Abstract:Multi-elements alloy with good thermal stability is expected to serve as the superheater tube material of ultra-supercritical boiler and may suffer from hot corrosion under the coal-fired atmosphere. In this study, the corrosion resistance behavior of multi-elements alloy CoCrFeNiTi0.5 coated with alkali metal sulfate at 750 °C was investigated. The results show the corrosion kinetics curves of the alloy follow parabolic growth rate and the corrosion products, which consist of volatile Na4(CrO4)(SO4), (Fe, Ni) sulfide, Cr/Ti oxide as well as compound oxides with spinel structure, form on the surface and sub-surface of the alloy. The oxide layer is dense and has good adhesion with the matrix at the beginning of corrosion. With the corrosion time increasing, the oxide layer in thickness increases and becomes loose as well as porous. The micro-pores are generated in the interface between the oxide scale and matrix with the formation of the internal oxidation and internal sulfidation. In a word，the corrosion resistance behavior of multi-elements alloy CoCrFeNiTi0.5 at 750 °C can be attributed to the formation of the protective oxide layers and to the basic fluxing in molten Na2SO4 induced by low melting point eutectic.