Integration between Modeling and Experiments for Crystalline Metals: From Atomistic to Macroscopic Scales IV: Session II
Sponsored by: TMS Advanced Characterization, Testing, and Simulation Committee, TMS Materials Characterization Committee, TMS: Nanomaterials Committee
Program Organizers: Arul Kumar Mariyappan, Los Alamos National Laboratory; Irene Beyerlein, University of California, Santa Barbara; Levente Balogh, Queen's University; Caizhi Zhou, University of South Carolina; Lei Cao, University of Nevada; Josh Kacher, Georgia Institute of Technology
Monday 2:00 PM
October 10, 2022
Room: 401
Location: David L. Lawrence Convention Center
Session Chair: Yue Fan, University of Michigan; Siddhartha Pathak, Iowa State University
2:00 PM Invited
Evolution of Metastable Grain Boundaries and Their Tunability under Extreme Conditions: Yue Fan1; Zhitong Bai1; 1University of Michigan
In ultrafine-grained materials and under non-equilibrium processing conditions, GBs are rarely in ground states and would instead present a multiplicity of microscopic metastable states, endowing the system with enhanced tunability. For example, recent experiments show nanocrystals can be rejuvenated by femtosecond laser and their hardness can be effectively controlled. However, a mechanistic understanding on metastable GBs’ evolution remains unclear. Here we investigate a variety of metastable GBs under fast driving conditions using atomistic simulations. Assisted with data-mining algorithm to analyze the annealing behavior of GBs at various conditions, we construct a high-fidelity energetic evolution map, showing that it can be divided into an ageing regime and a rejuvenating regime over the energy—temperature space. The ageing/rejuvenating stems from the energy imbalance during the interchanges between metastable states, and a kinetic equation is subsequently derived. The predicted energetic evolution and its implication on metastable GBs’ mechanical performance are consistent with experiments.
2:30 PM
A Grain Boundary Dislocation-density-based Crystal Plasticity Model for FCC Nanocrystalline Metals: Jonathan Cappola1; Jian Wang2; Lin Li1; 1University of Alabama; 2University of Nebraska-Lincoln
A dislocation-density-based crystal plasticity model for nanocrystalline FCC metals is developed based on the thermally-activated mechanism of dislocations depinning from grain boundaries (GBs). Dislocation slips originating from GB sources are assumed to be the controlling deformation mechanism with the dislocation density being formulated as a boundary term and subsequently smeared over the grain volume uniformly. This leads to the kinematic enforcement of grain-uniform plastic deformation. Dislocation density evolution thereby involves the creation of mobile dislocations from GB ledges, and recovery via diffusion. This model allows for the evolution of the GB character, related to initial processing/production, to be computed as a direct result of dislocation-mediated plasticity. The influence of initial dislocation density distribution, along with its evolution, is investigated to in context of softening/hardening behaviors observed in bulk nanocrystals, the breakdown of Hall-Petch, and the effect of processing routes on the resulting bulk nanocrystals' mechanical properties.
2:50 PM
Continuum Dislocation Dynamics-based Full Field Crystal Plasticity Modeling for Characterizing Dislocation Distribution and Boundary Transmission in Polycrystalline Materials: Navid Kermanshahimonfared1; Georges Ayoub2; Ioannis Mastorakos3; 1Clarkson University ; 2University of Michigan; 3Clarkson University
In this work, a continuum dislocation dynamics (CDD)-based crystal plasticity simulations were achieved using a fast Fourier transform-based elasto-viscoplastic (EVP-FFT) micromechanical solver to analyze the deformation mechanisms of three different polycrystalline metals. The stress/strain gradient theory (CDD) combined with the crystal plasticity allows accounting for the grain size effects, dislocation density flux among neighboring grains and grain boundary back stress field. The simulations were performed on 3D microstructures of α-Iron and aluminum obtained using electron backscatter diffraction-based orientation image microscopy. A robust parameter identification method is proposed, to fit the macroscopic mechanical behavior and texture evolution. Finally, the mechanisms of deformation are studies at different location of the polycrystalline materials and for different loading conditions.
3:10 PM
Motions in Cylindrical Grain Boundaries: Anqi Qiu1; Ian Chesser2; Elizabeth Holm1; 1Carnegie Mellon University; 2George Mason University
Isolated cylindrical grain boundaries in embedded bicrystal systems shrink spontaneously under curvature driving force at high temperatures. With molecular dynamics simulations, it was found that the reduced mobility, a measure of grain boundary migration rate, is greatly affected by the initial velocity seed, which was unexpected in atomistic simulations. Under an externally applied synthetic driving force (SDF) opposite of the curvature driving force, cylindrical grain boundaries expand, and in some cases, facet. The orientations of the facets formed by a given initial grain boundary orientation are invariant of the driving force magnitude, temperature, and initial grain size. The expanding motions of cylindrical grain boundaries are also affected by initial velocity seeds, given that all other conditions are the same. In this study, the shrinking and expanding motions of isolated cylindrical grain boundaries are explored in depth, which will give more insights into the mechanisms of grain boundary migration.
3:30 PM Break
3:50 PM Invited
In Situ Studies on Room Temperature Deformability of Nanolaminates and Nanocrystalline Intermetallics: Xinghang Zhang1; Ruizhe Su1; Dajla Neffati2; Yashashree Kulkarni2; Nick Richter1; 1Purdue University; 2University of Houston
Interfaces play an important role on deformation mechanisms of metallic materials with nanoscale microstructures. In this presentation, we will cover two examples of nanostructured materials. In the first example, we will compare the deformation behavior of three Cu/Co multilayer systems with identical layer thickness but different types of layer interfaces. In situ SEM micropillar compression tests show that the three systems have drastically different mechanical behaviors. Molecular dynamics (MD) simulations reveal an unexpected interplay between pre-existing twin boundaries, stacking faults, and incoherent layer interfaces. In the 2nd example, we present a deformable nanocrystalline CoAl intermetallics. In situ studies show that nanocrystalline CoAl exhibits ultra-high yield strength and prominent work hardening ability. TEM studies combined with MD simulations reveal unique deformation mechanisms of the nanocrystalline intermetallics.
4:20 PM
Slip Transmission and Voiding during Slip Band Intersections in Fe70Ni10Cr20 Stainless Steel: Xiaowang Zhou1; Richard Skelton1; Ryan Sills2; Christopher San Marchi1; 1Sandia National Laboratories; 2Rutgers University
Slip transmission through interfaces fundamentally determines mechanical properties of crystalline materials. Molecular dynamics simulations of eight band intersections in Fe70Ni10Cr20 alloys revealed that secondary bands always transmit into epsilon bands more easily than into twin bands. While this is surprising because the epsilon-phase has a different crystal structure from the matrix, our finding that twins do not possess easy crystallographic pathways for transmission explains this phenomenon. We also found that the band intersection regions preferentially nucleate voids. These provide guidelines to understand materials. For example, since hydrogen promotes epsilon-bands, our findings can help understand hydrogen compatibility.