High Temperature Corrosion Behavior of Some Ni-Base Superalloys in the Presence of ZnSO_4 as an Inhibitor

摘要

High temperature corrosion is an accelerated form of corrosion occurring at higher temperatures in the presence of an oxidizing gas and is associated with a thin electrolytic deposit (salt or ash) on the alloy. Superalloys are used to resist this type corrosion and success has been achieved to a considerable extent, however they still lack resistance to such type of corrosion during longer durations of usage. Inhibitors and fuel additives have also been used with varying success to combat the same. In the present investigation, hot corrosion studies were conducted on two Ni-base superalloys namely Superni 718 and Superni 601 in a simulated environment of boilers (Na_2SO_4-60%V_2O_5) with and without the presence of ZnSO_4 as an inhibitor. The hot corrosion tests were carried out under cyclic conditions at 900℃, and the corrosion products were characterized by SEM, XRD and EPMA analyses. The ZnSO_4 addition resulted in reduction in corrosion rate for both the alloys, and effectiveness of the inhibitor was nearly similar for both the alloys. In the presence of the inhibitor, a protective Cr_2O_3 layer was seen just above the substrate in Superni 718, whereas for the alloy Superni 601, there was richness of Cr just above the substrate/scale interface and refractory vanadates especially Ni(VO_3)2 were seen in the scale.