Early Material Damage in Equimolar CrMnFeCoNi in Mixed Oxidizing/Sulfiding Hot Gas Atmosphere

The challenges to use more varied fuels at medium and high temperatures above 500 °C need to be addressed by tuning the materials toward a better resistance against increased corrosion. As a first step the corrosion processes need to be better understood, especially in the case of the unavoidable and highly corrosive sulfur‐based gases. Herein, oxidation/sulfidation of an equimolar CrMnFeCoNi high‐entropy alloy is studied at an early stage after hot gas exposure at 600 °C for 6 h in 0.5% SO 2 and 99.5% Ar. The oxidation process is studied by means of X‐ray diffraction, scanning and transmission electron microscopy, and supported by thermodynamic calculations. It is found that the sulfur does not enter the bulk material but interacts mainly with the fast‐diffusing manganese at grain boundary triple junctions at the alloy surface. Submicrometer scaled Cr–S–O‐rich phases close to the grain boundaries complete the sulfur‐based phase formation. The grains are covered in different Fe‐, Mn‐, and Cr‐based spinels and other oxides.