Rupture of alumina coatings on C35 steel: A numerical simulation

The knowledge of the rupture mechanism of multilayer systems is necessary for improving the bonding of materials, particularly for the ceramic-to-metal junctions, and especially in the case of the ceramic coatings on metallic substrates. For this purpose, coupling experimental measurements of macroscopic interfacial adhesions with numerical tools of fracture mechanics allow understanding how the stress distribution and the cracking mechanisms are influenced by the local environment. This brings an explanation to the cracks initiation and propagation and to the role of local characteristics of the interfacial zone. The present work illustrates this, in the case of alumina coatings strongly bonded to C35 steel substrates previously pre-oxidized in CO2. The experimental tool is based on the "silver print test". It consists in covering the central part of the samples with a thin layer of silver paint before coating in order to create a defect zone. Concerning the numerical part, the finite element method is used as a powerful tool to describe the mechanical phenomena at the local scale influencing the crack propagation. The obtained numerical results show a good agreement with the experimental observations and they allow a local description of the phenomena influencing the cracking mechanism. Moreover, they lead to a concrete proposition for improving the coatings adherence.