Phase Stability in Extreme Environments: Hydrogen in Extreme Environments
Sponsored by: TMS Structural Materials Division, TMS Materials Processing and Manufacturing Division, TMS: Corrosion and Environmental Effects Committee, TMS: Nuclear Materials Committee, TMS: Phase Transformations Committee
Program Organizers: Andrew Hoffman, Catalyst Science Solutions; Kinga Unocic, Oak Ridge National Laboratory; Janelle Wharry, Purdue University; Kaila Bertsch, Lawrence Livermore National Laboratory; Raul Rebak, GE Global Research

Tuesday 2:30 PM
March 21, 2023
Room: 28C
Location: SDCC

Session Chair: Caitlin Kohnert, Los Alamos National Laboratory

2:30 PM  Invited
Martensitic Transformations and Shear-band Interactions in Austenitic Stainless Steel: Effects of Hydrogen: Douglas Medlin¹; Julian Sabisch²; James Nathaniel¹; Joshua Sugar¹; Joseph Ronevich¹; Christopher San Marchi¹; ¹Sandia National Laboratories; ²University of Oklahoma
     The formation of deformation bands in austenitic stainless steels is often linked to shear-coupled crystallographic transformations, including twinning and the formation of ε-martensite, and can be sensitive to the presence of hydrogen. The interplay between strain and atomic shuffling in these bands can also drive further processes, such as the nucleation and growth of the α'-martensite phase at deformation band intersections. Here, we discuss electron microscopic observations of such bands and their relationship to grain boundaries and dislocation cell-walls in an austenitic stainless steel (304L), with and without hydrogen charging. Diffraction contrast STEM, nano-beam diffraction, and atomic-resolution observations provide fundamental insight concerning the elementary processes governing the nanoscale evolution of these structures.Sandia National Laboratories is a multimission laboratory managed and operated by National Technology and Engineering Solutions of Sandia, LLC., a wholly owned subsidiary of Honeywell International, Inc., for the USDOE’s NNSA under contract DE-NA-0003525.

3:00 PM  Invited
Density Functional Study of Short-range Order in Cantor Alloy and Its Effect on Point-defects: Artur Tamm¹; Shinyoung Kang²; ¹University of Tartu; ²Lawrence Livermore National Laboratory
     High entropy alloys (HEA) is a class of materials which shows improved properties compared to the individual elements making up the alloy. For example, better corrosion resistance, improved radiation tolerance and hydrogen resistance has been observed. HEAs are solid solutions in single phase and are stabilised by configurational entropy due to many elements. Moreover, the major assumption is that the elements in the HEA are randomly distributed.Our density functional theory based study of Cantor alloy shows strong evidence of short-range order (SRO). This SRO affects the point-defect properties such as vacancy formation energy. HEAs response to hydrogen is important for its use in extreme environments, such as nuclear reactor, where hydrogen build-up in the material can lead to its early failure. We investigate the role of SRO on the hydrogen embrittlement resistance of the material.

3:30 PM
Phase Stability of Metal Hydrides under Combined Radiation and Thermal Environments: Caitlin Kohnert¹; Matheus Tunes¹; Yongqiang Wang¹; Matthew Chancey¹; Tyler Smith¹; Aditya Shivprasad¹; Thomas Nizolek¹; Erik Luther¹; Tarik Saleh¹; ¹Los Alamos National Laboratory
    Metal hydrides, especially zirconium hydride (ZrH_x) and yttrium hydride (YH_x), are being considered for neutron moderators in microreactors and space reactors. These materials contain a high density of hydrogen at room temperature but begin to release hydrogen at elevated temperatures depending on the partial hydrogen pressure. Hydrogen release causes ZrH_x and YH_x to undergo a phase transformation from the hydride phase (fcc or tetragonal in ZrH_x, and fcc in YH_x) back to the metal phase (hcp in both Zr and Y), resulting in hydrogen density changes and moderation changes. Pressure-temperature-composition curves accurately describe the equilibrium hydrogen release thermodynamics in both materials, but the effects of non-equilibrium irradiation conditions on hydrogen release are not understood in these hydrides. This talk will outline our work using ion irradiation to investigate hydride phase stability and hydrogen retention in ZrH_x and YH_x during irradiation up to 2 dpa at various temperatures.

3:50 PM
Revisiting the Atomic Scale Mechanisms of Stress Corrosion Cracking of Fe-based Alloys with State-of-the-Art Microscopy and Computational Modelling: Arun Devaraj¹; Dallin Barton¹; Tingkun Liu¹; sten Lambeets¹; Cheng-han Li¹; Tanvi Ajantiwalay¹; Mark Wirth¹; Daniel Perea¹; Jinhui Tao¹; matthew Olszta¹; Maria Sushko¹; ¹Pacific Northwest National Laboratory
    When stainless steel is subjected simultaneously to an applied tensile stress and a corrosive, high-temperature aqueous medium, interplay of hydrogen and oxygen interactions with the alloy microstructure are thought to lead to intergranular stress corrosion cracking (SCC). Using novel in situ experiments in atom probe tomography, atomic force microscopy, nanomechanical testing and synchrotron high-energy x-ray diffraction, complemented with ex situ transmission electron microscopy and computational simulations, we develop an atomic scale understanding of this mechanochemical coupling during SCC of Fe-Cr-Ni model alloys. The structure and composition of oxide layers, elemental partitioning including hydrogen segregation at the oxide-metal interfaces and grain boundaries, and deformation-induced defects were revealed as a function of applied deformation. These new insights are expected to provide the scientific basis for tailoring the microstructure of Fe-based alloys used in nuclear and automotive applications for enhanced resistance to stress corrosion cracking and hydrogen embrittlement.