Preliminary investigation on selective laser melting of Ti-5Al-2.5Sn α-Ti alloy: From single tracks to bulk 3D components

In the present work, selective laser melting of Ti-5Al-2.5Sn α-Ti alloy has been carried out on a self-developed system. First of all, optimized processing parameters for 3D Ti-5Al-2.5Sn components were determined through single track and single layer formation processes. After that, near full-dense parts with different sizes were successfully built up and their microstructures as well as texture features were in-depth analyzed employing optical microscope, scanning electron microscope, transmission electron microscope, X-ray diffractometer and electron back-scattered diffraction. Because of the rapid cooling rate inherent to selective laser melting technology and the absence of β-stabilizing elements, as-deposited Ti-5Al-2.5Sn possesses an overwhelmingly acicular α′ martensitic structure with a small amount of α grains discontinuously precipitated at the prior-β grain boundaries, making it exhibit higher strength/hardness but poorer elongation/impact toughness in comparison to the deformed and as-cast Ti-5Al-2.5Sn. The overall texture is found to be nearly random after SLM. As a result, mechanical behaviors of the as-built Ti-5Al-2.5Sn are isotropous. Under the interaction between the residual pores and the overwhelmingly martensitic microstructure, as-deposited sample presents better fatigue performance than the forged Ti-5Al-2.5Sn at a high peak cyclic stress of beyond 700 MPa. Nevertheless, the opposite situation occurs when the peak cyclic stress is lower than 700 MPa.