Abstract
Profiting the economic and ecologic benefits of additive manufacturing (AM), titanium becomes attractive to extend its application potential as it possesses excellent mechanical properties and a high corrosion resistance. However, AM processing entails typical AM features including residual thermal stresses, pores, anisotropy and the presence of a martensitic α’ phase due to the high cooling rate and the intrinsic building process affecting the microstructure. Since the sensitivity to hydrogen embrittlement is associated to these microstructural features, knowledge is necessary on the hydrogen-metal interaction of these AM characteristics. Therefore, this research aims to investigate the difference in hydrogen-metal interaction between conventionally cold rolled and AM laser powder bed fused Ti‑6Al‑4V. A higher mechanical strength is obtained for the AM specimens due to the presence of the martensitic α’ phase. After electrochemical hydrogen charging, the resistance to hydrogen embrittlement is assessed by in-situ constant extension rate testing. As a consequence of the low hydrogen solubility in α’ of AM Ti-6Al-4V, hydride formation is observed in the neighbourhood of the crack tip, as verified by SEM‑BSE and XRD. It suggests that the stress induced hydride formation mechanism is acting. Meanwhile, the hydrogen embrittlement in conventionally cold rolled Ti-6Al-4V is dominated by hydrogen enhanced localised plasticity (HELP), facilitated by a higher hydrogen solubility in its α-β microstructure. Furthermore, the porosity of AM material plays a detrimental role in the initiation of failure for the hydrogenated AM Ti-6Al-4V.