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The nature of the oxide on the surface of titanium and the Ti-6Al-4 V alloy after a number of recommended treatments has been examined by x-ray and electron diffraction. No evidence for material other than titania in its rutile form was obtained even though anatase and fluoride have been reported. The most efficient surface for adhesive bonding is a rough surface of the black oxide such as is produced by treatment of the metal in alkaline hydrogen peroxide.

Surface pretreatments affect joint strength, some improve it, e.g. etching in aqueous hydrofluoric acid or oxidation in alkaline hydrogen peroxide; while others decrease the strength e.g. etching in acids containing high concentrations of oxidising agents. For Ti-6A1-4V alloy, best results are obtained by either etching in aqueous hydrofluoric acid or oxidation in alkaline hydrogen peroxide for about two hours. The results indicate that a pretreatment which leaves a coherent TiO2-rutile layer, on a rough surface, form the strongest joints. Surface roughness is shown to enhance bond strength.

Torsional shear napkin-ring test-pieces have been used in adhesion studies with two titanium alloys, modified epoxy and epoxy-phenolic adhesives. The temperature profiles have been obtained and the failure surfaces studied. The metallography of the surfaces is recorded and the effect of a variety of preparative surface treatments. Most treatments lead to rutile, and in one case rutile needles bond to the adhesive more strongly than to the substrate. Surface roughness is shown to enhance bond strength.