Mechanical Behavior at the Nanoscale VI: On-Demand Oral Presentations
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Computational Materials Science and Engineering Committee, TMS: Mechanical Behavior of Materials Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Matthew Daly, University of Illinois-Chicago; Douglas Stauffer, Bruker Nano Surfaces & Metrology; Wei Gao, University of Texas at San Antonio; Changhong Cao, McGill University; Mohsen Asle Zaeem, Colorado School of Mines

Monday 8:00 AM
March 14, 2022
Room: Nanostructured Materials
Location: On-Demand Room

In Situ Nanomechanics of Deformation Twinning: Ting Zhu1; Yin Zhang1; 1Georgia Institute of Technology
    In this talk, I will present our recent studies that integrate in situ electron microscopy mechanical testing and atomistic modeling to investigate the deformation twinning mechanisms in FCC, BCC and HCP crystals. For example, we have unraveled a previously unknown mechanism of dual phase transformations from FCC to HCP and back to FCC with nanotwins in a nanostructured medium-entropy alloy of CrCoNi. We have observed the occurrence of anti-twinning in BCC W previously thought impossible. In addition, our atomistic simulations have revealed a dislocation-mediated mechanism of twin nucleation and growth in BCC crystals, as supported by in situ transmission electron microscopy observations. Finally, I will present a study of surprisingly large twinning shear of 120% in HCP crystals. The ability to resolve the atomic-scale twinning processes, through coupled modeling and in situ experiment, enables a deep understanding of how deformation twinning affects the plastic behavior of crystalline materials.

Precipitate Looping and Shearing at the Nanoscale: William Curtin1; Yi Hu1; Daniel Marchand1; 1Epfl Sti Igm Lammm
    Many traditional alloys are strengthened by the controlled formation of coherent in-situ nanoscale precipitates. With nanoscale size and spacing, atomistic resolution can be important but is not computationally feasible in realistic microstructures. Here, we use new machine learning interatomic potentials for Al-Mg-Si, Al-Cu, and Al-Cu-Mg, atomistically-calibrated discrete dislocation dynamics (DDD), and theory to holistically connect macroscopic yield strength to the nanoscale cutting and/or looping of precipitates. We demonstrate previously neglected differences in behavior due to precipitate orientation, which affects dislocation configurations and coherency stresses inside and outside the precipitates. We demonstrate quantitative and qualitative agreement between atomistics, DDD, and theory. We then make quantitative connections to experimentally-measured yield strengths in Al-Mg-Si Al-6xxx alloys.

Analyzing Lamellar Level Correlations between Mechanical Behavior and Composition in Mouse Bone: Shraddha Vachhani1; Surya Kalidindi2; Siddhartha Pathak1; 1Iowa State University; 2Georgia Institute of Technology
    Lamellar level correlations between the local composition and local mechanical properties in the femur of two inbred strains of mice (A/J and C57BL/6J (B6)) were studied in order to gain insights into how their extracellular matrix is mineralized. The local elastic moduli and indentation yield strengths were determined using spherical nanoindentation stress-strain analysis, while Raman spectroscopy was used to determine the local composition around the indents. Our results show a significant difference in the mineral-to-matrix ratio of the two mice strains, with the A/J mice showing an overall higher mineral-to-matrix ratio and lower carbonate substitution in the mineral. Additionally, local mineral-to-matrix ratio was found to be a good indicator of the local mechanical properties. While compositional differences are prominent in the newer bone and become less significant as the bone matured, no significant differences were observed for the correlations between mechanical behavior and composition across the two strains.

Mechanistic-design of Multilayered Metal-metal and Metal-ceramic Nanocomposites for Tunable Strength and Toughness: Siddhartha (Sid) Pathak1; 1Iowa State University
    We explore the synthesis of multilayered composites where one constituent phase has a low ductility, with a final goal of enhancing the system’s strength and toughness. We synthesized multiple multilayered systems using PVD: metal-ceramic (Cu-TiN, Al-TiN, where the ceramic is the brittle phase), metal-MAX (Nb–Ti2AlC, Ti-Ti3AlC2, where the interfaces between the layers are in direct competition with the internal interfaces within the MAX layers) and a unique bcc Mg-Nb system (where the hcp-to-bcc pseudomorphic transformation leads to enhanced ductility in Mg), with a lamellar thickness reduced to the nanoscale. We utilize a combination of nanoindentation, micro-compression, micro-tensile, and fracture toughness testing of 3-point bend micro-beams, under extremes of temperature (cryo-to-1000C) and strain rate (10^-3 to 10^3/s), and post-deformation TEM analysis to evaluate their deformation mechanisms. These results are analyzed as a function of decreasing layer thicknesses using the concepts of dislocation motion within the confined nanoscale layers.

