Universal characteristics of an interfacial spalling cyclic oxidation model Original Research Article

A mathematical model has been generated to represent the iterative, discrete growth and spallation processes associated with cyclic oxidation. Parabolic growth kinetics (kp) and a constant spall area (FA) were assumed, with spalling occurring interfacially at the thickest region of the scale. Although most models require numerical techniques, the regularity and simplicity of this progression permitted an approximation by algebraic expressions. Normalized responses reflected all parametric effects and yielded a universal cyclic oxidation expression:Wu=12{3Ju1/2+Ju3/2},where Wu is weight change normalized by the maximum and Ju is the cycle number normalized by the number to reach maximum. Similarly, the total amount of metal consumed was represented by a single normalized curve, using the figure of merit [(Sc−1)·(FAkpΔt)1/2], where Sc is the scale mass ratio of oxide to oxygen and Δt is the cycle duration. Also, a universal or invariant cyclic oxidation failure map was constructed in normalized kp–FA space.