Ni-5Al and NiCrAl coatings on iron based superalloy in an actual coal fired boiler environment. The coated specimens were hung in the low temperature superheater zone (similar to 700 degrees C) of a coal fired boiler. The studies were carried out for 10 cycles each cycle consisting of exposing the coated specimens for 100 h followed by 1 h cooling to ambient conditions. NiCrAl coated specimen provided better resistance to hot corrosion than Ni-5Al coated specimen in the given environment.