A mechanics-based approach to cyclic oxidation

The failure process of cyclic oxidation,which Involves both the formation and spallation of oxides, has been treated using a mechanics approach, in which oxidation is described via :a parabolic growth law, while spallation is treated in terms of a power law derived from a fracture mechanics analysis. The spallation model is formulated on the basis that shear cracks are induced by thermal stresses during the cooldown period of a thermal cycle. Some of the shear cracks: develop wing tip cleavage cracks, whose propagation and linkage with other shear cracks lead to the formation: of oxide fragments that separate from the oxidizing surface during cooldown: Using a mass balance, quantitative relations are obtained-between the process driving force, which is the thermal stress, and the response parameters such as the weight of oxide spalled, weight gain, and weight loss of the oxide-forming element. Applications of the proposed model for,predicting the cyclic oxidation behavior of metal substrates and coating materials are demonstrated by comparing:model calculations against experimental data as well as against other models in the literature.