Comparative study of Y₂O₃, SnO₂ and ZrO₂ as inhibitor to control high temperature corrosion of Ni-based superalloy

High temperature corrosion of metals and alloys can be controlled by the use of inhibitors and fuel additives. In this work three different types of coatings namely Y2O3, SnO2 and ZrO2 coatings were superficially applied on Ni base superalloy Superni 718. Accelerated corrosion testing of the uncoated as well as the coated superalloy was done in a molten salt environment (Na2SO4-60%V2O5) at 900 degrees C for 50 cycles. Each cycle consisted of 1 hour heating in a Silicon Carbide Tube furnace followed by 20 minutes cooling in ambient air. Weight change measurements after each cycle were taken by an electronic balance having an accuracy of 0.01 mg. XRD, SEM and EPMA analyses of the exposed specimens were carried out to characterise the oxide scales. The bare superalloy showed more overall weight gain, in comparison with all the coated counterparts. It was concluded that ZrO2 was most effective in reducing corrosion rate in alloy A.