# Effect of Laser Treatment on Intrinsic Mechanical Stresses in Titanium and Some of Its Alloys
Thus, the laser treatment enhanced the transformation of Ti and Ti\({}_{2}\)O\({}_{3}\) into TiO\({}_{2}\) within the surface layer [16]. The osteogenic activity expressed by cell proliferation and differentiation was shown to be improved by the femtosecond laser, the effect attributed to reduced Young's modulus and the microhardness of titanium due to an appearance of voids on the subsurface layer, which originated from cavitation during conditions of high tensile stresses and temperatures [23]. The considerable absence of torque after osseointegration was observed for the titanium alloy treated using laser techniques [22]. However, in [11], for the nanostructured titanium surface coated with either TiNbN or subjected to titanium plasma spraying, all implants were osseointegrated and there were noted differences in both the pull-out force and in the bone-tissue volume ratio between irradiated and non-laser-treated specimens. On the contrary, for a few different studies, higher bone-implant contact (BIC) relative values and removal torque values were reported [23]. Cell activity was reduced and cell proliferation retarded on a surface with a superhydrophobic angle and Sa of 10.96 \(\upmu\)m [16]. The generated-by-laser topographical changes optimized the protein-absorption process [24]. The bioactivity expressed by the apatite-forming ability in immersion tests in the simulated body fluid was ameliorated by Yb fiber laser treatment in wet conditions [25]. The antibacterial effect was observed several times for laser-treated titanium. For the femtosecond laser and LIPSS approach, the anti-adhesive properties of _Porphyromonas gingivalis_, _Streptococcus mutans_, and _Porphyromonas gingivalis_ were observed [26]. Moreover,the authors claimed that, simultaneously, the modified surface improved the adhesion of gingival tissue. The use of the DLIP technique with several lasers working together can adjust the surface topography and manipulate osteoblasts and bacteria attachment [2; 3]. So far, the research has focused on the influence of laser treatment on different process parameters, such as laser power, continuous or pulse modes, and scan rate, on the surface characteristics. The studies have almost been exclusively limited to titanium and Ti6 Al4V alloys. This study investigates whether and to what extent the chemical and phase compositions of laser-processed titanium substrate affect the mechanical properties and residual stresses within the surface layer, an issue not often investigated. Titanium and two of its alloys were tested, after laser processing, and heat-treated after laser melting. The roughness, hardness, and intrinsic stresses at different distances from the surface were measured. The previous measurements [27] were performed on similar materials demonstrating that high tensile stresses are obtained in the surface layers after short-pulse laser treatment. In these studies, the materials used--titanium alloys Ti7 Nb6 Al and Ti15 Mo--are a novelty. The obtained results confirm the formation of tensile stresses in the layers remelted with the Nd:YAG laser.