Effect of Dy_2O_3 on the Hot Corrosion of Ni-Based Superalloy K3 beneath Na_2SO_4-V_2O_5 Film at 1073K in Air by Electrochemical Impedance Spectroscopy

摘要

This paper reports comparative investigations of the effects of Dy_2O_3 and MgO additives on the hot corrosion of nickel-based alloy K3 beneath Na_2SO_4-V_2O_5 film at 1073K in air by using electrochemical impedance spectroscopy. It was shown that the Dy_2O_3 additive could react with V_2O_5 to form a refractory compound DyVO_4, and reduced dramatically the corrosion of the alloy due to the formation of a porous, friable deposit and of a protective Cr_2O_3-rich layer. Correspondingly, the electrochemical impedance spectra were composed of two capacitive loops. In contrast, the electrochemical impedance spectra for the corrosion in both Na_2SO_4-V_2O_5 and Na_2SO_4-MgO environments exhibited the typical features of a diffusion-controlled reaction. The MgO additive could decrease the corrosiveness of Na_2SO_4-V_2O_5 by the formation of magnesium vanadates and promoting the formation of a protective Cr-enriched scale, but with less effectiveness than the Dy_2O_3 additive.