Effect of microstructural anisotropy and heat treatment on the corrosion behaviour of additively manufactured Ti-6Al-2Sn-4Zr-6Mo alloy

The electrochemical behaviour of Ti-6Al-2Sn-4Zr-6Mo alloy produced by Powder Bed Fusion – Laser Based/Metals has been investigated to identify the corrosion mechanism characteristic of the material processed by additive manufacturing technology. A microstructural characterisation of the material in as-built and heat-treated conditions was carried out to identify the different phases and assess the degree of anisotropy of the additive manufactured material. After that, the corrosion behaviour was studied by potentiodynamic polarisation and electrochemical impedance spectroscopy. Results showed that a homogeneous and compact oxide layer characterises the as-built material due to the presence of a finely dispersed alpha’’ phase in the beta grains. Conversely, in the heat-treated alloy, the corrosion attack proceeds preferentially on the large alpha phase domains, where the oxide layer is less protective. Despite the anisotropy in the microstructure of the as-built material, the electrochemical behaviour was revealed to be the same for the section parallel and perpendicular to the building direction, noting the less influential factor of grain orientation on corrosion mechanisms.