Advanced Characterization Techniques for Quantifying and Modeling Deformation: Session I
Sponsored by: TMS Extraction and Processing Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Materials Characterization Committee
Program Organizers: Rodney McCabe, Los Alamos National Laboratory; Marko Knezevic, University of New Hampshire; Irene Beyerlein, University of California, Santa Barbara; Wolfgang Pantleon, Technical University of Denmark; C. Tasan, Massachusetts Institute of Technology; Arul Kumar Mariyappan, Los Alamos National Laboratory; Olivia Underwood Jackson, Sandia National Laboratories
Monday 8:30 AM
March 15, 2021
Room: RM 13
Location: TMS2021 Virtual
8:30 AM Invited
Mechanism of Hardening and Damage Initiation in Oxygen Embrittlement of Body-Centred-Cubic Niobium: Weizhong Han1; 1Xi'an Jiaotong University
Body-centred-cubic metallic materials, such as niobium (Nb) and other refractory metals, are prone to embrittlement due to low levels of oxygen solutes. The mechanisms responsible for the oxygen-induced rampant hardening and damage are unclear. Here we illustrate that screw dislocations moving through a random repulsive force field imposed by impurity oxygen interstitials readily form cross-kinks and emit excess vacancies in Nb. The vacancies bind strongly with oxygen and screw dislocation in a three-body fashion, rendering dislocation motion difficult and hence pronounced dislocation storage and hardening. While self-interstitials anneal out fast during plastic flow, the vacancy-oxygen complexes are stable against passing dislocations. The debris in fact amplify the random force field, facilitating the generation of even more defects in a self-reinforcing loop. This leads to unusually high strain hardening rates and fast breeding of nano-cavities that underlie damage and failure. Ref. Acta Mater-2019-168-331 and Acta Mater-2019-179-107.
9:00 AM
Evaluation Method of Ductile-to-Brittle Transition Temperature Using Nano-indentation and Molecular Dynamics Simulation: Yeonju Oh1; Won-Seok Ko2; Nojun Kwak1; Takahito Ohmura3; Heung Nam Han1; 1Seoul National University; 2University of Ulsan; 3National Institute for Materials Science
Tungsten has emerged as a promising material for use in a variety of high-temperature applications; however, the characterization of its ductile-to-brittle transition is currently limited to large scale scenarios and destructive testing. In this presentation, we propose a novel non-destructive method to evaluate the ductile-to-brittle transition temperature (DBTT) of pure tungsten at extremely small scales. The new concept is based on constructing a practical Yoffee diagram where the effective yield stress is evaluated from pop-in behavior during nano-indentation, and the brittle fracture stress is calculated on the basis of MD simulation. Experimental validation has been made by tensile test confirming the availability of the proposed method as an engineering tool to estimate the DBTT. Based on the new method, we’ve examined the DBTT variation of four tungsten specimens with different degree of deformation. Further details on microstructure dependence of DBTT in tungsten would be discussed in terms of dislocation characters.
9:20 AM
Migration kinetics of twinning disconnections in nanotwinned Cu: an in situ HRTEM deformation study: Quan Li1; Jian Song1; GuiSen Liu1; Yue Liu1; XiaoQin Zeng1; 1Shanghai Jiao Tong University
Growth or annealing twins normally form rectangular shape with abundant incoherent twin boundaries (ITBs), while deformation twins exhibit lenticular shape that composed of serrated coherent twin boundaries (SCTBs). Using in situ high-resolution TEM deformation technique, here we report the formation-mechanism differences between 1-layer or 2-layer serration/facet and {112} ITBs. The atomic resolution microscopy results of nanotwinned Cu manifested the 1-layer and 2-layer serration/facet formation on CTBs by interaction of mixed partial dislocations, via migration of twinning disconnections (TDs) along shearing direction. In comparison, periodic 3-layered TDs or ITBs structure were normally formed by annealing or growth process introduced spontaneous directionless partial dislocations.
9:40 AM
High Angular Resolution EBSD From Spherical Harmonic Transform Indexing: Gregory Sparks1; Mark Obstalecki2; Paul Shade2; Michael Uchic2; Stephen Niezgoda1; Michael Mills1; 1Ohio State University; 2Air Force Research Laboratory
High-energy diffraction microscopy provides nondestructive 3D data on the local crystalline structure and elastic strains within polycrystalline metals, and can be combined with in-situ mechanical testing to quantitatively characterize microstructure evolution during deformation. However, spatial mapping of the deformation-induced crystal reorientation at and below the scale of subgrains is limited for current HEDM methods. The present project is exploring the use of improved-resolution EBSD, intended to be combined with serial sectioning to produce 3D data reconstructions that can be correlated with HEDM data. This presentation details our efforts to quantify the precision of "spherical harmonic transform indexing," a recently introduced EBSD indexing technique. The best angular resolution found was 0.016°, which approaches the resolution reported in the literature for other high-resolution EBSD implementations. At this resolution, the noise floor for geometrically necessary dislocation density calculations was found to be approximately 7 × 1012 m-2 with a 200 nm step size.
