The adhesion of growing oxide scales to the substrate

Overview & Synopsis

There is only limited new understanding of the structure of the evolving dynamic metal/oxide interface itself but there is valuable circumstantial evidence from cooled specimens and from other interfaces. Identification of flaws for crack initiation, definition of a composite defect and elaboration of delamination models, involving a plastically-relaxed crack tip region, have been undertaken. Loss of adhesion has received more attention, by the alternatives of film buckling or crack propagation along the metal/oxide interface by wedging, including cases where stress relief occurs by creep. Mapping of scale failure modes has progressed. Computation and modelling using electronic and atomistic models are useful, but "clean" metal/oxide and contaminated interfaces require in-depth work. Stress development and relaxation are complex. Models involve dislocation climb and the role of vacancy transport and cavity development. Sweeping of various particles by moving boundaries is receiving renewed analysis. The role of convoluted metal/oxide interfaces in promoting or diminishing adhesion has been analysed quantitatively. Explanation of reactive element effects by the embedded atom method is instructive, as are the relative roles of S and P in weakening interfacial adhesion.