EROSION-CORROSION STUDIES OF HVOF SPRAYED Cr3C2-NiCr COATED BOILER STEEL AND .Fe-RASED SUPERALLOYS

Abstract

The boiler tubes of energy generation system are subjected to erosion corrosion mode of degradation in the platen superheater zone of the boiler which results to the shutdown of the plant and more than 50% of total production cost is used in replacing these eroded corroded parts of the boiler. No alloy is immune to erosion corrosion mode of degradation .Even the superalloys degrade due to this mode of attack if they are used continuously for longer period of time. Therefore the boiler tubes used to be protected by applying the coatings which provide the requisite resistance to erosion corrosion whereas the alloy provides the necessary mechanical strength. There are several coatings and various coating processes that are available these days to combat this problem. But these are highly condition and environment specific. Thus these parameters are to be experimentally evaluated so that their effects are clearly understood. One such coating, Cr3C2-NiCr is known for its resistance against oxidation at high temperatures (nearly 7500 C). thus in this work Cr3C2-NiCr coating on Fe based superalloy(Superfer 800) samples (size 25X20X5) have been used for erosion test on "Air jet impact erosion tester"(TR 470). The tester provides with the option of erosion being carried out at different orientations to identify the relative degree of erosion. This helps in understanding the mechanism of erosion. Alumina oxide has been used as erodent which was fed into the tester after proper treatment. The samples have been examined by SEM/EDAX to ascertain the mechanism of erosion and various phases coming out from it.