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

The hydrogen behavior in electrochemically charged electron beam melting (EBM) and wrought Ti-6Al-4V alloys with a similar beta-phase content of similar to 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 beta-phase particles in the short-transverse direction, a smaller lattice constant of the beta-phase, and more alpha/beta interphase boundaries, making the EBM alloy more susceptible to hydrogen embrittlement. The hydrogenated alloys were composed of alpha(H) (hcp) and beta(H) (bcc) solid solutions as well as delta(a) (fcc) and delta(b) (fcc) hydrides with lattice parameters that have not been reported before. These hydrides were transformed from the primary alpha-phase. No major microstrain difference was observed between the EBM and wrought alloys, either before or after hydrogenation. Microstrains in the alpha and beta phases increased following hydrogenation; they were larger in the beta(H) and delta(alpha) phases compared to the alpha(H) and alpha(b) phases. A post-treatment that would increase the size of the beta particles is suggested to improve the resistance of EBM Ti-6Al-4V to hydrogen-induced damage. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.