The Stability of Different Titanium-PEEK Interfaces against Water

Fibre Metal Laminates (FML) consisting of alternating stacked layers of polymer matrix composites and metallic foils are considered for structures with high fracture toughness and good impact resistance in aeronautic applications. The properties of thermoplastic Fibre Metal Laminates composed of titanium and carbon fibre reinforced polyetheretherketone (Ti/CF-PEEK laminates) are under investigation at DLR. The adhesion between the polyetheretherketone (PEEK) matrix and titanium degrades by the influence of humidity. Physical, chemo-physical and chemical surface pre-treatments of the titanium layers were tested to improve the long-term behaviour of the interface. To compare the different surface treatments, lap shear specimens were prepared and partly exposed to hot water (80 °C). Lap shear tests were conducted to determine the degradation of the initial strength by the influence of water. Concerning the physical pre-treatment, the laser pre-treatment offers the highest magnitude of humidity resistance because of the magnitude and kind of surface roughness. Concerning the chemo-physical pre-treatment, the anodization offers reduced initial bonding strength and reduced humidity resistance caused by the created oxide layer. Concerning the chemical pre-treatment, the usage of adhesion promoter causes enhanced initial bonding strength but also reduced humidity resistance.