An atom probe tomography approach to distinguish weak and strong hydrogen traps in alloys

Hydrogen ingress into metals and alloys, particularly high-strength steels, can cause hydrogen embrittlement and threaten structural reliability in hydrogen production, transport, storage and use. Mitigation strategies often rely on hydrogen traps, but their effectiveness depends on trap strength. Here we show that comparison between cryogenic atom probe tomography (cryo-APT) and vacuum-desorption APT enables qualitative differentiation of weak and strong hydrogen traps. Cryo-APT preserves hydrogen at both weak and strong traps after charging, whereas controlled vacuum desorption preferentially removes weakly trapped hydrogen before APT analysis. Using cold-drawn pearlitic steel as a demonstration system, we show that comparison of cryo-APT and vacuum-desorption APT datasets enables spatially resolved inference of trap strength: strained interfaces that retain hydrogen after desorption are identified as strong traps, whereas defects that lose hydrogen are defined as weaker traps. This comparative approach provides a practical framework for assessing hydrogen trap strength in steels and other hydrogen-sensitive alloys.