To enhance the anti-laser ablation performance of AlN/Al coatings, T₁ gradient coating with gradient distributed AlN content was fabricated. Simultaneously, to further validate the anti-laser ablation performance of the gradient coating, L coatings with uniform AlN contents but varying thicknesses were also prepared. The microstructural characteristics and anti-laser ablation performance of these coatings were systematically investigated. The study found that all coatings exhibited favorable surface quality, dense microstructures and nanoscale AlN distributed in network morphologies. The T₁ gradient coating exhibited a low AlN content in the top region and a high content in the bottom region. Apart from the difference in AlN content between the top and bottom regions of the T₁ gradient, the morphology, size and distribution of AlN resembled those in the L coatings. Under identical laser ablation conditions, the ablation zone diameter in the L coatings decreased to 4.3 mm as thickness increased. Whereas the T₁ gradient coating achieved a much smaller ablation zone diameter of only 1.9 mm, indicating significantly mitigated damage severity. The L₂₀ coating readily developed voids and underwent substrate thermal softening from continuous interfacial heat accumulation. In contrast, the T₁ gradient coating employed a graded AlN distribution with low AlN content in the top region and high AlN content in the bottom region. Such a gradient structure relieved the thermal expansion mismatch and reduced internal stress. The dispersed micro voids blocked the heat conduction paths, while the high-AlN bottom region provided effective structural reinforcement. These synergistic mechanisms suppressed crack propagation and void enlargement, preserved integrity and conferred superior anti-laser ablation performance.
 

AlN/Al coatings; layer thickness; gradient structural design; laser protection; anti-laser ablation performance