Mechanical Behavior at the Nanoscale VI: Deformation Mechanisms II
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

Tuesday 8:00 AM
March 1, 2022
Room: 262B
Location: Anaheim Convention Center

Session Chair: Douglas Stauffer, Bruker Nano Inc.; Garritt Tucker, Colorado School of Mines

8:00 AM  
NOW ON-DEMAND ONLY – Atomistic Simulation of Amorphous/Crystalline Metal Composite Interface Mechanical Behavior by Nanoindentation: Amir Abdelmawla1; Thanh Phan1; Liming Xiong1; Ashraf Bastawros1; 1Iowa State University
    Here we study the plastic flow in A/C-MCs under indentation loads using molecular dynamic (MD) simulations with the aim of quantifying how the nanoscale amorphous/crystalline interface (ACI) mediates the plastic flow in such materials. The microstructure near the ACI is analyzed for six different compositions of Cu/CuZr A/C-MCs. Furthermore, the atomic deformation processes in both crystalline (C-) and amorphous (A-) phases near the amorphous crystalline interface (ACI) are investigated and correlated with the material’s overall constitutive behavior. Our major findings are: (i) the ACIs enable a co-deformation of the A- and C-phases through “stiffening” the soft phases but “softening” the stiff phases in A/C-MCs through different micro-mechanisms; (ii) there exists an ACI-induced transition zone with a thickness of ~10 nm; and (iii) the GUM population gradient is modulated by the chemical composition of the A/C-MCs. These findings may support the design of A/CMCs with unprecedented properties from the bottom up.

8:20 AM  Invited
On the Nanoscale Mechanics of Basal Dislocations in MAX Phases: Atomistic Modeling of Structure and Mobility: Gabriel Plummer1; Christopher Weinberger2; Michel Barsoum3; Garritt Tucker1; 1Colorado School of Mines; 2Colorado State University; 3Drexel University
    MAX phases, a large family of layered ternary carbides and nitrides, some of which are quite oxidation and creep resistant while also being machinable and damage tolerant. While these properties are advantageous for applications such as structural components in extreme environments, the mechanistic origins of their deformation remain relatively unknown. Newly developed interatomic potentials enable atomistic calculations of dislocation structure and mechanics. Results indicate the key role of intralayer bonding, with weak bonds favoring non-planar cores and reduced mobility. Basal dislocations also preferentially arrange as same-signed pairs on adjacent slip planes. The mobility of these pairs approaches that of dislocations in metals, a result of greater core spreading. Basal dislocations appear to be key precursors to other deformation mechanisms, such as ripplocations, kinking and delamination. These findings provide a solid foundation for further understanding MAX phase plasticity and opportunities to better engineer their deformation behavior, especially at higher temperatures.

8:50 AM  
The Evolution of Deformation Twinning in a Heterogeneous Planar Fault Energy Landscape: Ritesh Jagatramka1; Matthew Daly1; 1University of Illinois at Chicago
    Recent studies have revealed that chemical fluctuations in concentrated FCC solid solutions give rise to a “local” stacking fault energy. Our work has shown that these fluctuations extend to the entire generalized planar fault energy (GPFE) landscape, creating a spatially heterogeneous topology for the operation of deformation mechanisms. Here, we examine the implications of these fluctuations on the evolution of deformation twinning in FCC solid solutions using the kinetic Monte Carlo (kMC) method. This approach leverages calculations of the local GPFE to provide kinetically-weighted predictions for the nucleation and thickening of deformation twins. Our analysis reveals the distinct differences in morphologies that arise in solid solutions when compared to similar systems under the virtual crystal approximation. The results of this analysis are independently verified using molecular dynamics simulations. In addition, we incorporate statistical fluctuations in the GPFE into an analytical criterion that predicts the effective barriers for deformation twinning processes.

9:10 AM  
Mechanical Behavior of Free-standing and Matrix-embedded Metallic Nanoparticles at Different Temperatures: Alla Dieng1; Louise Grau1; Celine Gerard1; Jean-Claude Grandidier1; 1Institut Pprime - CNRS ISAE-ENSMA
     Nano-composite materials represent a tremendous opportunity for improving mechanical properties and/or multi-physics coupling. Nevertheless, the understanding of their deformation mechanisms is still limited, especially at lower scales. Few studies have already investigated the mechanical behavior of free-standing nanoparticles at room temperature (Bian et al 2013, Salah et al. 2017, Kilymis et al 2018, for instance). In the present work, we investigate both free-standing and embedded within a matrix nanoparticle behavior by the means of molecular dynamics simulations. Uniaxial compressions are performed on 20nm-sized nanoparticles. The impact of the force field model is first studied on aluminum nanospheres.The Ni3Al nanoparticle mechanical behavior is then investigated through a large spectrum of temperature. The plastic deformation mechanisms are analyzed in details both for free-standing and embedded in a Ni matrix nanoparticles. The effect of nanoparticle shape, crystallographic orientation or temperature on plasticity mechanisms and yield stress are discussed.

9:30 AM Break

9:50 AM  
Mechanical Behavior and Microstructure Evolution in a Nanocrystalline Tri-immiscible Alloy: Yashaswini Karanth1; Saurabh Sharma1; Billy Hornbuckle2; Kristopher Darling2; Kiran Solanki1; 1Arizona State University; 2U.S. Army Research Laboratory
    In this work, a comprehensive study of the mechanical properties and microstructural evolution of an equimolar FeCuAg tri-immiscible alloy is presented. In particular, the quasi-static and high strain-rate compressive behavior is probed to understand the role of different immiscible phases (three distinct phases) followed by advanced microstructural characterizations. The preliminary data shows anomalous material responses, i.e., the compressive stress-strain behavior indicates multiple yield points and elastic regimes with a strong strain-rate sensitive behavior. Further, the microstructure characterization using transmission electron microscopy indicates a stronger role of the Cu-Ag interface with negligible changes in Fe-phases.

10:10 AM  Invited
Nano-mechanical Behavior Associated with Dislocation-boundary Interaction Characterized though Nanoindentation and TEM In-situ Straining: Takahito Ohmura1; 1National Institute for Materials Science
    Plastic deformation behavior in the vicinity of boundaries include grain boundary and inter-phase boundary in bcc steels are characterized through nano-mechanical testing and modeled based on a dislocation-boundary interaction. The resistance to a slip transfer at the grain boundary depends on the crystallographic orientation, and is interpreted in terms of the difference in the dislocation character. Dislocations in grain interior can sink at the grain boundary of ultra-fine-grained steel, indicating a dislocation density dominancy in the extra-hardening in the UFG steel. The critical stress for plasticity initiation is lower for a semi-coherent ferrite-cementite interface than that for an incoherent one, suggesting a potential reason for the dis- and continuous yielding phenomenon in macroscopic stress-strain curve.