Corrosion and corrosion-fatigue behavior of cp-Ti and Ti-6Al-4V laser-marked biomaterials.

The aim of this work was to determine the influence of laser surface modification treatments on mechanical and electrochemical behavior in Ti and Ti-6Al-4V implants. For each metal, different samples were laser modified simulating the markings according to the international requirements. (It is necessary in each metallic biomaterial to mark the serial, batch and company numbers.) Microstructural changes produced by this treatment were observed: (a) the melting zone with small grain sizes and martensitic structures in above-mentioned metals and (b) the heat-affected zone (HAZ) with alpha phase in cp-Titanium with bigger grain sizes and Widmanstatten structure in Ti-6Al-4V. Positive tensile residual stress was determined by means X-ray analysis in the zones marked by laser. Furthermore, corrosion behavior was studied in a simulated body fluid at 37°C. Pitting was observed in different zones near the HAZ and the results showed a decrease of the corrosion resistance in the laser treated samples. Residual stresses and the martensitic microstructures favoured the decrease of the corrosion-fatigue life around 20% of both metals under physiological conditions.