Jusqu’à quel point optimiser la microstructure des revetements de surface ?

To which extent is the microstructure of surface coatings to be optimized ?

¹ Laboratoire de Métallurgie Physique, URA CNRS 234, Université de Lille I, Villeneuve d’Ascq
² ENSAM, CER Lille

Abstract

In the galvanizing process, the great difference between the linear thermal expansion of iron substrate and the intermetallic compounds of the coating has been found to be the source of an important deformation gradient which promote crack formation in the δ-phase. The critical stress intensity factor Kc, can be considered as one of the most important parameters for the prediction of the toughness of brittle materials. Using Kc=2MPa√m, value determined by microhardness measurements, a crack network size dc of about 5 μm been obtained, which agrees with experimental observations. Considering the energy consumption, a modelling based on the relaxation of the thermal and external strains by cracks is proposed. This result emphasizes the role of the most brittle intermetallic compound. The concept of constant energy release rate for mode I and mode II propagation in δ led to establish relationship between the cracks network and the morphological feature of the layer.