Understanding the Atomic Scale Mechanisms of Oxidation and Hydrogen Embrittlement of Nuclear Structural Materials using In Situ and Cryogenic Transfer Atom Probe Tomography

When nuclear structural materials, specifically stainless steel is subjected simultaneously to applied tensile stress and a corrosive, high-temperature water, interplay of hydrogen and oxygen interactions with the alloy microstructure are thought to lead to intergranular stress corrosion cracking (SCC). Despite decades of research on SCC mechanisms of stainless steel, crucial knowledge gaps remain about the atomic scale mechanisms responsible for intergranular oxidation and hydrogen embrittlement. To overcome these knowledge gaps, we used the novel in situ atom probe tomography (APT) experiments and cryogenic transfer workflow of steel samples after electrochemical hydrogen charging. These APT experiments were complemented by insights from atomic force microscopy, nanomechanical testing, synchrotron high-energy x-ray diffraction, ex-situ transmission electron microscopy, and computational simulations. Through this multimodal approach, we developed an atomic scale understanding of the mechanochemical coupling during SCC of Fe-Cr-Ni model alloys. This effort leveraged the Ferrovac Ultrahigh vacuum cryogenic transfer module, environmental transfer hub, and cryogenically cooled sample transfer carousal and the cryogenic transfer workflow developed in PNNL for a CAMECA LEAP 4000 XHR and a CAMECA LEAP 6000 XR. This talk will highlight the new scientific understanding of oxidation and hydrogen embrittlement mechanisms enabled by these unique experimental capabilities and expertise in PNNL.