Effect of sulfur impurity on the nucleation of α-Cr precipitates in nickel-based alloys

Sulfur is considered an unfavorable element in metallic materials because of its potential to cause embrittlement, thereby prompting its removal. However, trace amounts of S impurities can influence the precipitation of the primary α-Cr strengthening phase in the heat-resistant 50Ni–30Cr–0.8Ti–6W–Fe alloy, and thus affect its creep strength. In this study, fine Ti₂S particles were observed in heat-treated 50Ni–30Cr–0.8Ti–6W–Fe alloys through high-sensitivity, high-resolution, and wide-field element analysis using aberration-corrected scanning transmission electron microscopy. The Ti₂S particles were distributed linearly with the adjacent α-Cr precipitates. The Ti₂S precipitates functioned as nucleation sites for α-Cr, thereby refining and increasing the hardness of the alloy. The findings of this work challenge conventional approaches to material design and emphasize the significance of design based on fundamental principles.