Hybrid Material Systems - Characterization of Titanium-PEEK bonding interfaces

Due to steadily increasing complexity and requirements for aircraft components, the materials’ choices are usually compromises. Combining different materials to a hybrid material system, the advantages of each constituent can be overcome by exploiting the properties of the other constituents. Fiber Metal Laminates (FML), composed of alternating stacked layers of metallic foils and Polymer Matrix Composites (PMC), combine the advantages of PMC and metals. Thus, FML offer a properties profile superior than their individual constituents, i.e. high resistance against crack growth, good impact properties, high fracture toughness and improved corrosion behavior. Further advantages arise if thermoplastics are used as PMC-matrix, e.g. thermal formability and weldability. However, thermoplastic-based FML are a particular challenge for adhesive bonding: like all hybrid materials, they require long-term stable metal-polymer interfaces. The understanding of the bonding and degradation mechanisms is a prerequisite to design and produce degradation resistant bonds. In this work, the interface between the titanium alloy Ti-3Al-2.5V and carbon fiber reinforced Poly-ether-ether-ketone (CF/PEEK) is investigated in a TiGr FML. This study focuses on the laser pre-treated Ti-3Al-2.5V surface, the joining process and the PEEK properties at the Ti-3Al-2.5V/PEEK interface. Mixed mode bending experiments in conjunction with Raman spectroscopy, secondary electron-, analytical transmission electron- and confocal laser scanning microscopy indicate that good interface adhesion is caused by a combination of mechanical interlocking at the nanoscale and chemical interactions, which are evidenced by massively enhanced interfacial crystallization in the PEEK near the Ti-3Al-2.5V surface