Seeing is Believing -- Understanding Environmental Degradation and Mechanical Response Using Advanced Characterization Techniques: An SMD Symposium in Honor of Ian M. Robertson: In-situ and Multi-modal Characterization of Environmental Degradation (Contributed)
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, University of Tennessee Knoxville; 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 University; Blythe Clark, Sandia National Laboratories; Shuai Wang, Southern University of Science and Technology
Thursday 8:30 AM
March 3, 2022
Room: 207C
Location: Anaheim Convention Center
8:30 AM
An Experimental-numerical Approach to Investigate Hydrogen Effects on Dislocations: Haoxue Yan1; Qingjie Li1; Jinwoo Kim1; Ju Li1; C. Cem Tasan1; 1Massachusetts Institute of Technology
The interactions between hydrogen (H) and crystallographic defects are the key to understanding hydrogen embrittlement mechanisms, including H-enhanced localized plasticity (HELP). However, unraveling such interactions on their inherent spatial and temporal scales can be challenging, due to the complex relationship between H, microstructure, and the mechanical response. To tackle this challenge, we design in situ experiments that combine electron channeling contrast imaging (ECCI), electron backscattered diffraction (EBSD) and desorption spectroscopy, to investigate H-defect interactions under no external stresses. We show that the inhomogeneous H distribution within microstructures can cause dislocation rearrangements, and discuss the effects of materials properties (i.e. yield stress and stacking fault energy) on the observed H-dislocation interactions. Moreover, by hybrid Molecular Dynamics (MD) and Grand Canonical Monte Carlo (GCMC) simulations, we provide atomistic insights into the effects of chemical composition and pre-existing dislocation structures on H-defect interactions.
8:50 AM
In Situ Investigation of the Role of Slip in Crack Initiation in Hydrogen Embrittled Alloy 725: Mengying Liu1; Lai Jiang2; Michael Demkowicz2; 1Washington and Lee University; 2Texas A&M University
The factors responsible for hydrogen embrittlement (HE) of metals remain imperfectly understood, with prevailing theories emphasizing H-induced decohesion or H-enhanced plasticity. We use in situ tensile testing to clarify the role of slip in the initiation of intergranular cracks in alloy 725. We design specialized tensile specimens, introduce hydrogen, perform in situ tensile tests in a scanning electron microscope, and track surface plastic deformation using digital image correlation. Localized slip occurs predominantly along grain boundaries. At low H concentration, cracks initiate primarily in the vicinity of slipping boundaries, albeit not at locations of greatest slip, but rather where slip is arrested. At higher H concentration, most cracks initiate at locations with no nearby localized slip. We conclude that slip is not essential for crack initiation in HE alloy 725 and that, when it does play a role, its main effect is to generate local stress concentrations that promote decohesion.
9:10 AM
In-situ 4D-STEM Imaging of Mechanical Deformation in Medium Entropy Alloy (MEA) and Bulk Metallic Glass (BMG): Yang Yang1; Sheng Yin2; Qin Yu2; Ruopeng Zhang2; Mark Asta2; Robert Ritchie2; Andrew Minor2; 1The Pennsylvania State University; 2Lawrence Berkeley National Laboratory
Traditional in-situ TEM experiments record structural information in either real space or diffraction space, but not both, limiting a comprehensive understanding of the nanostructural evolutions. Recently, the combination of four-dimensional scanning transmission electron microscopy (4D-STEM) technique with high-speed electron detectors brought hope to overcome this challenge, enabling in-situ imaging of sub-nanometer resolved mapping of strain, short-range-orders (SROs), and other structural characteristics during mechanical deformation. Here we report the in-situ energy-filtered 4D-STEM studies of the mechanical deformation in CrCoNi medium entropy alloy (MEA) and CuZr bulk metallic glass (BMG). In this presentation, we will show the detailed interactions between the SROs, localized strain, and mechanical loading. The experimental observation is further verified by molecular dynamics (MD) simulations. Our findings demonstrated that the in-situ 4D-STEM technique can provide significant new insights into the deformation mechanisms in metals.
9:30 AM
In Situ TEM Studies on the Radiation Response of Cu with Nanovoids: Cuncai Fan1; Rayaprolu Goutham Sreekar Annadanam1; Zhongxia Shang1; Meimei Li2; Anter El-Azab1; Xinghang Zhang1; 1Purdue University; 2Argonne National Laboratory
Understanding the void evolution in irradiation environment is of great interest and significance, as irradiation-induced voids typically lead to pronounced volumetric swelling and degradation of mechanical properties. In situ studies on the irradiation response of nanovoids at elevated temperature remain limited. In this work, we performed systematic in situ Kr ion irradiations on Cu with nanovoids in a transmission electron microscope up to 350 ℃. The in situ studies revealed intriguing void spheroidization, shrinkage and migration. Furthermore, the morphology evolution and migration of nanovoids showed a strong dependence on irradiation temperature and initial void size. Post-irradiation analyses identified defect clusters in the form of stacking fault tetrahedrons (SFTs), and the remaining large faceted nanovoids. The underlying mechanisms of irradiation-induced void spheroidization and shrinkage were discussed based on phase-field modeling.
9:50 AM
Revealing Hidden Defects via Stored Energy Measurements of Radiation Damage: Charles Hirst1; Fredric Granberg2; Penghui Cao3; Scott Middlemas4; R. Kemp1; Ju Li1; Kai Nordlund2; Michael Short1; 1Massachusetts Institute of Technology; 2University of Helsinki; 3University of California, Irvine; 4Idaho National Laboratory
Seeing might be believing, provided that a characterization technique can resolve the defects of interest. For radiation damage the smallest and most numerous defects are below the resolution limit of transmission electron microscopy (TEM). Instead of spatial characterization, we propose to detect defects through their excess energy. Differential scanning calorimetry (DSC) measurements of neutron-irradiated Ti reveal two energetically-distinct processes during stage V annealing. Molecular dynamics (MD) simulations reveal the defects responsible, and show that the point defect-induced glide of dislocation loops contributes significantly to recovery. In-situ TEM heating studies will be conducted to validate this mechanism. In comparison to prior literature, our experiments measure defect densities that are over 4 times greater than those determined using TEM. Accurately characterizing these ‘hidden’ defects is crucial to understanding damage and annealing mechanisms at higher length scales, and to quantifying the stability of materials to radiation damage.