Hard coating adhesion on ion implanted polymer surfaces

Modern plastics are of great importance in many practical applications and their performance can be enhanced by surface modification to improve their hardness, wear and chemical resistance. Metallic coatings, in particular hard Cr, have been successfully deposited by various techniques; unfortunately, the low polymer surface tension opposed to the high intrinsic stresses of the coatings often gave adhesion problems. The conventional pre-treatment of polymers in view of metallization is based on hazardous and pollutive agents. We used a combination of ion implantation and vapor deposition (performed in the same chamber) allowing for the production of well adherent coatings. Nf ions were implanted at medium-low doses on polycarbonate substrates. Following ion irradiation, chromium films were deposited by evaporation. The implanted substrates were characterized with respect to their structure by Raman spectroscopy, wettability and nanohardness. The mechanical properties of the coatings were examined as a function of the ion beam treatment. The coatings were characterized with respect to morphology, scratching resistance as well as nanohardness. It was observed that, without the ion pre-treatment, the coatings were poorly adherent. Due to the high level of stresses developed in the Cr layers, the coatings on unimplanted samples appeared broken, as expected. On the contrary, the adhesion of the coatings was appreciably better for the pre-implanted specimens. This was certainly due to the superior mechanical properties exhibited by the implanted polymers as well as to enhanced wettability induced by energetic ion bombardment. Scratch tests showed an optimized tribological behavior for the ion implanted/coated polymer surfaces. (C) 2000 Elsevier Science B.V. All rights reserved.