10:00 AM
Kinking in MAX Phases Studied via a Combined Experimental/Computational Approach: Gabriel Plummer1; Garritt Tucker1; 1Colorado School of Mines
Kinking is a novel deformation mode in systems exhibiting plastic anisotropy. These include geological formations, laminated composites, and layered crystalline solids such as graphite, mica, and MAX phases. It is particularly relevant in the latter, ternary carbides and nitrides, being implicated in some of their unique properties, most notably an ability to dissipate large quantities of mechanical energy. Despite its fundamental relevance to crystal plasticity, an understanding of the mechanisms responsible for kinking has remained elusive for 70+ years. Recently, we have developed interatomic potentials for MAX phases, which now enable simulations at the length and time scales relevant to kinking. Combining these simulations with the deformation of single crystals, we show that kinking arises due to a coupling of atomic layer buckling with concomitant basal dislocation nucleation. Importantly, the latter cannot occur without the former. These results are a fundamental advance in understanding the deformation of crystalline layered solids.
10:20 AM
Studying Dislcoation Interactions in the Bulk Using Dark Field X-ray Microscopy: Henning Friis Poulsen1; 1DTU
We present first results from the hard x-ray microscope recently established at ESRF, Grenoble. Using dark-field X-ray microscopy, DFXM, we directly visualize the long-range strain fields arising from a multitude of dislocations as they move and interact over hundreds of micrometers, deep inside the bulk. Our experiments reveal the cooperative thermal motion of a dislocation boundary and its interaction with a low-angle grain boundary in aluminum. We zoom in to resolve the mechanism by which a free dislocation inserts into the boundary and contrast this with another dislocation that emits from the boundary. This new approach has the potential to directly guide and validate multiscale models of microstructure and dislocation patterning. We outline the potential and limitations of DFXM for understanding patterning and for multiscale modelling of mechanical properties. This work represent collaborative efforts involving DTU, ESRF, LLNL and Purdue.
10:40 AM
Interactions between Dislocations and a Low-angle Grain Boundary in a Single Crystalline CrCoNi Medium-entropy Alloy: Frederic Habiyaremye1; Antoine Antoine Guitton1; Florian Schafer2; Felicitas Scholz3; Mike Schneider3; Jan Frenzel3; Guillaume Laplanche3; Nabila Maloufi1; 1Université de Lorraine–CNRS–Arts et Métiers ParisTech–LEM3; 2Saarland University; 3Institut für Werkstoffe, Ruhr–Universität Bochum, Universitätsstr. 150
This work investigates interactions of deformation-induced dislocations with a low-angle grain boundary (LAGB) in a single-crystalline CrCoNi medium entropy alloy. Microstructures before and after µN-nanoindentation were examined using accurate electron channeling contrast imaging. Initially, the microstructure consists of subgrains separated by LAGBs. After nanoindentation on the (001) plane in the vicinity of a LAGB with a misorientation angle of 0.24°, deformation-induced dislocations formed pile-ups on {111} planes. These well-oriented pile-ups of dislocations were found to be blocked by the LAGB. Even though pile-ups interacted with the LAGB and that the extension of the pile-ups was constrained by the LAGB, micromechanical behaviors were similar to that observed when nanoindentation tests were performed far away from the LAGB. The LAGB is, therefore, a strong obstacle to dislocation motion and we point out areas for future research using nanoindentation in combination with advanced characterization methods to study the interaction between dislocations and LAGBs.
11:00 AM
Electron Microscopy-based Assessment of the Role of Short Range Order on Deformation Behavior of High and Medium Entropy Alloys: Daniel Foley1; James Hart1; Elaf Anber2; Robert Ritchie3; Andrew Minor3; Mark Asta3; Flynn Walsh4; Douglas Spearot5; Mitra Taheri1; 1Johns Hopkins University; 2Drexel University; 3University of California, Berkeley; 4Lawrence Berkeley National Laboratory; 5University of Florida
Despite their nominal chemical disorder, several studies have reported short range order (SRO) in high entropy alloys (HEAs) – i.e. preferential bonding, local elemental enrichment and/or clustering – such SRO may have broad implications for HEA performance. In an FCC metal or alloy the mode of deformation, such as slip or twinning, is dependent on that alloy’s stacking fault energy (SFE) and the energetic landscape encountered by dislocations. The assumed chemical disorder in HEAs is thought to lead to locally variable SFE, but it remains unclear how SRO modulates this energetic landscape. To tackle this problem, a suite of spatially resolved electron imaging, diffraction, and spectroscopy techniques is leveraged to correlate local order with deformation induced microstructural evolution in high and medium entropy alloys. The techniques presented enable the direct observation of the interplay between chemistry and microstructure, establishing local order as a key tuning knob for future HEA development.