Influence of femtosecond laser marking on the corrosion resistance of stainless steels

Marking is of prime importance in the field of biomaterials to allow the identification of surgical tools as well as prostheses. Nowadays, marking is often achieved by means of laser beam, which may modify the characteristics of the treated surfaces. The use of laser devices delivering nanosecond pulses is known to induce dramatic corrosion degradations during sterilization or decontamination processes of the biomaterials. The aim of the present study is to investigate the ability of femtosecond (pulse duration in the 10 15 s range) laser treatments to avoid preferential corrosion processes of the marked areas, in order to extend the durability and the reliability of biomaterials. Experiments have been performed on martensitic Z30C13 and austenitic 316L stainless steels. Electrochemical measurements (cyclic polarization curves) were carried out to determine the passive state of samples before and after engraving, their corrosion rate and their susceptibility to localized corrosion. Further protracted immersion tests were also carried out to evaluate the natural long-term degradation of engraved parts. The electrochemical behavior is then explained on the basis of surface characterizations. Femtosecond laser marking is shown to provide an electrochemical ennoblement. Moreover, the chemical composition is not affected so that the passive character of both stainless steels is maintained, even improved if we consider the susceptibility to localized corrosion.