HIGH TEMPERATURE OXIDATION BEHAVIOUR OF Cr_3C_2-NiCr COATINGS DEPOSITED BY HIGH VELOCITY OXY-FUEL (HVOF) TECHNOLOGY

摘要

Cr_3C_2-NiCr coating was deposited on T22 boiler steel by High-Velocity Oxy-Fuel (HVOF) Technology. The coated as well as the uncoated steel samples were subjected to cyclic oxidation for 50 cycles in air at 700°C to evaluate their high temperature oxidation performance. Each cycle consisted of one hour heating in a silicon carbide tube furnace followed by 20 minutes of cooling in ambient air. Weight change measurements were taken for each sample after every cycle to establish the kinetics of corrosion. It has been observed from the weight change trends that the Cr_3C_2-NiCr coating was found to be successful in reducing the overall weight gain by T22 steel when exposed to the cyclic oxidation. The uncoated steel showed blisters and spallation of its oxide scale, whereas the coated sample exhibited intact oxide scale. The overall weight gain by T22 steel was found to be 106.99 mg/cm~2, which was much higher than that conceived by the coated steel. Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS) analysis of the oxidised coating showed the possible presence of oxidation protective phases such as Cr_2O_3 and SiO_2 in its oxide scale. The microstructure of the scale for the coated steel was found to be uniform consisting of nodules which were rich in Cr and O, whereas the scale for the uncoated steel mainly consisted of Fe and O.