Environmentally Assisted Cracking: Theory and Practice: Hydrogen Embrittlement I
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Bai Cui, University of Nebraska Lincoln; Raul Rebak, GE Global Research; Srujan Rokkam, Advanced Cooling Technologies, Inc.; Jenifer Locke, Ohio State University
Tuesday 2:00 PM
February 25, 2020
Room: Theater A-10
Location: San Diego Convention Ctr
Session Chair: Reiner Kirchheim, Georg-August-Universität Göttingen
2:00 PM Invited
Accelerating Diffusion, Plasticity, Grain Growth and Crack Propagation by Hydrogen and Carbon: Reiner Kirchheim1; 1University of Goettingen
Within the defactant concept the formation energy of crystalline discontinuities of the first kind like vacancies, dislocations, grain boundaries and surfaces is decreased. Thus substitutional diffusion by the vacancy mechanism is accelerated. Motion of discontinuities with higher dimensions is not cooperative but occurs by generation of discontinuities of the second kind like kink pairs on dislocations or disclinations (facets) on grain boundaries. Then the motion of discontinuities of the first kind may be controlled by the generation rate and mobility of discontinuities of the second kind. Solute segregation reduces motion by the well-known solute drag. The defactant concept predicts a reduced formation energy for discontinuities of the second kind. Therefore, the generation of these discontinuities becomes easier being finally responsible for the accelerated plasticity, grain growth and crack propagation. Deacceleration occurs by solute drag controlling the motion. Experimental results are presented supporting this general thermodynamic background of solute/defect-interaction
2:40 PM
Effects of the Microstructure and Hydrogen Mobility on the Mechanical Behavior of Tempered Martensitic Steels: Livia Cupertino-Malheiros1; Abdelali Oudriss1; Daniella Guedes2; Stéphane Cohendoz1; Florent Decultieux2; Michel Piette2; Florian Thébault2; Jamaa Bouhattate1; Juan Creus1; Xavier Feaugas1; 1Université de La Rochelle - Lasie; 2Vallourec Research Center France
The present study aims to evaluate the influence of hydrogen on the mechanical behavior and susceptibility to hydrogen embrittlement of martensitic steels. For this objective, tensile tests with notched specimens were performed for hydrogen pre-charged and under hydrogen flux specimens, the latter was conducted in a permeation cell assembled directly on a tensile machine. Analyses of the fracture surfaces revealed that trapped hydrogen favors ductile fracture, whereas mobile hydrogen conduces to quasi-cleavage. EBSD maps showed that the quasi-cleavage fracture propagated mainly at the {101} plans. A local approach of the fracture using FEM calculations provided the distributions of hydrostatic stress, equivalent plastic strain, hydrogen concentration, and flux. This approach demonstrates that hydrogen reduced the critical stress for crack nucleation and enhanced the contribution of plasticity to the fracture process. These results are discussed in relation to the hydrogen embrittlement mechanisms, and more particularly in terms of hydrogen/plasticity interactions.
3:00 PM
Influence of Hydrogen on Mechanical Properties of Pure Titanium Alloys Under Cathodic Polarization in Artificial Seawater: A Local Approach to Fracture: Alexandre Poloni1; Abdelali Oudriss1; Juan Creus1; Egle Conforto1; Stéphane Cohendoz2; Jamaa Bouhattate1; Simon Frappart3; Aude Mathis3; Thierry Millot3; Feaugas Xavier1; 1University of La Rochelle - Lasie; 2University of La Rochelle, Lasie; 3Naval Group
Different kinetics of hydrogen absorption in T40 (grade 2) and TA6V ELI (grade 23) under cathodic polarization in artificial seawater have been highlighted and correlated with the phases expansion and the formation of γ and δ-hydrides. These different steps are time dependant processes which need to be taken into account to improve our knowledge of hydrogen embrittlement in titanium alloys. Mechanical tensile tests have been performed on smooth and several notched samples with and without hydrogen pre-charging. The fracture mode evolution has been studied and the impact of hydrides has been discussed using a local approach to fracture. FEM calculation offers the opportunity to associate the local hydrostatic stress σm and equivalent plastic strain εpeq leading to the fracture and to illustrate an evolution of these conditions with the hydrogen content and hydrides formation.
