Adhesion studies of radio-frequency sputtered SiO2 films on Ti,stainless steel,Ni and Inconel substrates. Effects of substrate surface ion bombardment etching

The scratch test was applied to determine the adhesion strength of radio-frequency (RF) sputtered SiO₂ films to Ti, stainless steel, Ni and Inconel substrates. The effect of substrate ion bombardment etching was investigated by using a mean critical load derived from a Weibull-like statistical analysis. It was found that the mean critical load values obtained on substrates etched by ion bombardment for a sufficiently long time were two to three times those obtained on mechanically polished substrates. Scratch tracks were observed by scanning electron microscopy and some X-ray spectra were measured after the electron beam of the scanning electron microscope was focused inside the scratch channel. Depth composition profiles were also recorded by Auger electron spectroscopy. No important presence of contamination was observed in the interfacial domain even after mechanical polishing, but the width of this interfacial domain was higher after ion bombardment than after mechanical polishing. This difference in width could result from the formation of microcavities and vacancies at the substrate surface during ion bombardment. In such a case, the significant adhesion improvement should principally occur from an enhanced interlocking of the coating to its substrate.