Environmentally Assisted Cracking: Theory and Practice : Investigating the Role of Hydrogen
Sponsored by: TMS Corrosion and Environmental Effects Committee
Program Organizers: Jenifer Locke, Ohio State University; Wenjun Cai, Virginia Polytechnic Institute and State University; Bai Cui, University of Nebraska Lincoln; Srujan Rokkam, Advanced Cooling Technologies, Inc.; Kaila Bertsch, University of Wisconsin-Madison
Monday 2:00 PM
November 2, 2020
Room: Virtual Meeting Room 30
Location: MS&T Virtual
Session Chair: Jenifer Locke, The Ohio State University; Srujan Rokkam, Advanced Cooling Technologies, (ACT) Inc.
2:00 PM Invited
Assessing the Influence of Hydrogen on The Deformation Behavior of a Precipitation-hardened Nickel-based Alloy: Zachary Harris1; Jishnu Bhattacharyya1; Joseph Ronevich2; Sean Agnew1; James Burns1; 1University of Virginia; 2Sandia National Laboratories
This study examines the effect of hydrogen (H) on the deformation behavior of Monel K-500 in various isothermal heat treatment conditions via uniaxial mechanical testing and transmission electron microscopy (TEM). In particular, H was found to modify work hardening metrics related to the dislocation storage and recovery rates. Specifically, the H-charged peak-aged specimen exhibited a significant increase in initial hardening (dislocation storage) rate relative to the H-charged under-aged specimen. Moreover, H was found to tangibly increase dislocation recovery rates for all heat treatment conditions, with the exception of the over-aged alloy. TEM of the non-charged and H-charged peak-aged specimens revealed the onset of widespread dislocation looping in the H-charged sample, while only planar slip bands were observed in the non-charged condition. Possible mechanisms to explain the observed effects of H are proposed and the applicability of these mechanistic insights to single-phase model alloys are then discussed.
2:40 PM
Atomistic Simulations of the Transport and Trapping of Hydrogen in Zirconium: Richard Smith1; Natalia Tymiak-Carlson1; Mikael Christensen2; Erich Wimmer3; 1Naval Nuclear Lab - Bettis; 2Materials Design, Inc. ; 3Materials Design, Inc.
A new set of embedded atom method interatomic potentials has been developed for the Zr-H system using an extensive suite of density functional theory calculations. The functions enable large scale simulation of both hydrogen in solution and many aspects of the important phases of hydride. They are being used to investigate the behavior of hydrogen in and around various microstructural features such as vacancies, grain boundaries and irradiation-induced <a> and <c>-type loops to better understand their influence on transport and the heterogeneous nucleation of hydrides, with the goal of improving the fidelity of continuum level calculations. Dynamic simulations give insights unavailable to static and Monte Carlo calculations due to the important influence of a ballistic transport mechanism.
3:00 PM
Hydrostatic Instability as the Underlying Mechanism of Hydrogen Embrittlement
: Michael McGuire; 1
Fundamental progress on understanding hydrogen embrittlement has been hindered by controversy over the mechanism. In this study the seemingly overlooked effect of a large hydrogen-induced lattice expansion in the densely dislocation-populated fracture process zone is predicted from first principles and confirmed experimentally. The stress relaxation caused by the hydrogen-induced expansion adjacent to the critical point is shown to be sufficient to cause a hydrostatic instability at the critical point of maximum hydrostatic stress, leading to stepwise brittle failure as the Treska failure criterion is exceeded. The mechanistic model is then tested against numerous known characteristics of hydrogen embrittlement.
3:20 PM
The Relationship between Post-build Stress-relief Heat Treatment and the Hydrogen Embrittlement Susceptibility of Additively Manufactured IN625: Mark Stoudt1; Richard Ricker1; Maureen Williams1; Fan Zhang1; 1National Institute of Standards and Technology
The combination of strength, corrosion resistance, and excellent weldability makes IN625 an attractive alloy for additive manufacturing (AM) applications, but the build process generates large compositional and residual stress gradients. Appropriate post-build heat treatments are necessary to relieve stress and produce uniform microstructures and properties; however, stress-relief also promotes the growth of carbides and intermetallic phases. Large precipitates alter the local electrochemical conditions, while the modulus mismatch with the surrounding matrix can reduce the crack propagation resistance. The question is whether these secondary phases increase the susceptibility of IN625 to hydrogen embrittlement. Slow strain rate tensile tests were performed in an acidified chloride solution using wrought and AM samples, with and without heat treatment, and under free corrosion and potentiostatic conditions that controlled the hydrogen fugacity. The experimental protocol, and the results from microstructural and fractographic analyses of the AM materials will be compared to the wrought IN625 and discussed.