Optimisation of wet chemical silane deposition to improve the interfacial strength of stainless steel/epoxy

Highlights: • γ-aminopropyltriethoxysilane (APS) wet surface treatment was evaluated to improve the interfacial strength of stainless steel/epoxy hybrid. • The applied methodology seems to be of major importance. • A doubling of the interfacial strength compared to non-treated samples is observed. • The obtained fracture strength value of more than 60 MPa by far exceeds values currently found in literature and approaches the epoxy fracture strength. - Abstract: The evaluation of various wet chemical deposition conditions of γ-aminopropyltriethoxysilane (APS) on stainless steel resulted in stainless steel/epoxy hybrids with improved interfacial strength. Nuclear magnetic resonance spectroscopy (NMR) revealed the working window of the silane solution used, while scanning electron microscopy (SEM) and spectroscopic ellipsometry (SE) served at characterising the final APS film structural properties. With pull-off testing the interfacial strength of surface treated steel plates in contact with an epoxy resin was determined. Fracture surface morphological features allowed identifying the failure mode. Optimisation of the different silane deposition conditions led to a doubling of the interfacial strength compared to non-treated samples. The fracture strength value of more than 60 MPa by far exceeds values currently found in literature and approaches the epoxy fracture strength by which the original adhesive failure mode converts into a more cohesive failure mode