Interfacial chemistry of adhesive joint failure: an investigation by small area XPS, imaging XPS and TOF-SIMS

Abstract

The strength and mode of failure of adhesively bonded iron substrates has been investigated. Joints were assembled from polished iron and from iron substrates that had been pretreated in a novel manner by the cathodic deposition of yttrium. Joints were exposed to an aqueous environment and a reduction in joint strength with increasing exposure time was noted. Failure surfaces of joints exposed to water for 1200 and 7500 h were examined by small-area XPS, imaging XPS and TOF-SIMS. An interfacial failure was observed, and although all surfaces were rich in nitrogenous species from the curing agent, no evidence of epoxy residues on the interfacial metal failure surfaces was recorded by TOF-SIMS. The metal failure surface at extended exposure times shows that there are two delamination fronts advancing from the exposed edge of the adhesive joint: one is associated with bond cleavage and gives rise to a ‘zero-volume debond’ and proceeds faster than the other, which is associated with gross separation of the adhesive and substrate, oxide growth on the exposed metal adherend and mass transport within the disbondment crevice.