Comparative Study of Resin and Silane Coupling Agents Coating Treatments on Bonding Strength Improvement of Titanium and Carbon Fiber Composites

In this study, anodizing treatment was utilized to etch titanium (Ti) substrates’ surface to prefabricate nano-cavities. Resin pre-coating (RPC) and three silane coupling agents’ coating (CAC) techniques were further applied to porous Ti substrates surface to compare the reinforcement effect of adhesive bonding strength. SEM images show that nano-cavities have been prepared to create a greater contact area and vertical volume on Ti substrate surface, fully covered by resin coatings via RPC. A higher surface roughness and better surface wetting are also obtained by the testing results of atomic force microscope and contact angles. Single lap shear tests results indicate that specimens with “anodizing + RPC” treatment yield the best average shear strength of 20.73 MPa, increased by 31.7% compared to anodizing base strength and at least 63.0% higher than silane KH-550/560/792-coated specimens. A dominant cohesive failure and fiber-tearing on CFRP’s shallow surface, instead of adhesive debonding failure, are shown in the appearances of damaged specimens, proving that the RPC technique has a more effective bonding strength reinforcement in titanium and carbon fiber-reinforced polymer (Ti-CFRP) composites’ toughening. Thus, the simple RPC technique can be regarded as a new-type alternative to adhesive joint toughening to manufacture high-performance composites for aerospace applications.