Laser-induced layer-by-layer removal and thermo-mechanical action mechanisms of FeCo-based multilayer wave-absorbing coatings

Abstract

The excellent performance of laser-induced removal has been widely recognized, yet the limitation of its applications has been gradually approached for complex multilayer coatings in practical situations. Therefore, it is necessary to clarify the laser-induced removal mechanisms of different material layers, which may contribute to guiding precise and controllable layer-by-layer removal and subsequent repair. Herein, the laser-induced layer-by-layer removal of FeCo-based multilayer wave-absorbing coatings was designed and verified. The macro/micro morphologies and elemental analysis indicated that the removal of the topcoat and wave-absorbing layer was dominated by thermal ablation. Interestingly, experiments and simulations demonstrated that a shift in the removal mechanism, i.e., from the ablation mechanism to the stripping mechanism, occurred when the laser irradiated the primer. It is mainly attributed to the competing contributions of temperature rise and thermal stress to the removal effect. Subsequent macrodynamic behavior captured by a high-speed camera also validated the combination of both removal mechanisms. Additionally, the evolution of the crystalline phase and element valence state was revealed. Further laser-induced breakdown spectroscopy revealed the microscopic material motions during the layer-by-layer removal, including molecular bond breaking induced by multiphoton absorption, atomic ionization, excitation and compounding of electrons and ions, crystal lattice deformation caused by electron-phonon coupling, etc. Based on the above analysis, the thermo-mechanical action mechanisms and microscopic motion models of laser-induced layer-by-layer removal for FeCo-based multilayer wave-absorbing coatings were established, which is expected to be an ideal method for breaking through the limitation of laser-induced removal's applications.