Heat treatments effects on functionalization and corrosion behavior of Ti-6Al-4V ELI alloy made by additive manufacturing

Abstract

Additive manufacturing has emerged in recent years as one of the most in-demand technology for manufacturing of prototypes and components with complex geometries. Its application in biomedicine shows a big productive potential concerning customized implants with optimized geometries, reducing risks of rejection and achieving better ergonomic results. However, Ti-6Al-4V ELI pieces produced by Direct Metal Laser Sintering (DMLS) need a post heat treatment in order to reach optimum mechanical properties as well as to release internal stresses resulted from the manufacturing process. This study aims at analyzing the change of microstructure in DMLS samples by effect of heat treatments and its influence in the corrosion behavior and in the anodizing process. The surfaces were analyzed by 3D confocal profilometry, scanning electron microscopy and energy dispersive X-ray spectroscopy. DMLS samples showed different microstructures after heat treatments in the range from 650 to 1050 °C. The main difference in the microstructures is the nucleation and growth of β phase, which could have a detrimental effect on its corrosion behavior. The corrosion behavior was studied by cyclic potentiodynamic polarization in phosphate buffered saline solution at 37 °C. After anodizing, an oxide film was grown on the material surface, composed of a barrier and a nanoporous layer doped with F ions. The passive current density was reduced by approximately two orders of magnitude for all conditions, despite morphological differences on the layers. This is not only an improvement of the corrosion resistance but also a decrease in the ion release into bloodstream.