The evolution of crevice corrosion damage on the Ni–Cr–Mo–W alloy-22 determined by confocal laser scanning microscopy

Crevice corrosion of alloy-22 was studied galvanostatically (10–200 μA) at 120 °C in 5 M NaCl. Corrosion damage was analyzed by confocal laser scanning microscopy to obtain penetration profiles. Three-dimensional images demonstrate that damage morphologies varied with applied current. At low applied currents (⩽70 μA), propagation predominantly leads to penetration into the alloy, whereas at higher applied currents (>70 μA) corrosion damage spreads across the alloy. Limited penetration depths at higher currents are attributed to metal dissolution inhibition by the rapid formation of insoluble molybdates, which force propagation to shift to areas unprotected by molybdate layers.

► Crevice corrosion of alloy-22 was studied galvanostatically at 120 °C in 5 M NaCl. ► Corrosion damage was analyzed by confocal laser scanning microscopy. ► At low applied currents (⩽70 μA), propagation mainly penetrates into the alloy. ► At higher applied currents (>70 μA) propagation spreads across the alloy surface. ► Insoluble molybdates forces propagation to shift to areas unprotected by molybdates.