Joint strength of Fe/epoxy resin hybrid structure via porous Fe/TiB2 composite layer synthesized by in-situ reaction process

Abstract

• Joint strength of Fe/epoxy resin hybrid structure was investigated. • Fe and epoxy resin were interlocked via an open-cellular Fe-based layer. • Surface roughness and adhesiveness between porous Fe and substrate was important. • The strength was clarified with an interfacial strength estimated from mixture law. • A functionally graded powder condition is effective for high joint strength. Fe/epoxy resin hybrid structures were fabricated via three-dimensional open-cellular porous Fe/TiB 2 composite layers by an in-situ reaction synthesis process. Pores in the porous layer were filled with an epoxy resin to form an interpenetrating phase layer (IPL) consisting of epoxy resin and Fe/TiB 2 composite. The relationship between the tensile joint strength perpendicular to the joint interface and structures of the porous layer was investigated. The tensile joint strength increased with increasing the roughness of an end surface of the porous layer but decreased when the surface roughness was higher than approximately 30 μm. The decrement in the joint strength was caused by a transition of the fracture position from an epoxy resin/IPL interface to Fe/IPL interface due to poor adhesiveness of the porous layer/Fe interface. A high-resolution X-ray computed tomography (CT) was utilized for investigating change in area fraction of the epoxy resin with depth from the end surface of the IPL. Based on the X-ray CT and fractography, it was revealed that the joint strength could be understood in view of epoxy resin/IPL interfacial strength at the fracture position estimated from the mixture law when the adhesiveness of the porous layer/Fe interface was enough. Based on the results above, an in-situ reaction induced from a functionally graded powder condition was applied for enhancing joint strength.