Hydrogen embrittlement in Ti–6Al–4V: A comparative review of conventional and additive manufacturing

As hydrogen (H) plays an increasingly central role in clean energy technologies, concerns about hydrogen embrittlement (HE) are drawing greater attention. At the same time, additive manufacturing (AM) is gaining momentum as a method for producing end−use components. Among the materials commonly used in AM, Ti–6Al–4V stands out for its high strength−to−weight ratio, excellent corrosion resistance, and suitability for cost−efficient fabrication of complex parts. Nevertheless, exposure to H makes the alloy susceptible to HE, primarily through hydride formation and cleavage. AM processing and its intrinsic thermal cycles alter the microstructure of Ti–6Al–4V compared to conventional manufacturing (CM). These microstructural differences affect H interaction and hydriding behavior, effects further intensified by AM−induced defects and a higher density of α/β interphase boundaries. Assessing the influence of H on these altered microstructures is important to ensure the reliability of AM components. This review addresses a key gap by providing a comprehensive comparison of HE in CM and AM Ti–6Al–4V, summarizing key findings on H uptake, diffusion and trapping, and the predominant HE mechanisms. • Hydrogen embrittlement is altered by additive manufacturing (AM) routes. • Continuous β in electron beam powder bed fusion accelerates hydrogen (H) diffusion. • α′ martensite promotes early hydride precipitation and cracking. • Key gaps remain on H–microstructure, defect interactions, and fatigue. • More studies in multiscale modelling of H embrittlement in AM Ti–6Al–4V are needed.