Micro-arc oxidation process of the porous titania coating on titanium alloy produced by selective laser melting

Abstract

Selective laser melting (SLM) has been developed rapidly in recent years as a kind of additive manufacturing technology. Normally, titania coating containing Ca and P elements was fabricated on titanium alloy by micro-arc oxidation (MAO) to improve the superficial bioactivity of it. The microstructure, thickness and phase component of the coated samples were investigated by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The results show that with the increase of oxidation time, the size of the micro-pores increase, the content of elements Ca and P increase firstly and then decrease in the coating. The MAO coating is mainly composed of rutile and anatase, with increasing of oxidation time, the contents of rutile increase. The corrosion behavior of all the samples was examined by potentiodynamic polarization in SBF solution. The MAO-treated sample has the best corrosion resistance with the lowest corrosion current density and the highest electrochemical impedance. Incubated in a simulated body fluid after 14 days, bone-like hydroxyapatite (HA) was completely formed on SLM-produced TC4 alloy after MAO-treatment, thus evidencing preferable bioactivity. All outcomes are attributed to MAO as a post-treatment process of titanium alloys prepared by SLM for medical application. In addition, acicular α’ martensite produced in the forming process of SLM could produce more discharge channels as well as accelerating the chemical reaction and element diffusion during the micro-arc oxidation process. So the surface micro-pores of the coating increased in number but decreased in size. Simultaneously, active elements entering the coating would slightly increase.