Rational design of laser-induced precise removal for FeCo-based wave-absorbing coatings aiming at non-destructive substrates

Laser-induced removal of non-destructive substrates is a continuous pursuit for practical applications. Herein, a strategy of scanning cycle's large adjustment combined with laser energy density's fine tuning was established to achieve precise removal of FeCo-based wave-absorbing coatings. First and foremost, no coating residue was observed on the surface and cross-section of optimized sample E5 with a laser energy density of 61.1 J/cm2 (scanning cycles were seven). CIE LAB color analysis indicated that the surface of sample E5 had the highest coating's removal degree. Through numerical simulation and experimental examination, the oxide layer of the aluminum alloy did not present any damage such as cracking and peeling. In addition, the surface roughness remained unchanged, which verifies the possibility of laser removal towards non-destructive substrates. The multi-perspective evaluations of surface states illustrated that Barite (BaSO4), FeCo and other coating's characteristic substances had disappeared, ensuring the subsequent serviceability of the surface after removal. Furthermore, the vaporization removal mechanism of the wave-absorbing coatings was demonstrated by the plasma captured by a high-speed camera. Notably, the substrate's damage mechanism in laser removal was revealed. The remarkable different thermal expansion behavior of oxide layer and alloy induced extreme stress concentrations at the interface, which led to oxide layer's cracks and exfoliation. In summary, substrate's damage suppression can be achieved through simulation and experimental optimization. The presented research not only benefits the strategy design of laser removal for multilayer materials, but also expands the application potential of laser removal in non-destructive substrates.