Preparation and laser protection mechanism of polysilazane-derived Si–C–N–O/ZrO₂ composite coatings under large-area laser irradiation

Continuous-wave laser irradiation poses severe thermal threats to metallic structures in extreme service environments. However, most reported protective coatings have been evaluated under small-spot irradiation conditions (<1 cm²), leaving large-area protection strategies underexplored. In this work, polysilazane (PSZ)/ZrO₂ composite coatings with varying ZrO₂ loadings were fabricated on 2A12 aluminum alloy via a brush-coating process and evaluated under large-area (>5 cm²) continuous-wave laser irradiation (1064 nm, 500–1500 W/cm²). The effects of ZrO₂ loading on coating morphology, optical reflectivity, thermal response, and failure behavior were systematically investigated. The PSZ matrix underwent pyrolysis at 500–750°C, followed by polymer-to-ceramic transformation via Si–H and Si–N bond cleavage, ultimately forming a dense Si–C–N–O/SiO₂ ceramic layer above 750°C. The coating with a PSZ:ZrO₂ mass ratio of 1:1 achieved the optimal balance, exhibiting a reflectivity of 96% at 1064 nm and maintaining the substrate backside temperature at approximately 80°C under 1500 W/cm² irradiation. In contrast, excessive filler loading (PSZ:ZrO₂ = 1:1.5) disrupted ceramic matrix continuity, resulting in through-thickness cracking and coating failure under high-power irradiation. A synergistic protection mechanism coupling laser reflection, endothermic polymer pyrolysis, and ceramic thermal shielding was proposed. This work provides an effective strategy for designing high-performance ceramic coatings for large-area laser protection applications.