Insights from quasi-in situ cryogenic-transfer atom probe tomography for analyzing hydrogen diffusion in metallic alloys

Understanding hydrogen embrittlement mechanisms requires insights into nanoscale hydrogen isotope segregation in materials. Cryogenic-transfer atom probe tomography (APT) can provide this insight, if the sample exposure is precisely controlled. Therefore, we quantified the nanoscale changes of in austenitic FeCrNi alloy during ultrahigh vacuum transfer using a LEAP 6000 XR APT system with UV laser-assisted and voltage-pulsed modes. We introduced a quasi-in situ method to study deuterium out-diffusion kinetics from electrochemically charged FeCrNi needles, which involved analyzing a deuterium-charged sample using APT, pausing for controlled thermal treatments at room temperature and 150°C, followed by reanalysis. Comparison of experimental results with a heat transfer–hydrogen diffusion model showed that slow deuterium out-diffusion was due to an oxide layer acting as a permeation barrier. These findings highlight the importance of managing sample exposure during cryogenic-transfer APT and demonstrate this quasi-in situ method’s potential for studying hydrogen isotope diffusion in metallic alloys.