Influence of Microstructure and Surface Roughness on Oxidation Kinetics at 500–600 °C of Ti–6Al–4V Alloy Fabricated by Additive Manufacturing

Abstract

Ti--6Al--4V alloy (TA6V) is the most commonly used titanium-based alloy and is usually manufactured by casting, forging or rolling. Additive manufacturing is a new way of processing metal alloys; it is currently used for production purposes. This study focuses on the microstructure and oxidation kinetics of Ti--6Al--4V fabricated by laser beam melting. Some samples were HIP-treated (hot isostatic pressure). Ti--6Al--4V rolled and annealed was used as a reference material. Ti--6Al--4V fabricated by LBM exhibited prior $\beta$ grains elongated in the building direction with fully acicular martensite, $\alpha${\textasciiacutex}. Isothermal oxidations were performed at 500, 550 and 600Â {\textdegree}C for durations of 100, 200 and 500Â h. The oxidation kinetics followed a parabolic law. The weight gain of as-built LBM samples was twice as high as that of ground LBM samples of Ti--6Al--4V, although both sets had the same oxide layer thickness and depth of oxygen diffusion in the alloy. Ground LBM samples presented an oxidation rate close to that of conventional rolled and annealed Ti--6Al--4V alloys. It was shown the higher weight gain of LBM-produced Ti--6Al--4V samples was mainly due to their higher specific area and to the oxidation of partially melted powder on their surface.