Phonons, Electrons and Dislons: Exploring the Relationships Between Plastic Deformation and Heat: Session I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Shaping and Forming Committee
Program Organizers: Aashish Rohatgi, Pacific Northwest National Laboratory; Sean Agnew, University of Virginia; Thomas Bieler, Michigan State University

Monday 8:30 AM
March 15, 2021
Room: RM 42
Location: TMS2021 Virtual

Session Chair: Aashish Rohatgi, Pacific Northwest National Lab; Sean Agnew, University of Virginia; Thomas Bieler, Michigan State University


8:30 AM  
Introductory Comments: Phonons, Electrons and Dislons: Exploring the Relationships between Plastic Deformation and Heat: Aashish Rohatgi1; 1Pacific Northwest National Laboratory
    Introductory Comments

8:35 AM  Invited
Introduction to Dislons: A Quantized Description of Dislocations with Implications for Thermal and Electrical Transport: Mingda Li1; 1Massachusetts Institute of Technology
    Dislocations, as a type of crystallographic defects, contain a few fascinating features such as topological protection, long-range interaction, and the deep connections to various fields in physics such as superconductors and phase transitions. In this presentation, we introduce our theoretical effort by treating a dislocation as a quantum field, aka a "dislon", why and how a classical dislocation shall be quantized, and the qualitatively new electronic and phonon behaviors enabled through the dislocation quantization, such as phonon instabilities beyond defect scattering and novel electronic and phonon phases, supported by recent simulations and experiments. We conclude by explaining the necessity and exciting opportunities the quantum field approach may bring to elucidate the roles classical crystallographic defects may play in materials electronic and thermal properties.

8:55 AM  
Inelastic Neutron Scattering Investigation of the Phonon Spectra of Dislocated Nb Crystals: Sean Agnew1; Thomas Bieler2; Matthew Stone3; 1University of Virginia; 2Michigan State University; 3Oak Ridge National Laboratory
    Even modest dislocation densities have been shown to have a profound impact upon the phonon-dominated heat transfer of Nb near 2K. At higher temperatures, heat transfer is primarily electron-mediated, so the effect of dislocations on phonon behavior cannot be assessed using measurements of thermal transport alone. At very high dislocation densities, it has been predicted that even single-atom unit cells may exhibit an optical phonon mode. Inelastic neutron spectroscopy (INS) experiments on the Wide Angular-Range Chopper Spectrometer (ARCS) at the Spallation Neutron Source at Oak Ridge National Laboratory are used to examine the phonon spectra of highly pedigreed single crystals of Nb in the highly annealed, uniaxially deformed to moderate strain levels (30%), and heavily rolled conditions at 4K, 50K, and 300K. The results will be discussed in the context of classical observations of thermal transport and modern dislon theory.

9:15 AM  Invited
Dislocation-limited Thermal Transport in III-Nitride Materials: Lucas Lindsay1; Hongkun Li2; Riley Hanus1; Carlos Polanco1; Andreas Zeidler3; Gregor Koblmuller3; Yee Kan Koh2; 1Oak Ridge National Laboratory; 2National University of Singapore; 3Technical University of Munich
    Wide bandgap semiconductors (e.g. III-Nitrides) are of extensive technological importance, especially for high power electronics and light emitting diodes. For such applications, thermal management is a critical challenge as manipulating the electrons inevitably generates Joule’s heating of active regions in device architectures. Here I discuss recent pump-probe transport measurements and first principles calculations providing insights into the interplay of thermal resistance mechanisms limiting III-Nitride functionalities, particularly regarding the role of dislocations. We have demonstrated that phonon-dislocation scattering in GaN is weaker than suggested by previous measurements, likely due to sample and experiment size effects. Nonetheless, dislocation-limited k and k anisotropy are observed in InN and GaN films with highly oriented dislocations at high densities. These efforts suggest novel pathways for tuning k via defect engineering. L.L. acknowledges support from the U. S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division.

9:35 AM  
Role of Tantalum Concentration and Processing Temperature on High Strain Rate Phonon Behavior in Copper-tantalum Alloys: Soundarya Srinivasan1; Scott Turnage2; Billy Hornbuckle2; Chaitanya Kale1; Kris Darling2; Kiran Solanki1; 1Arizona State University; 2Army Research Laboratory
    Microstructural instability in traditional nanocrystalline metals limits the understanding of grain size effects on mechanical behavior under extreme conditions like high temperature and loading rates. In this work, interplay between Ta concentrations and processing temperature on the resulting microstructure of a powder processed fully dense Cu-Ta alloy and their tensile behavior at different strain rates are investigated, to probe the possibility to tune microstructurally dependent parameters to control the flow-stress upturn phenomenon. Consequently, the results reveal that there is a crucial length scale, i.e., grain size and cluster spacing, below which phonon drag is damped out and above which phonon drag becomes progressively active. This observation of changes in phonon drag are consistent with the observed changes in measured plasticity/ductility, which presents itself as an inversion in tension ductility. Overall, this work demonstrates a systematic way to control the phonon drag effects in metallic alloys for high rate applications.

9:55 AM  Invited
Dislocation Drag in Metals: Dependence on Velocity, Temperature, Density, and Crystal Geometry, and Its Effect on Material Response: Daniel Blaschke1; Leonid Burakovsky1; Abigail Hunter1; Darby J. Luscher1; Dean L. Preston1; 1Los Alamos National Laboratory
    The mobility of dislocations is an important factor in understanding material strength. Dislocations experience a drag due to their interaction with the crystal structure, the dominating contribution at high stress and temperature being the scattering off phonons due to phonon wind. Yet, the functional dependence of this effect on velocity and other properties has eluded a good theoretical understanding. In this talk we present recent results on dislocation drag from first principles as a function of velocity (resp. stress), temperature, density, and character. We then discuss the impact this newly derived drag coefficient has on the overall material response by presenting selected examples from single crystal plasticity simulations as well as an analytical model of stress as a function of strain rate which takes into account mobile-immobile dislocation intersections as well as dislocation drag from phonon wind.

10:15 AM  
The Effects of Heating Rate on Defect Reduction by Recrystallization in Deformed Polycrystal Niobium: E. Nicometo1; Z. Thune1; C. Edge1; T. Bieler1; 1Michigan State University
    Niobium superconducting radio frequency cavities are the central core structure of particle accelerators. When in the superconducting state, defects such as dislocations and low angle grain boundaries arising from ingot production and sheet metal processing can trap magnetic flux and dissipate energy that degrades cavity performance (and thermal conductivity). We hypothesize that a more rapid heating rate than in current use will enable recrystallization that is more effective in removing defects. Two sets of polycrystal niobium samples with different orientations with respect to the rolling direction (one each from the cavity itself and from the adjacent material trimmed before forming the cavity) were studied by analyzing local average misorientation values collected by electron backscatter diffraction analysis before and after heat treatment. By understanding how initial deformation gradients from forming influences recrystallization after heat treatment, adjustments in the process can make future cavities more consistently efficient by minimizing defects.