Mechanical Response of Materials Investigated through Novel In-situ Experiments and Modeling: Session IV
Sponsored by: TMS Structural Materials Division, TMS Functional Materials Division, TMS: Advanced Characterization, Testing, and Simulation Committee, TMS: Thin Films and Interfaces Committee
Program Organizers: Saurabh Puri, VulcanForms Inc; Amit Pandey, Lockheed Martin Space; Dhriti Bhattacharyya, Australian Nuclear Science and Technology Organization; Dongchan Jang, Korea Advanced Institute of Science and Technology; Shailendra Joshi, University of Houston; Minh-Son Pham, Imperial College London; Jagannathan Rajagopalan, Arizona State University; Robert Wheeler, Microtesting Solutions LLC; Josh Kacher, Georgia Institute of Technology
Wednesday 2:00 PM
March 22, 2023
Room: Aqua 310B
Location: Hilton
Session Chair: Jagannathan Rajagopalan, Arizona State University
2:00 PM Invited
Precision Strain Measurement During Additive Manufacturing: Mitra Taheri1; 1Johns Hopkins University
Additive manufacturing generates extreme gradients of temperature, resulting in complex residual stress evolution. The interplay of chemistry, stress, and temperature is often overlooked in post-mortem characterization. This talk discusses the combination of machine learning and in situ microscopy approaches to a deeper understanding of residual stress evolution in additive manufacturing processes. We reveal dislocation level dependencies on strain and chemistry, and a path toward tunable microstructures through this newfound understanding.
2:30 PM Invited
In-situ TEM Observations of Dislocation and Twinning Activities of Mg via Nanoindentation: Kelvin Xie1; Lai Yi-Cheng1; Digvijay Yadav1; 1Texas A&M University
Dislocations and deformation twinning are two important deformation mechanisms of Mg. In this work, we performed in situ nanoindentation experiment on a Mg sample. 500 nm thin windows were created using the focused-ion beam technique in the sample. This thickness allows for electron transparency and avoids excessive foil bending during indentation. The indentation was performed using the PI-95 in situ picoindenter equipped with a cube-corner tip. During loading, dislocations were first activated and a well-defined plastic zone was observed. At a later stage, extension twinning was activated. It was interesting to note that both dislocation and twinning retracted during unloading, highlighting the effect of elastic stress on the dislocation and twinning behavior.
3:00 PM
Movement of Charged Dislocations in an Inorganic Compound under an Electric Field: Yu Zou1; 1University of Toronto
Dislocations are linear defects in crystalline solids, and their motion dominates many mechanical, thermal, optical and electrical properties of crystalline materials. For decades, the dislocation motion has been associated with mechanical loading or stresses, while driving dislocation motion by a non-mechanical field alone is rarely expected and has never been directly observed. Here we show an electric field drives the movement of dislocations, in the absence of mechanical loading, in a inorganic compound using in situ transmission electron microscope (TEM). Atomic-resolution imaging of the dislocation cores reveals their nonstoichiometric and charged nature. Using the density functional theory (DFT) calculations, we demonstrate that glide potentials of various partial dislocations. Our results provide pave the way for fabrication and processing of brittle crystals, such as a wide range of semiconductors, novel small-scale devices.
3:20 PM Invited
Understanding the Unique Thermal and Mechanical Properties of Nanotwinned Ni-Mo-W Alloys: Mo-Rigen He1; Gianna Valentino2; Arunima Banerjee1; Jessica Krogstad3; Kevin Hemker1; 1Johns Hopkins University; 2Johns Hopkins University Applied Physics Laboratory; 3University of Illinois Urbana-Champaign
Sputter-deposited Ni-Mo-W thin films are recently developed and shown to possess a unique suite of properties, including abnormally low thermal expansion, superior microstructural stability, and ultrahigh mechanical strength, altogether making them a promising candidate material for high-temperature microelectromechanical systems. However, the fundamental mechanisms underpinning these outstanding performances remain to be elucidated. These materials are composed of textured grains densely packed with ultrafine (< 5 nm) nanotwins, which put forth a strong demand for in situ testing and characterization at very small length scales. In this study, Ni-Mo-W alloys with varied Ni/(Mo+W) and Mo/W ratios are tested with in situ heating and pillar compression inside TEM. Based on strain measurements and crystal orientation mapping that are performed in situ and with sub-nm resolution, we try to clarify the factors (e.g., alloy composition, twin spacing, interfacial defects) that modulate elastic/plastic strain fields and control microstructural evolution in these unique family of materials.