3:20 PM Break
3:40 PM Cancelled
Multiscale Modeling of Hydrogen Embrittlement in Stainless Steel: Ting Zhu1; David McDowell1; 1Georgia Institute of Technology
Hydrogen embrittlement of metallic materials is widely observed, but remains a challenge for predictive computational modeling. In this talk, we will describe an ongoing effort toward the multiscale modeling of hydrogen-mediated fatigue crack growth in austenitic stainless steel. An interatomic potential of the Fe-Ni-Cr-H alloy system was developed to enable the atomistic simulations of hydrogen and dislocation interactions in stainless steel. A cyclic crystal plasticity model was formulated with guidance from the atomistic reaction pathway modeling of dislocation mobility. Our crystal plasticity finite element simulations revealed the coupled hydrogen diffusion and plastic deformation at the crack tip. Further challenges and opportunities on predictive multiscale modeling of hydrogen embrittlement will be discussed.
4:20 PM
Two-way Coupled Microstructure-sensitive Crystal Plasticity and Hydrogen Diffusion Near a Blunted Crack-tip for FCC Metals: Tang Gu1; Gustavo Castelluccio2; Ting Zhu1; David McDowell1; 1Georgia Institute of Technology; 2Cranfield University
Microstructure-Sensitive Crystal Plasticity (MS-CP) modeling accounts for evolution of mesoscale dislocation substructures using a set of dislocation-based parameters that can be informed via experiments and computation at various lower length scales. MS-CP model parameters are affected by hydrogen (H) concentration, accounting for both H-enhanced initial yield strength and H-reduced rate of strain hardening. In this work, H-affected MS-CP model is two-way coupled with H-diffusion to explore (i) effects of plastic deformation on H-diffusion and (ii) effects of H on strength and strain hardening. Crack tip simulations are performed for FCC metals under monotonic loading conditions with and without H. Increased localization of plastic strain and dislocation density are predicted near the crack tip in the presence of H, consistent with experimental observations. In contrast, H-enhanced initial strengthening inhibits localization of crack tip plastic deformation, demonstrating the dominant role of the reduced rate of strain hardening in modeling effects of H.
4:40 PM Cancelled
Influence of Hydrogen Partitioning on Deformation and Fracture Behavior in Al-Zn-Mg Alloys: Kazuyuki Shimizu1; Hiroyuki Toda1; Kyosuke Hirayama1; Hiro Fujihara1; Kentaro Uesugi2; Akihisa Takeuchi2; 1Kyushu University; 2JASRI
Hydrogen trapped various sites degrade the mechanical properties of aluminum alloys. The removal of hydrogen in the material by using special casting processes or heat treatments can improve the mechanical properties, but it is not feasible from the viewpoint of practical application. In this study, we propose hydrogen-partitioning-control, aiming to minimize hydrogen embrittlement by controlling hydrogen partitioning behavior. To analyze hydrogen partitioning and related hydrogen embrittlement, some experimental techniques such as optical/electron microscopy, and synchrotron X-ray tomography were utilized. In-situ observation of hydrogen embrittlement behavior was also performed by means of synchrotron X-ray tomography. As the results, hydrogen-induced quasi-cleavage cracking and strain localization in Al-Zn-Mg alloys were observed. The hydrogen re-partitioning behavior was analyzed based on both hydrogen occupancy and hydrogen trap-site density in strain localized region. It has been suggested that a large amount of hydrogen accumulation at the precipitate/aluminum interface originate quasi-cleavage crack.
5:00 PM Cancelled
Hydrogen Trapping and Bubble Formation in Nanovoids in BCC Metals: A Predictive Model: Jun Song1; Jie Hou1; 1McGill University
Hydrogen-nanovoid interaction is central to understanding formation and growth of pressurized hydrogen bubbles that cause hydrogen-induced damages in structural metals. Focusing on tungsten as a representative model system for BCC metals, we examined hydrogen adsorption within nanovoids employing comprehensive first-principles calculations. We explicitly demonstrated sequential adsorption of hydrogen adatoms on Wigner-Seitz squares of nanovoids with distinct energy levels, with interaction between hydrogen adatoms dominated by pairwise power-law repulsion. A predictive model has then been established for quantitative determination of configurations and energetics of hydrogen adatoms in nanovoids. This was further combined with equation of states of hydrogen gas to accurately predict hydrogen bubble formation. Furthermore, multiscale simulations based on our predictive model were performed, yielding excellent agreement with recent thermal desorption experiments. Our work clarifies fundamental physics and provides a full-scale predictive model for hydrogen trapping and bubbling in structural metals, offering long-sought mechanistic insights for understanding hydrogen-induced damages.