Abstract

This study concerns the structural modifications of metallic alloys such as aluminum alloys, titanium alloys and steels in order to improve their mechanical and physic-chemical properties. These modifications induce changes in the lifetime of these metallic samples as far as the corrosion resistance is concerned. Effects have been studied as a function of incident energy density, overlapping, number of pulses using a KrF excimer laser (20 ns; 80 W; 248 nm). Structural modifications analysed by low-incidence X-ray diffraction have been observed for all materials with micro and nano-structures formation due to the high values of the cooling rate (>10⁸ K.s⁻¹). The most interesting structures were, for instance, the titanium Ti6Al4V (α+β) which after processing becomes a fine lath martensitic structure which has a thickness of approximately of 250 nm, and also steel 35NCD16 (ferrite+perlite) which is austenitic+martensitic after treatment. An investigation was carried out after scanning large surfaces into corrosion resistance of these metallic materials. Electrochemical tests -anodic polarisation- revealed a significant increase in the resistance to pitting of the aluminum alloys. This improvement is due to the dissolution of khatyrkite phase in the matrix leading to a redistribution of the copper atoms within the melted layer (few microns). On the other hand, 2017A aluminum can be slightly softened by the processing. In the opposite, for other materials a hardening can occur. This hardening can be weak and due to a simple grain refinement, as is the case for the 1050A aluminum. This hardening is significant when treating the Ti6A14V titanium and even more so for the 35NCD16 steel which goes from 250HV to almost 1000HV, which is impossible to obtain with classic thermal processes. In the case of 35NCD16 steel samples, the gain in the corrosion resistance is due to change in the structure and due to a galvanic coupling between the irradiated and the non irradiated zones.

© 1996 IEEE