Electrochemical and mechanical behavior of laser processed T1-6A1-4V surface in Ringer's physiological solution

摘要

Laser surface modification of Ti-6A1-4V with an existing calcium phosphate coating has been conducted to enhance the surface properties. The electrochemical and mechanical behaviors of calcium phosphate deposited on a Ti-6A1-4V surface and remelted using a Nd:YAG laser at varying laser power densities (25-50 W/mm~2) have been studied and the results are presented. The electrochemical properties of the modified surfaces in Ringer's physiological solution were evaluated by employing both potentio-dynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The potentiodynamic polarizations showed an increase in the passive current density of Ti-6A1-4V after laser modification at power densities up to 35 W/mm~2, after which it exhibited a decrease. A reduction in the passive current density (by more than an order) was observed with an increase in the laser power density from 25 to 50 W/mm2. EIS studies at the open circuit potential (OCP) and in the passive region at 1.19 V showed that the polarization resistance increased from 8.274 × 10~3 to 4.38 × 10~5 Ω cm~2 with increasing laser power densities. However, the magnitudes remain lower than that of the untreated Ti-6A1-4V at OCP. The average hardness and modulus of the laser treated Ti-6A1-4V, evaluated by the nanoindentation method, were determined to be 5.4-6.5 GPa (with scatter <±0.976 GPa) and 124-155 GPa (with scatter <±13 GPa) respectively. The corresponding hardness and modulus of untreated Ti-6A1-4V were ～4.1 (±0.62) and ～ 148 (±7) GPa respectively. Laser processing at power densities >35 W/mm~2 enhanced the surface properties (as passive current density is reduced) so that the materials may be suitable for the bio-medical applications.