Modeling and characterization of optimized multicrystals by graduated microstructure coatings – MOCAMOR

The miniaturization of metallic components in industrial applications leads to a strong decrease of the ratio between the grain size and the part dimensions. This results in a considerable degradation of the mechanical properties of about 30%, persisting despite the optimization of the forming processes by increasing the temperature or the mechanical loading. The origin of the deterioration of the properties is linked to the delay in the activation of the deformation mechanisms for the truncated surface grains characterizing the multicrystalline state (by definition a multicrystal has few grains in its section compared to a polycrystal). This delay, caused by dislocations escaping through these free surfaces, creates a strong mechanical softening. The ambition of this project is to use a method of physical vapor deposition (PVD) of a material on a substrate of same chemical composition in order to restructure the subsurface area of the material by a gradual evolution of the microstructural characteristics of this type of deposit and thus to generate an adapted barrier to the dislocation escape. The fundamental and innovative challenge of MOCAMOR is therefore to understand the physical mechanisms of the plastic deformation taking place in the newly generated subsurface zone and in particular in the interfacial film/substrate zone, with the aim of recovering for multicrystalline materials mechanical performances similar to those of polycrystals, through the triptych optimization of the deposit - micromechanical characterization, fine microstructural analyses - numerical modelling.