From Stable Expansion to Catastrophic Failure Under Extreme Hydrogen Loading in Ni and Ti Atom Probe Tomography Specimens.

To better understand hydrogen (H) trapping kinetics at the nanoscale, we recently introduced an approach consisting of in situ H implantation inside an atom probe analysis chamber operated at cryogenic temperature. This method enables implantation of H2+ ions with energies up to 1 keV, allowing H to penetrate approximately 10 nm beneath the surface of an atom probe tomography (APT) specimen. Here, we investigate the expansion of APT samples following H implantation in two metallic systems: nickel (Ni) and titanium (Ti). In Ni, a significant expansion of ≈10-15% was observed by comparing transmission electron microscopy images acquired before and after implantation. In Ti, expansion could not be directly imaged due to specimen degradation caused by room-temperature transfer; however, APT analyses revealed a substantial shift in evaporation voltage (10-40%), consistent with pronounced Ti tip volume expansion.