Search

This work reports a systematic and quantitative evaluation of the effects induced on the adhesive properties of carbon fiber reinforced polymer (CFRP) substrates by various vacuum cold-plasma treatments. In particular, surface activation of the CFRP substrates was performed using several combinations of exposure time, plasma power, and processing gas (air, O-2, Ar and N-2). By comparing these plasma treatments with conventional techniques of abrasion and peel ply, it was possible to substantially increase the performance of the adhesively bonded joints made by overlapping the CFRP substrates with a structural epoxy resin. On each differently treated surface, measurements of roughness and of wettability were performed, allowing the evaluation of the increase in surface energy after the plasma treatment. XPS analyses allowed the identification of the chemical state of the substrates and showed an in-depth functionalization of the outer layer of the CFRP material. The experimental results show that an engineered plasma treatment of the CFRP substrates allows one to modify the surface morphology and both wetting and chemical activation properties of the treated surfaces, resulting in an increased mechanical shear strength of the joints.

This paper deals with the interfacial adhesion properties of Ti-6Al-4V alloy substrates, prepared by using different treatment protocols selected on the basis of their different effectiveness, and bonded using a structural, high-strength epoxy adhesive. The alternative pre-bonding treatments were sodium hydroxide anodization and low-pressure-plasma treatment, the effects of which were compared to that of a base preparation via solvent degreasing of the substrates’ surface. The treated surfaces were joined according to standard protocols, and then tested for shear strength. The mechanical results were then correlated to surface characteristics of the substrates such as oxidation state and wettability. Parallel scanning Kelvin-probe measurements allowed us to focus our attention on the possible role of the electrical properties of the substrates. We observed that each treatment entails different behavior of the electrical potential of the surface, which correlates with the mechanical strength of the joints. The results suggest that an evaluation of the surface potential of titanium-alloy substrates might be a promising, indicative supplementary parameter for the evaluation of their pre-bonding surface conditions, allowing correlations with presence/absence of an oxide layer at the resin-substrate interface.

The subject of this paper is the quantitative evaluation of the correlation which exists between the surface characteristics of parts in a titanium alloy, Ti-6Al-4V, and the mechanical strength of the joints, made linking these parts using a structural epoxy adhesive. In particular, the surfaces were prepared by using vacuum plasma as a prebonding treatment with various process gases (air, Ar and O2). For each of these treatments, tests were performed for the mechanical characterisation of the joints, and surveys on the wettability properties were carried out by using a sessile drop method in order to estimate the surface energy of plasma treated surfaces. The results were related to the morphological and electrical properties of the substrates, defined in parallel through SKPM assessment. Further XPS analyses of their chemical state allowed the evaluation of the effect of vacuum plasma on both contaminant removal and formation of a weak oxide layer. The results obtained highlighted interesting relationships between vacuum plasma surface preparation and mechanical resistance of the bonded joints, as well as synergy between the morphological, electrical and chemical properties present in adhesive phenomena.