Some Observations regarding Erosion-Corrosion Performance of HVOFSprayed Cr_3C_2- NiCr and Cr_3C_2- NiCr-(25) WC-Co coatings in Actual Boiler Environment

摘要

Cr_3C_2-^sNiCr and Cr_3C_2-^sNiCr-(25) WC-Co coatings were deposited on T22 boiler steel by High Velocity Oxy-Fuel (HVOF) Technology. The coated as well as the uncoated steel samples were exposed to the actual boiler environments in a thermal power plant for 1500 hrs under cyclic conditions to evaluate their erosion-corrosion performance. Weight change measurements were taken for each sample after every 100 hrs. It has been observed that the weight change trends for coated steel with Cr_3C_2-^sNiCr and Cr_3C_2-^sNiCr-(25) WC-Co coatings followed a parabolic trend. The exposed samples were physically investigated for any macroscopic changes after each cycle of 100 hours. The uncoated steel showed blisters and spallation of its oxide scale, whereas the coated samples exhibited intact oxide scales, in general. Scanning Electron Microscopy/Energy Dispersive X-Ray Analysis (SEM/EDAX) was done to characterize morphology of the oxide scales. The protective nature of coatings has been explained based on the results of the study.