Fatigue behavior in the potentiostatic passive corrosion regime of the iron-base superalloy A-286

Surface crack initiation and propagation behavior of the iron-base superalloy A-286 were tested using smooth hourglass specimens under passive corrosion conditions. In the very underaged (VUA) condition, cracks were initiated at slip steps (stage I) and later propagated in a stage II mode, resulting in a minimum or dip in crack growth rate. For the highly overaged condition (HOA), cracks initiated at inclusions, and only stage II was observed; therefore, anomalies in crack growth behavior were not observed. A planar slip distribution, observed in VUA, was associated with a reduced crack growth rate. In general, the VUA microstructure was superior to HOA, as it exhibited an impressive combination of excellent mechanical properties, decreased susceptibility to corrosion, good resistance against crack initiation, and low crack growth rate, under corrosion fatigue conditions. Possible reasons for such behavior are discussed.