Hot Corrosion Behavior of a Novel Co-base Superalloy in Molten NaCl at 900℃

Abstract

Hot corrosion behavior of a new cobalt-base superalloy at 900℃ in the molten NaCl was investigated by salt-leaching method. The results show that the selective oxidation occurs at the initial stage of corrosion, and the oxidation films including Al2O3, Cr2O3 and a small amount of TiO2 are formed on the surface of the superalloy. However, the protective Cr2O3 and Al2O3 are corroded by the molten NaCl and then the substrate is exposed to the corrosive substances, so that the corrosion rate is accelerated. During the corrosion, rod Al2O3 is formed in inner corrosion layer, and then Co3W is easily formed around Al2O3 owing to the depletion of Al element in the matrix. As a result, a fast path for O diffusion is formed in the interface between Co3W and rod Al2O3 phase, resulting in the increase of hot corrosion rate after 80h.

Keywords

• Co-base superalloy
• molten NaCl
• hot corrosion