Laser-assisted thermochemical ultrahigh-precision polishing of titanium in phosphoric acid solution

Abstract

Surface finish is one of the most important quality characteristics of titanium implants in the medical field. In this paper, a laser-assisted thermochemical polishing system based on scanning galvanometer was designed and built for the ultrahigh-precision polishing of titanium. The influence of the laser processing parameters and initial surface roughness of the workpiece on the final polishing results were systematically studied, and the polishing mechanisms were discussed. The results show that the final polishing quality was closely related to the laser pulse energy, spot overlapping rate, scanning times, and properties of the material itself but not to the initial surface roughness of the workpiece. In addition, the laser destroyed the passivation layer on the surface of the workpiece, resulting in direct contact between the titanium and etching solution. On the other hand, it induced the generation of a thermo-electromotive force, which caused the electrochemical corrosion on the workpiece surface, accelerating the dissolution of peaks on the surface of the material. The workpiece surface finish was improved because of the difference between the material dissolution rates of the peaks and valleys. Finally, ultrahigh-precision polishing of a commercially pure titanium surface was achieved using the optimized process parameters.