Mechanical Behavior at the Nanoscale VI: LIVESTREAMED SESSION: Nanomechanics-coupled Material Physics
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

Wednesday 2:00 PM
March 2, 2022
Room: 204B
Location: Anaheim Convention Center

Session Chair: Douglas Stauffer, Bruker Nano Inc.; Katherine Jungjohann, Sandia National Laboratories

2:00 PM  Invited
Impact of Hydrogen on Dislocation Nucleation and Strength in bcc Fe-Cr Alloys: Gerhard Dehm1; Jing Rao1; Maria Jazmin Duarte1; 1MPI Eisenforschung
    Hydrogen is one of the energy carriers of the future, but its application is still hampered by hydrogen embrittlement (HE) of metals. Discriminating the different HE effects experimentally requires to probe mechanical properties of materials under hydrogen exposure also at the microstructure length scales. This lead to in-situ electrochemical charging of samples combined with nanoindentation. In this talk, we report on a new electrochemical cell design for nanoindentation avoiding unwanted corrosive attack of the surface and recent results on bcc Fe-Cr alloys. Our nanoindentation and micro-pillar compression experiments consistently show a reduction in critical resolved shear stress for dislocation nucleation, in accordance to the defactant theory. In addition, we observe that the lower stress for dislocation nucleation leads to a higher increase in dislocation density. Differences and similarities between nanoindentation and pillar compression under hydrogen charging will be discussed. The findings for Fe-Cr will be compared to other bcc metals.

2:30 PM  
Micro-mechanical Characterization of Geometric and Defect Dependent Responses in 3D Kirigami Polymer Structures: Jungkyu Lee1; Kian Bashandeh2; Andreas Polycarpou2; 1Bruker Nano Surfaces Division; 2Texas A&M University
    Through the controlled buckling of 2D precursors drawing inspiration from kirigami, 3D micro-scale structures can be fabricated through highly scalable processes. By using shape memory polymer materials, these structures can undergo large elastic strains, making them suitable for a variety of applications in wearable electronics, energy generation and storage, sensors, and more. However, to optimize mechanical performance and reliability for such devices, a variety of factors must be evaluated including the geometry of the structure, presence of defects, and the performance under cyclic loading. To explore this, we utilized highly sensitive nanoindentation-based instruments to evaluate various geometries of three-dimensional shape memory polymer (SMP) structures composed of epoxy monomers. The load-displacement response and its hysteresis were determined for several conditions, including various pre-existing flaws and room temperature versus 72 C. Finite element modeling was employed to accompany the experiment by analyzing the internal stress distribution of the structures.

2:50 PM  Invited
Nanoscale Characterization of Electrochemical-mechanical Mechanisms with Electron Microscopy: Katherine Jungjohann1; Daniel Long1; Katharine Harrison1; Laura Merrill1; Zach Milne1; Khalid Hattar1; 1Sandia National Laboratories
    In-situ scanning/transmission electron microscopy (S/TEM) and cryogenic electron microscopy are being used to explore nanoscale mechanical degradation and failure in electrochemical systems. The combination of environmental reactions with mechanical stress dictates the electrode performance, commonly used for Li-ion batteries. The mechanical effects span the battery cell from the electrode/electrolyte interfaces through the polymeric separator. This presentation will cover the use of cryogenic electron microscopy to study the nanoscale mechanical response of lithium electrodes after charge cycling under varied pressures and at different rates. In addition, we have been developing a microelectromechanical system (MEMS) platform for in-situ S/TEM observation of the electrode response to applied tension during electrochemical cycling. Progress on these two topics will be discussed, including opportunities and limitations for each beyond energy storage systems. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.

3:20 PM Break

3:40 PM  
Thermal Stability of Nanocrystalline NiYZr Alloys: Saurabh Sharma1; Kris Darling2; Vikrant Beura1; Yashaswini Karanth1; Kiran Solanki1; 1Arizona State University; 2Army Research Laboratory
    Thermal stability of nanocrystalline Ni-Y-Zr duplex alloys, wherein both grain boundary segregation (some solid solubility of Zr in Ni) and phase formation (e.g., Ni-Y and Ni-Zr precipitates) occur, was investigated. The initial materials with different compositions were synthesized using ball-milling. The microstructural changes after annealing (up to 1473K) were characterized using X-ray-line-broadening, micro-hardness, ion beam channeling contrast imaging, and transmission electron microscopy. Results demonstrated that the rate of grain growth observed in Ni-Y-Zr ternary alloy at 873K is similar to the growth rate in pure NC-Ni at 373 K. Furthermore, the maximum hardness of 753 HV was obtained for Ni-Y-Zr ternary system at 873 K, approximately 60 HV greater than Ni-Y, Ni-Zr binary alloys, and more than double as compared to pure NC-Ni. Overall, the thermal stability of ternary alloy has been enhanced due to the presence of Y and Zr.

4:00 PM  
Molecular Dynamics Modeling of Helium Nanobubble Growth in Irradiated Copper Matrix: Ali K. Shargh1; Ognjen Bosic1; Niaz Abdolrahim1; 1University of Rochester
    Irradiation of metals under high energy alpha particles is often accompanied with formation of helium nanobubbles in the matrix and leads to moderate degradation in their mechanical properties and structural integrity. While recent experiments have demonstrated that the extent of such degradation depends on thermodynamic characteristics of full-grown bubbles such as: internal pressure, little is known on atomic-scale deformation mechanisms responsible for controlling bubble pressure. Using MD simulations, we present a novel deformation mechanisms map for copper matrix containing helium nanobubbles with different morphological parameters such as: bubble diameter, inter-bubble distance, and helium to vacancy ratio (He/V). Different deformation mechanisms such as: crystallization, formation of immobile stacking-fault octahedra as well as punching out of prismatic and triangular dislocation loops will be discussed. In addition, we develop an equation of state based on Donnelly model for predicting the nanobubble pressure from its diameter as well as He/V at various temperature.

4:20 PM  
Understanding the Local Structure-property Relationships of Pb-Sn Solders in Terrestrial vs. Microgravity Environments: Manish Kumar1; Sid Pathak1; 1Iowa State University Ames
    We characterized the microstructure and resultant micro-to-nanomechanical response of solders in terrestrial vs. microgravity environments, 1g vs. ~110-5g. The In-Space Soldering Investigation (ISSI) experiments performed aboard the International Space Station (ISS) have shown that soldering in microgravity is expected to be considerably different than their ground-based counterparts due to Earth’s natural convective flow and buoyancy effects being minimized in microgravity during melting and solidification. Using Lead(Pb)-Tin(Sn) solders from the ISSI, we demonstrate how the lack of Earth’s natural convective flow and buoyancy effects during melting/solidification onboard the International Space Station affects its microstructure and performance. Our current scanning electron microscope (SEM) imaging results demonstrate a considerable amount of internal porosity (about three times that of ground-based solder) and inhomogeneous vs. homogeneous distribution of the Sn-rich and Pb-rich regions of the terrestrial vs. microgravity solders, respectively. We also observed a lower strength in the microgravity solders from nanoindentation testing.