Abstract
Hot corrosion behaviors of CoCrFeNiTi0.5 high entropy alloy pre-coated various mixture salt in air at 750°C were investigated respectively by using weight change kinetics, X-ray analyses, SEM equipped with EDS and EPMA. The results indicate that CoCrFeNiT0.5 alloy exhibits relatively high corrosion resistance in Na2SO4-25%K2SO4 molten salts. The cross-section is divided into three parts: the oxide scale composed of various oxides, the corrosion affected zones with some micro-pores as well as minor of sulfides and the matrix. The addition of NaCl to Na2SO4 destroys seriously the integrity and compactness of the oxide scale and induces the formation of more micro-pores as well as sulfides in the corrosion affected zone, which accelerates the propagation of hot corrosion. As a result, the alloy suffers from more severe corrosion in Na2SO4-25% NaCl than in Na2SO4-25%K2SO4. Hot corrosion of the alloy in Na2SO4-25%K2SO4 is explained based on the oxidation and the basic fluxing of Cr2O3 in molten Na2SO4. However, hot corrosion process in Na2SO4-25% NaCl is dominated by the interaction of oxidation and chlorination. In addition, the internal sulfidation of Fe and Ni also contributes to hot corrosion of the alloy in both Na2SO4-25%K2SO4 and Na2SO4-25% NaCl mixture salt.
Highlights
Compared with the conventional practical alloys, high entropy alloys (HEAs) exhibit a series of excellent performance, such as the superior resistance to corrosion, oxidation, wear and high temperature [1,2,3,4,5] as a result of their simple solid solution structures and ease of amophization or nanoprecipitation [6,7,8]
The aim of the present study is to investigate hot corrosion resistance and highlight the mechanisms of CoCrFeNiTi0.5 alloy pre-coated Na2SO4-25% K2SO4 and Na2SO4-25% NaCl in air at 750°C
The alloy suffers from slight severe attack in the environment of Na2SO4-25%NaCl mixture, the corrosion rate of CoCrFeNiTi0.5 alloy seems to higher and follows a nearly linear law, indicating the addition of NaCl accelarates the corrosion of the alloy
Summary
Compared with the conventional practical alloys, high entropy alloys (HEAs) exhibit a series of excellent performance, such as the superior resistance to corrosion, oxidation, wear and high temperature [1,2,3,4,5] as a result of their simple solid solution structures and ease of amophization or nanoprecipitation [6,7,8]. Hot corrosion of metals or alloys is a type of accelerated damage caused by the deposition of a thin film of molten salts on the material surfaces in the temperature interval between 650°C and 1000°C [12,13,14]. The existence of such corrosive condensation layer on the surface can considerably reduce the service life of high temperature components [15]. A few data on hot corrosion behaviors of HEAs in aggressive environment, such as high temperature, corrosive servicing gases and deposition of
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