3:50 PM Break
4:10 PM
Wear of UNCD Studied by In-situ TEM Tribometry: Rodrigo Bernal1; 1University of Texas at Dallas
Nanoscale friction and wear are extremely complex processes. As a result of this complexity many questions remain in the field. In-situ experiments are uniquely capable to answer these questions by allowing visualization of processes that are generally obscured and can only be studied by simulations. In this talk, we will discuss the visualization and quantification of wear of ultrananocrystalline diamond (UNCD) nanoscale asperities in sliding contact using in-situ transmission electron microscope (TEM) sliding experiments. Two sharp tips made of UNCD are brought into contact, enabled by a indenter TEM holder. By comparing high-resolution TEM images obtained before and after a series of sliding intervals, we quantify the evolution of wear and visualize the morphological and crystal-structure changes as wear progresses.
4:30 PM
Nanoindentation Pop-in Analysis of Oxidized Ni-based Superalloys: Malo Jullien1; Damien Texier1; Marc Legros2; 1Institut Clément Ader; 2CEMES
Ni-based superalloys are design for high temperature applications under oxidizing environment. Despite their chromina-forming abilities, they still develop internal oxidation at high and intermediate temperature. Both internal and external oxidation affect mechanical properties and make the material prone to crack initiation. Mechanical properties were probed in the oxidation affected volume thanks to large nanoindentation maps and local in situ nanoindentation experiments. Nanoindentation maps were correlated to EDX and EBSD analyses to indentify the chemical-mechanical dependence of oxidized versus virgin specimens. Oxidized grain boundaries exhibited higher hardness than non-oxidized ones and grains gore. Also the reduced modulus was found sensitive to the crystallographic orientation. Pop-in were identify on the load - indentation depth curves and related to slip activity using AFM and TEM observations.
4:50 PM
High Pressure and In-Situ TEM Deformation of Nanoscale Metallic Interfaces and Precipitates: Wendy Gu1; Abhinav Parakh1; Mehrdad Kiani2; 1Stanford University; 2Yale University
Interfaces, precipitates, and defects govern the properties of nanostructured metals and lightweight alloys. High pressure techniques are used to understand deformation during shock, impact, and ballistic loading, which include pressures of tens of GPa to Mbar. Diamond anvil cells (DAC) are used to compress lightweight alloys under quasi-hydrostatic and non-hydrostatic stress. X-ray diffraction is used to monitor structural changes in-situ, and post-compression TEM is used to directly image these changes. We find that non-hydrostatic pressure leads to a significant increase in defect density, elevated strength and the nucleation and growth of precipitates in precipitate hardened Al7075. Hydrostatic pressure leads to extensive detwinning in nanotwinned alloys with aligned twins. In-situ TEM experiments are performed on individual grain boundaries within Au bicrystals. We find that failure in these bicrystals does not seem to depend on misorientation angle or grain boundary energy, but is sensitive to surface imperfections and dislocation activity.
5:10 PM
Toughening Mechanism in Cu-Graphene Nanolayered Composite: Seung Min Han1; 1Korea Advanced Institute of Science and Technology
The role of graphene interfaces in strengthening and toughening of the Cu-graphene nanocomposite was studied using in situ transmission electron microscopy (TEM) deformation and molecular dynamics (MD) simulations. In situ TEM tests revealed that the dislocation plasticity is strongly confined within single Cu grains by the graphene interfaces and grain boundaries. The weak Cu-graphene interfacial bonding induces stress decoupling, which results in independent plastic deformation of each Cu layer. MD simulations confirmed that the localized deformation made by such constrained dislocation plasticity results in the nucleation and growth of voids at the graphene interface, which acts as a precursor for crack nucleation. The graphene interfaces also effectively block crack propagation promoted by easy delamination of Cu layers dissipating the elastic strain energy.