Surface micro-pits formation and anisotropic HAZ expansion of CF/PEEK under continuous laser spot irradiation

Significant differences in light absorption and thermal conductivity between carbon fiber (CF) and the polyetheretherketone (PEEK) matrix make surface damage and heat-affected zone (HAZ) control challenging during laser processing of carbon fiber reinforced PEEK (CF/PEEK). Continuous laser spot irradiation was performed under different levels of average power density (APD) and protective gas conditions. This work quantitatively distinguished the central crater boundary from the peripheral HAZ boundary and evaluated their different responses to APD, anisotropic heat conduction, and protective gas. The long and short axes and corresponding aspect ratios of the central crater and HAZ were measured. A Gaussian critical boundary model was used to assess boundary expansion, and an anisotropic transient heat conduction model was developed to interpret temperature field evolution. The results showed that laser irradiation produced a hierarchical morphology consisting of a central crater and an HAZ. The central crater was nearly circular, whereas the HAZ expanded elliptically along the fiber direction. The Gaussian critical boundary model described the central crater boundary to some extent but was not suitable for the HAZ boundary. Simulations indicated that increasing APD raised the peak surface temperature, while anisotropic heat conduction promoted heat diffusion along the fiber axis. Protective gas affected apparent morphology and boundary clarity, while simulations indicated that this effect could not be explained solely by enhanced convective cooling. These results reveal the formation mechanisms of the central crater and HAZ and provide a basis for independently controlling central surface damage and peripheral thermal damage during continuous laser processing of CF/PEEK.