Electrochemical and mechanical behavior of laser processed Ti–6Al–4V surface in Ringer’s physiological solution

Abstract

Laser surface modification of Ti–6Al–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–6Al–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 physiolog- ical solution were evaluated by employing both potentio- dynamic polarization and electrochemical impedance spectroscopy (EIS) methods. The potentiodynamic polar- izations showed an increase in the passive current density of Ti–6Al–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/mm 2 . 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 9 10 3 to 4.38 9 10 5 X cm 2 with increasing laser power densities. However, the magnitudes remain lower than that of the untreated Ti–6Al–4V at OCP. The average hardness and modulus of the laser treated Ti–6Al–4V, evaluated by the nanoindentation method, were deter- mined 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–6Al–4V were *4.1 (±0.62) and *148 (±7) GPa respec- tively. 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.