High temperature corrosion behaviour of some Fe-, Co- and Ni-base superalloys in the presence of Y2O3 as inhibitor

High temperature corrosion is accelerated degradation of materials at higher temperatures of operation caused by the presence of a deposit of salt or ash. Inhibitors and fuel additives have been investigated with varying success to control this type of corrosion. In this work, effect of an oxide additive namely Y2O3 on the hot corrosion behaviour of some superalloys viz Superfer 800H (alloy A), Superco 605 (alloy B) and Superni 75 (alloy C) has been investigated in an Na2SO4-60%V2O5 environment at 900 °C for 50 cycles. Each cycle consisted of 1 h heating in a Silicon Carbide Tube Furnace followed by 20 min cooling in ambient air. Weight data were taken by an electronic balance having an accuracy of 0.01 mg after each cycle. Subsequently, the exposed alloys were characterized by XRD, SEM and EPMA analyses to evaluate the role of the oxide additive. In the Na2SO4-60%V2O5 environment, the corrosion rate for the Co-base alloy was found to be highest, whereas that for the Ni-base Superni 75 the lowest. Superficially applied Y2O3 was observed to be useful in reducing the high temperature corrosion of the alloys. It was found to be most effective for the alloy A for which the oxide scale was continuous and rich in protective Cr. Alloy B showed the formation of medium size scale rich in Cr and Co. The oxide scale for the alloy C contained mainly Cr and Ni.