Hot corrosion behavior of Mo-9.0Si-8.0B

In recent years, interest in Mo-based alloys has increased significantly due to their promising high-temperature behavior and their possible uses for industrial high-temperature applications such as within turbines. An important corrosion mechanism in turbines is the sulfate salt-induced attack of the structural materials, known as hot corrosion. Therefore, the Type I and II hot corrosion behavior of Mo-9.0Si-8.0B was investigated at 700 degrees C and 900 degrees C for 24 and 100 h. The Mo-based alloy showed severe degradation, but not by sulfates. Thus, the underlying hot corrosion mechanism through molybdate fluxing, which is accompanied by Mo oxide evaporation, is discussed in detail. At the higher temperature, the MoO3 evaporation becomes predominant, leaving behind a Si-glass with molybdate inclusions. The hot corrosion mechanism of the Mo-9.0Si-8.0B alloy at 700 degrees C and 900 degrees C is superimposed by its pesting behavior, leading to the formation of an unprotective SiO2 scale and Mo oxides (MoO2 and MoO3). The low melting Na2MoO4-MoO3 eutectic leads to the formation of a liquid phase and replaces the role of SO 42 - ${\text{SO}\,}_{4}<^>{2-}$ as the acidic component. image