Ligament-size Effect of Time-dependent Plasticity in Nanoporous Gold under Controlled Surface Coated Layer: Hansol Jeon1; Eunji Song1; Ju-Young Kim1; 1Unist
    The research on the time-dependent deformation as called “creep” for nanoporous gold (np-Au) is lacking while there have many studies related with time-independent properties like as tension, compression, and nanoindentation. In this study, we investigated spherical nanoindentation creep tests for np-Au with four ligament sizes in addition to surface coating of thin alumina layer. By preparing the np-Au samples without grain boundaries and cracks, we could focus on the creep properties only. We find the ligament-size dependent creep behavior, increase of total creep strain and creep strain rate with increasing ligament size, in the range of 103 nm to 986 nm. After surface coating, creep behavior increased for the ligament sizes ranging from 103 nm to 986 nm, while it decreased for ligament size of 30 nm. We discuss ligament-size dependent creep behavior and effect of surface coating with dominant creep mechanism and dislocation mechanism.

Molecular Dynamics Simulations on Nanosuspension Droplet Impact: Baiou Shi1; Siddharth Ravi1; 1Pennsylvania State University Erie
    The behavior of nano-fluids, or fluid suspensions containing nanoparticles in the realm of capillary fluid flow, has garnered tremendous attention recently for applications spanning from household and personal care products to advanced targeted drug therapy and materials fabrication. One concern is how to control the ordering of nano-particle arrays and to fabricate those functional devices. Nano-suspension provides us a path to synthesize and disperse nanoparticles in fluids, however, the fundamental mechanisms about interfaces and wetting kinetics are still unknown when a nanosuspension drop spreads on a solid surface. Herein, results from molecular dynamics simulations will be presented to explore the nanosuspension metal droplet impact process. Furthermore, results presented illustrate how the role of impact angle and velocity affect the spreading kinetics and how this connects to dynamic droplet morphology and associated particle positioning on surfaces.

Atomistic Mechanism of Stress Modulated Phase Transition in Monolayer MoTe2: Wei Gao1; 1University of Texas at San Antonio
    Monolayer MoTe2, one of the 2D transition metal dichalcogenide (TMD) materials, exhibits two stable structural phases: semiconducting 2H phase and metallic 1T'phase. The dynamic control of the transition between these two phases on a single atomically thin sheet holds promise for a variety of revolutionary device applications. Particularity, stress could be utilized to dynamically modulate such phase transition. To date, the atomistic and kinetic mechanism of the phase transition under stress is not clear. In this presentation, the finite deformation nudged elastic band method and density functional theory are applied to determine the phase transition barriers and pathways of monolayer MoTe2 as a function of applied stress. It is found that the stress can greatly influence the thermodynamics and kinetics of the phase nucleation and propagation. The results shed light on the phase engineering of 2D TMD materials with stress at the atomic level.

Theoretical Development of Continuum Dislocation Dynamics with Reactions: Preliminary Results: Kyle Starkey1; Anter El-Azab1; Thomas Hochrainer2; 1Purdue University; 2Graz University of Technology
    We present a new extension of the classical continuum dislocation dynamics which includes dislocation reactions in a general way. In the Discrete Dislocation Dynamics community, it has been known that modeling dislocation reactions are critical in obtaining the correct response of the material. However, the introduction of these types of reactions in continuum models are not as straightforward. In this talk, we introduce a geometric framework for incorporating these types of reactions. This theory involves defining density measures of dislocation junction nodes which give more information to continuum models on the dislocation reaction network, which we hope to provide us with enough information to model short-range interactions. We develop a set of mean-field transport relations for the new junction point densities and modified mean-field transport relations for dislocation vector densities. We also provide a general measure for when dislocations react which fits nicely into the proposed framework.

Development of Neural Network Potential for MD Simulation and Evaluation of Mechanical Property: Takeru Miyagawa1; Akio Yonezu1; Kazuki Mori2; Nobuhiko Kato2; 1Chuo University; 2ITOCHU Techno-Solutions Corporation (CTC)
     Titanium nitride (TiN) has been used in various applications because of its excellent wear and corrosion resistance. TiN has a rock-salt type crystal structure, which has been studied extensively, but recently the existence of non-rock-salt type phases has been reported from first-principles calculations. However, the mechanical properties of these new phases have not been studied, and it is impossible to estimate those properties from first-principles calculations because of the scale problem.In this study, we measured the mechanical properties of these new phases using the molecular dynamics (MD) simulation, which can handle larger scale models than first-principles calculations. Since the conventional many-body interatomic potentials for rock-salt TiN are not applicable to these new phases, in this study, the interatomic potentials applicable to the MD simulation were constructed using machine learning, and the mechanical properties of the new phases of TiN were measured.