Surface Preparation of Alumina for Improved Adhesive Bond Strength in Armor Applications
Surface treatments of alumina have been investigated with the aim of increasing the strength of the bond created between the alumina and a toughened epoxy adhesive. Four surface conditions have been assessed: as-fired; grit blasted; and krypton fluoride excimer laser treated under two sets of conditions. Compared with the as-fired surface, the grit blasted surface was rougher with poorer wettability, probably due to surface contamination. It was found that the laser treatments removed some of the sintering additives and caused rounding of the alumina grains, slightly increasing the surface roughness. Further, the laser treatment led to an increased surface energy and wettability, which has been linked tentatively to an observed increase in the hydroxyl groups on the surface. The adhesive bond strength was assessed by testing joints in tension and shear. It was found that the laser treated surfaces demonstrated slight improvements in bond strength, with a cohesive failure of the adhesive in tension for surfaces subjected to one of the two laser treatments, compared with failure at the interface for the as-fired, grit blasted and other laser treated samples in tension and for all samples in shear. Thus, it has been demonstrated that modifications to the surface of alumina can result in mechanical and chemical changes which affect roughness, wettability, bond strength and the locus of failure.
Excimer laser surface modification of engineering ceramics for adhesive bonding
Abstract The surfaces of two engineering ceramics, LT35 (TiC + Al2O3) and Si3N4 were irradiated with a high power KrF Excimer laser. The effect of laser pulse frequency, energy intensity and number of pulses upon the surface morphologies and roughness were examined. Conical structures on the treated surfaces were observed after the laser treatment. The ablation depths were found to be dependent upon the type of ceramics and laser processing parameters. The treated surfaces were adhesion bonded using a toughened epoxy resin adhesive. Significant improvement in adhesion shear strength of the bonded specimen with laser-treated surfaces were achieved as compared with those specimen with surfaces in the as-received, SiC-paper-abraded and sand-blasted conditions.
Characterization of surface pretreatments of carbon fiber–polyimide matrix composites
Various surface pretreatments of carbon fiber–polyimide matrix composites have been studied by XPS, ISS, PASFTIR (photoacoustic Fourier transform infrared spectroscopy) and high-resolution SEM. Reduction of fluorocarbons from release cloth contamination and increase in carbon–oxygen-containing functional groups was observed on the surface of composite samples treated in an oxygen plasma. These plasma-treated samples also showed differences in surface topography, but no change in the photoacoustic infrared spectra when compared to a methanol-washed sample.