Influence of Power and Frequency in the Femtosecond Laser Texturing of Ti6Al4V

Abstract

Laser Surface Texturing (LST) has demonstrated to be the most reliable technique for the micro-modification of surfaces, allowing to obtain taylored surfaces. These modifications, depending on the basic micro-geometry and its repetition pattern, can provide special functionalities to a surface, such as hydrophilicity, hydrophobicity, reflectance, anti-bacterial, ostheo-integrability, as well as custom aesthetic, among others.Nevertheless, when a laser irradiates metallic surfaces, the micro-structure can be modified due to the heat induced, changing the mechanical properties of the surface. To avoid these effects, cold or ultra-short pulsed lasers must be used.A cold laser emits optical pulses with a duration below 1 ps (ultra-short pulses), in the domain of femtoseconds (fs=10-15 s). These ultra-short pulses, combined with high frequencies, in the megahertz region, leads to pulse trains with high repetition rates. This allows the sublimation of the material, keeping it relatively cold due to the short exposition time to irradiation.Ti6Al4V is the most used Ti alloy, thanks to its excellent weight/mechanical properties ratio. Nevertheless, its tribological behavior is very poor. Although there is intense research to improve it by using LST, the study of the influence of femtosecond laser parameters in the desired micro-geometries is still a gap in the scientific literature.In this research, a study of the influence of power (up to 50 W) and frequency (up to 2 MHz) in the fs-laser texturing of Ti6Al4V is presented. Local pulse repetition, linear and surface textures have been studied by combining power and frequency in these ranges, evaluating the geometry obtained by variable focus microscopy. The study carried out has allowed to determine the optimal set of parameters as a function on the target texture geometry, as well as the range in which the LST removal process changes from sublimation (for texturing) to melting (for micro-machining).