Seeing is Believing -- Understanding Environmental Degradation and Mechanical Response Using Advanced Characterization Techniques: An SMD Symposium in Honor of Ian M. Robertson: Broader Impacts and Environmental Degradation I: Hydrogen Embrittlement
Sponsored by: TMS Extraction and Processing Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Chemistry and Physics of Materials Committee, TMS: Corrosion and Environmental Effects Committee, TMS: Mechanical Behavior of Materials Committee, TMS: Nuclear Materials Committee
Program Organizers: Kaila Bertsch, Lawrence Livermore National Laboratory; Khalid Hattar, Sandia National Laboratories; Josh Kacher, Georgia Institute of Technology; Bai Cui, University of Nebraska-Lincoln; Benjamin Eftink, Los Alamos National Laboratory; Stephen House, University of Pittsburgh; May Martin, National Institute Of Standards And Technology; Kelly Nygren, Cornell High Energy Synchrotron Source; Blythe Clark, Sandia National Laboratories; Shuai Wang, Southern University of Science and Technology

Monday 8:30 AM
February 28, 2022
Room: 207C
Location: Anaheim Convention Center

Session Chair: Kaila Bertsch, Lawrence Livermore National Laboratory; Kelly Nygren, Cornell University/CHESS; May Martin, National Institute of Standards and Technology; Shuai Wang, Souther University of Science and Technology; Bai Cui, University of Nebraska- Lincoln

8:30 AM Introductory Comments

8:40 AM  Invited
NOW ON-DEMAND ONLY - Hydrogen Embrittlement: From Experiments and Modeling to Prognosis: Petros Sofronis1; Zahra Hosseini1; Mohsen Dadfarnia2; Masanobu Kubota3; Akihide Nagao3; Brian Somerday1; Robert Ritchie4; 1University of Illinois; 2Seattle University; 3Kyushu University; 4University of California, Berkeley
    Recent experimental studies of the microstructure beneath fracture surfaces of ferritic steel, lath martensitic steel, stainless steel, and nickel specimens fractured in hydrogen suggest that the dislocation structure and hydrogen transported by mobile dislocations play important roles in the evolution of the fracture process/event. After reviewing this plasticity-mediated hydrogen-induced failure, we present a model for hydrogen/deformation interactions to quantify the effect of hydrogen on the fracture resistance of a low alloy martensitic steel through the use of a statistically-based micromechanical model for the critical local fracture event, which relates the influence of hydrogen on dislocation interactions and internal interfaces in affecting decohesion to the onset of macroscopic failure. The results demonstrate that hydrogen induced failures are complex phenomena that can be explained by a combination of HELP and decohesion and require factors such as stress, strain, and hydrogen concentration to all act in concert to bring about failure.

9:10 AM  Invited
Multi-scale Characterization of the Effects of High Altitude Environments on Crack Tip Damage Evolution during Fatigue Loading of AA7075-T651: James Burns1; Zach Harris1; Adam Thompson1; 1University of Virginia
     Aerospace aluminum alloys often operate at high altitude (typified by low temperatures and water vapor pressures (PH2O)); such environments slow the fatigue crack growth behavior. Incorporating these benefits into structural life management requires an understanding of the governing damage physics.The low temperature behavior retardation may be due to changes in dislocation structure evolution and/or on the hydrogen environment embrittlement (HEE) process. The HEE process would be influenced by temperature via a reduction in bulk PH2O, crack tip reaction kinetics producing/absorbing atomic H, H diffusion in the process zone, and/or changing the nature of the H-dislocation interactions. A novel multi-scale characterization (e.g. EBSD, FIB-TEM,ASTARS) of the damage structure in the crack wake of different samples evaluating the impact of individual variables such as driving force (ΔK), temperature and PH2O is performed with the goal of providing insights into the governing mechanisms of high altitude environment fatigue.

9:40 AM  Invited
Factors Influencing Fatigue Crack Growth Properties of Steels in Hydrogen Gas Environment: Hisao Matsunaga1; 1Kyushu University
    It is well known that hydrogen gas environment accelerates fatigue crack growth in the majority of steels. The degree of acceleration is influenced by various factors such as gas pressure, temperature, loading rate, material type, material’s strength and microstructure. These factors should adequately be taken into account in the strength design of hydrogen components, however, each factor has not been well understood with its influencing mechanism. In the presentation, some important experimental results are introduced with the results of microscopic observation of crack and fracture surface, and then the mechanisms are discussed.

