CHARACTERIZATION OF CARBON AND ZIRCONIA FILMS DEPOSITED ON POLYCARBONATE FOR SCRATCH-PROOF COATING APPLICATIONS

Hard carbon films and tetragonal zirconia films have been deposited on polycarbonate (PC) substrates using RF magnetron sputtering. The stru cture of the carbon films were deduced from X-ray excited Auger electr on spectra (XAES). For the zirconia films, the chemical and phase stru cture were determined by X-ray photoelectron spectroscopy (XPS) and X- ray diffraction (XRD). The residual internal stress and the Young's mo dulus were investigated. The adhesion properties and scratch hardness were studied using the scratch test and scanning electron microscopy ( SEM), for carbon and zirconia films with a comparable stored elastic s train energy. The adhesion failure mechanism appeared of cohesive natu re in carbon/PC systems, while failure in zirconia/PC was due to a hig h internal stress relief. Both kinds of films are found to harden the PC surface, with carbon displaying a greater extent. While the same cr itical load was found for both materials in the single-pass scratch te st, a better performance was shown by the zirconia films in the multi- passes scratch test. A practical work of adhesion of 0.4 J m(-2), calc ulated on the basis of the model developed by Bull et al., was found f or zirconia/PC, while an extrapolated value of 0.03 J m(-2) was obtain ed for the carbon/PC. (C) 1998 Elsevier Science S.A.