Joining of carbon fiber reinforced polymer/titanium stacks using directed energy deposition additive manufacturing

In this work, we successfully fabricated CFRP/Ti stacks with reliable interfacial bonding using the directed energy deposition (DED) additive manufacturing (AM) technique. Compared to traditional laser welding, the DED process can produce a smaller penetration depth due to the ejection of feedstocks into the melt pool. Such an additive process also enables the multilayer deposition of three-dimensional (3D) Ti alloys with a designed structure to coalesce with the CFRP plate. This study utilized numerical modeling and experiments to uncover the interface formation mechanisms and bonding performance of CFRP/Ti stacks fabricated at different laser powers. The cross-sectional morphologies of CFRP/Ti stacks were observed by an optical microscope (OM) and a scanning electron microscope (SEM). Physical gaps and pores existed along CFRP/Ti interface and within CFRP substrates, respectively. The bonding performance of overall CFRP/Ti stacks was also assessed by lap shear tensile testing. The lap shear tensile strength increased first and then decreased with laser power. The fracture failure of CFRP/Ti interface was characterized by a SEM and X-ray photoelectron spectroscopy (XPS), which indicated the mixed adhesion and cohesion failure mode of DED-joint stacks. This work provides a novel CFRP/Ti stack joining paradigm through DED, paving the way for AM of multi-material lightweight components.