10:10 AM Break

10:25 AM  Invited
NOW ON-DEMAND ONLY - Effect of Hydrogen on Creep Properties: Masanobu Kubota1; Daisuke Takazaki2; Ryosuke Komoda3; Kentrao Wada2; Toshihiro Tsuchiyama4; Mohsen Dadfarnia5; Brian Somerday6; Petros Sofronis7; 1I2CNER, Kyushu University; 2Graduate School of Kyushu University; 3Fukuoka University & I2CNER, Kyushu University; 4Kyushu University; 5Seattle University & I2CNER, Kyushu University; 6University of Illinois at Urbana-Champaign, Somerday Consulting LLC & I2CNER, Kyushu University; 7University of Illinois at Urbana-Champaign & I2CNER, Kyushu University
    It is expected that high-temperature hydrogen technologies such as solid oxide fuel cell and high-temperature water electrolysis will take important role in hydrogen society. Regarding the degradation of structural materials in high-temperature hydrogen, high-temperature hydrogen attack is most prominent manifestation. However, studies on other types of failure are quite limited. In this study, a creep test of SUS304 austenitic stainless steel was carried out in hydrogen at 873K. The creep rate at the secondary creep region in hydrogen was significantly accelerated. It resulted significant reduction in the creep life. In argon, the fracture surface changed from dimple to intergranular cracking with the increase in creep life. In hydrogen, this change was delayed. Regarding the mechanism, it was confirmed that decarburization, carbide formation and HELP were minor in this experiment. Instead, enhanced dislocation climb mediated by increased vacancy density is a plausible mechanism, although further investigation is needed.

10:55 AM  Invited
NOW ON-DEMAND ONLY - Effects of Hydrogen on Deformation Evaluated with EBSD of Single Crystal Austenitic Stainless Steel: Brian Kagay1; Coleman Alleman1; Brandon Talamini1; Chris San Marchi1; 1Sandia National Laboratories
    The effects of internal hydrogen on deformation features in 316 austenitic stainless steel were evaluated through electron backscatter diffraction (EBSD) of plastically deformed single crystal tensile specimens. Single crystal specimens oriented with three different crystallographic directions parallel to the tensile axis were used so that the deformation mechanisms occurring for specific orientations and numbers of active slip planes could be evaluated. Specimens with and without internal hydrogen were incrementally strained in tension, and the evolution of the deformed microstructure was interrogated by EBSD. Specifically, the quantity of geometrically necessary dislocations, occurrence of twinning, and crystal rotation are correlated to the initial crystal orientation and stress-strain response. The experimentally observed tensile flow properties and deformation mechanisms are correlated with crystal plasticity simulations of a digital representation of each single crystal to develop insight into the influence of hydrogen on deformation modes and to advance the crystal plasticity simulations of polycrystalline materials.

11:25 AM  Invited
The Central Role of the Chemical Potential of Hydrogen Regarding Hydrogen Ingress, Trapping, Defect Generation and Fracture: Reiner Kirchheim1; 1University of Goettingen
    Corrosion reactions determine the maximum chemical potential of hydrogen. Examples for iron, nickel and aluminum are presented. The self-diffusion coefficient of hydrogen in the metal is determined by the product of the H-diffusion in the perfect lattice times the fraction of hydrogen being diffusible. In this context, the quantities diffusible hydrogen, lattice hydrogen, thermodynamic activity of hydrogen and chemical potential of hydrogen are interchangeable in a general way. New discontinuities (fracture surfaces, voids, dislocations) are generated during hydrogen embritllement. The production rate of these discontinuities depends on the chemical potential of hydrogen within the defactant concept or the generalized Gibbs adsorption isotherm. Thus, the chemical potential of hydrogen determines both the amount of trapping and the defect generation rate. For a crack the chemical potential affects its velocity independent of the accompanying concentration enhancement in front of the crack tip or the H-coverage on the freshly generated crack surface.