Effects of Electrolytic Y2O3 and YAG Coatings on Oxidation and Corrosion of IN617 Superalloy

Abstract

In this study, the effects of electrolytic Y2O3, Y2O3/Al2O3 double-layer, and composite [the latter two finally forming yittrium aluminum garnet (YAG)] coatings on the thermal cycle oxidation, hot corrosion in Na2SO4, and aqueous corrosion in 3.5% NaCl or 0.5 M HCl solution of IN617 superalloy were investigated. It was found that all coatings could significantly improve the resistance against thermal cycle oxidation at 1000 degrees C and hot corrosion at 900 degrees C. A porous and nonprotective Cr2O3 film was formed on the uncoated specimen, relatively revealing a high oxidation rate. Conversely, a uniform film containing MoO2 but less Cr2O3 was formed on the Y2O3-coated specimen, revealing the low oxidation rate. Furthermore, a more uniform film containing MoO2 and Al2O3 was formed on the YAG-coated specimen, revealing the least oxidation rate. All coated specimens were more corrosion resistant than the uncoated in 3.5% NaCl aqueous solution. The corrosion resistance in 0.5 M HCl aqueous solution was also much enhanced by the YAG coating. However, the Y2O3 coating could be thoroughly dissolved in HCl aqueous solution, resulting in a lack of protection. It was suggested that the YAG coating is the better choice for IN617 to be used in a variety of environments, including thermal cycle oxidation, hot corrosion in sulfates, and aqueous corrosion in saline or acid solution.