Adhesive Failure of Epoxy-Titanium Bonds in Aqueous Environments

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Abstract
Plane-strain adhesive failure tests have been conducted on adhesive joints established between an epoxy resin and untreated titanium metal. The tests were carried out both before and after immersion of the specimens in water, at different temperatures and pH values as well as for different times. Using a suitable mathematical analysis, these data provide the cohesive or adhesive failure energy of the system as a function of crack propagation speed. Generalized fracture mechanics theory can then be used to separate the contributions to the total failure energy arising from mechanical hysteresis and interfacial energy respectively. It is found that the interfacial binding energy, θo. decreases with the time of immersion according to a first-order chemical reaction with a rate constant which increases with the hydrogen ion concentration. The initial (dry) binding energy is approximately ten times the Van der Waals interaction energy but decreases after long times of immersion to a value about equal to this interaction energy. A probable mechanism is the acid hydrolysis of ether linkages between the epoxy resin and the titanium oxide surface.

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