Modeling of corrosion fatigue crack initiation under passive electrochemical conditions

Abstract

A combined mechanical/electrochemical model has been developed which successfully predicts the corrosion fatigue initiation behavior of an iron-base superalloy using readily measurable electrochemical and mechanical properties. In particular, the model uses the current decay curve, the initial or bare metal corrosion rate, and the critical slip step height, a parameter associated with the transition from an intense slip band to an incipient crack. The exponential parameter,α, used to fit the early (short time) portion of the current decay curve has been found to scale with the fatigue crack initiation time, suggesting thatα could be used as a valuable screening aid to assess the corrosion fatigue susceptibility of any alloy under passive electrochemical conditions. The model permits accurate prediction of both the shape and magnitude of fatigue life (S-N) curves. The limitations and theoretical implications of the approach of this model are also discussed.