Laser-induced surface modification of C/PEKK for co-curing with C/epoxy

Co-curing of thermoplastic and thermoset composites offers an attractive integration route for lightweight aircraft structures. However, achieving a durable interface often relies on extensive surface pretreatments and the use of additional bonding materials at the interface. This work explores the use of laser heating to locally modify the surface of a carbon fiber reinforced polyetherketoneketone (C/PEKK) laminate with the aim of enhancing co-curing with a carbon fiber reinforced epoxy. Central to this approach is the formation of an amorphous surface layer that is more susceptible to interdiffusion during co-curing. High-rate differential scanning calorimetry showed that crystallization of PEKK is suppressed for cooling rates exceeding 10 °C s -1 . Static spot laser heating achieved cooling rates of 100 °C s -1 to 400 °C s -1 , resulting in a locally amorphous surface layer, as confirmed by microscopy and differential scanning calorimetry, along with a minor increase in surface roughness. Laser-treated surfaces were subsequently co-cured with a carbon fiber reinforced epoxy in an autoclave. Energy-dispersive X-ray analysis of cross-sections indicated enhanced interdiffusion across the interface when the thermoplastic surface was rendered amorphous. Mandrel peel testing showed that the treatment resulted in improved interfacial performance compared to an untreated reference and to a surface that was annealed after the laser treatment. Overall, the results demonstrate that laser heating provides a promising route for tailoring thermoplastic composite surfaces prior to co-curing.