Effect of surface roughness on corrosion behavior of the superalloy IN718 in simulated marine environment

This work presents the effect of surface roughness on corrosion behavior of the superalloy IN718 in simulated marine environment of gas turbine engine, at 600 °C. Samples of varying roughness (400-1000 grit) were spray coated with salt 1S (100 wt% NaCl) and salt mixtures 2SM (60 wt% Na2SO4+ 40 wt% V2O5) and 3SM (75 wt% Na2SO4+ 15 wt% NaCl+ 10 wt% V2O5) and exposed at 600 °C in air up to 100 h. The corrosion products were characterized by using XRD, SEM/EDS and EPMA. Corrosion kinetics showed that the rate of corrosion was highest for the lS coated sample at all levels of the surface finish followed by that coated with 3SM and was lowest for the 2SM coated sample. The plots of corrosion kinetics clearly indicate that the oxide layer was less protective at higher surface roughness due to larger surface area and enhanced diffusion of corrodants in the material.