Studies on Erosion and Oxidation Behaviour of Cobalt-Based Coatings

Abstract

AbstractThis work aims to investigate the performance of different cobalt-based coatings such as Stellite 6 (St6), WC-Co (W1) and Stellite 21 (St21) on the different grades of boiler steel. The different grades of boiler steel chosen for this purpose are SAE213-T91(BS1), SAE213-T12 (BS2) and SAE 208 (BS3). Coating powders were deposited on the selected substrate materials under different impact angles (30º and 90º) using the detonation gun spray method. The properties of the coatings were assessed using an optical microscope, microhardness tester and surface roughness tester. In addition, an erosion and oxidation study of the coating was also carried out for quality check of the coatings. The erosion test was performed at room temperature as well as an elevated temperature of 400 ºC. The cyclic oxidation of different coated samples was carried out in air at 900 ºC for 50 cycles of 1 h duration. The result shows that at room temperature, the erosion resistance of W1 coated boiler steel substrate is higher than that of steel substrate coated with St6 and St21 powder. But, at an elevated temperature of 400 ºC, their resistance to erosion resistance decreases significantly which may be due to the phase softening. St6 and St21 coatings are found to be successful in lowering the oxidation rate of SAE 213-T91 boiler steel. This may happen due to the formation of a protective Cr2O3 phase along with CoCr2O4 phase in the oxide scale.KeywordsErosion wearOxidationCobalt-based coatingBoiler steels