Hydrogen effects on electrochemically charged additive manufactured by electron beam melting (EBM) and wrought Ti–6Al–4V alloys

Abstract

The hydrogen behavior in electrochemically charged electron beam melting (EBM) and wrought Ti–6Al–4V alloys with a similar β-phase content of ~6 wt% was compared. Hydrogenation resulted in the formation of microvoids, either adjacent to the surface or along interphases, their coalescence, and emanation of microcracks around them. The microstructure of the EBM alloy displayed a discontinuous arrangement of β-phase particles in the short-transverse direction, a smaller lattice constant of the β-phase, and more α/β interphase boundaries, making the EBM alloy more susceptible to hydrogen embrittlement. The hydrogenated alloys were composed of αH (hcp) and βH (bcc) solid solutions as well as δa (fcc) and δb (fcc) hydrides with lattice parameters that have not been reported before. These hydrides were transformed from the primary α-phase. No major microstrain difference was observed between the EBM and wrought alloys, either before or after hydrogenation. Microstrains in the α and β phases increased following hydrogenation; they were larger in the βH and δa phases compared to the αH and δb phases. A post-treatment that would increase the size of the β particles is suggested to improve the resistance of EBM Ti–6Al–4V to hydrogen-induced damage.