Integration between Modeling and Experiments for Crystalline Metals: From Atomistic to Macroscopic Scales II: Session II
Program Organizers: Arul Kumar Mariyappan, Los Alamos National Laboratory; Irene Beyerlein, University of California, Santa Barbara; Levente Balogh, Queen's University; Josh Kacher, Georgia Institute of Technology; Caizhi Zhou, University of South Carolina; Lei Cao, University of Nevada

Tuesday 2:00 PM
November 3, 2020
Room: Virtual Meeting Room 35
Location: MS&T Virtual

Session Chair: Qian Yu, Zhejiang University; Scott Mao, University of Pittsburgh


2:00 PM  Invited
Twinning Nucleation in Hexagonal Close-packed Crystals: Yang He1; Scott Mao1; Zhengwu Fang1; 1University of Pittsburgh
    Design and processing of advanced lightweight structural alloys based on magnesium and titanium rely critically on a control over twinning which, however, remains elusive to date and is dependent on an explicit understanding on the twinning nucleation mechanism in hexagonal close-packed (HCP) crystals. This talk will be the in-situ high resolution transmission electron microscopy for studying the twinning nucleation in HCP crystals. The {10-12} twinning nucleation process in HCP rhenium nanocrystals is directly observed and a novel “dual-step” twinning nucleation mechanism is proposed accordingly. The findings provide much-needed high-resolution evidences to the twinning nucleation mechanism in HCP crystals, with crucial implications for engineering advanced structural alloys.

2:30 PM  Cancelled
Twin Transmission Across Grain Boundaries in HCP Metals: Arul Kumar Mariyappan1; Rodney McCabe1; Laurent Capolungo1; Carlos Tome1; 1Los Alamos National Laboratory
    Deformation twinning is a prevalent plastic deformation mode in hexagonal close packed metals due to a lack of available and easily activated crystallographic slip modes. Propagation of twins across grain boundaries is referred as twin transmission. This process may continue over several grains and develops twin chains. Twin transmission across grain boundaries enhance cracking along twin boundaries and leads to premature failure. Though twinning has been studied over several-decades, almost all the reported studies treat twinning as a two-dimensional event. Recent studies report that the lateral twin propagation is relatively easy compared to forward or normal propagation. Here we performed statistical EBSD analysis of twin sections, and full-field crystal-plasticity modeling to study the forward and the lateral transmission of {1012} twins into neighboring grains in magnesium. We found that the lateral transmission is relatively easy compared to the forward transmission, which is explained and interpreted using the calculated local stresses.

2:50 PM  
On the Characterization of Twin-twin Interactions in Mg and Its Alloys: Yanqing Su1; Irene Beyerlein2; 1Utah State University; 2University of California, Santa Barbara
    In Mg and some of its alloys, twinning and detwinning play an important role in their plastic deformation at room temperature, because their hexagonal-close packed (HCP) structures have a limited number of activated slip systems. Between two twins that are close to each other, it is known that there exists a critical spacing less than which their interactions become non-negligible. However, the influences of the twin thicknesses have not been investigated. Here, using a fully-field, crystal plasticity-based fast Fourier transform approach, we explore the interactions between two twins of parallel or non-parallel in Mg and its alloys while systematically varying the twin thickness. By quantifying these twin-twin interactions, our results provide insights into the underlying mechanisms of deformation twinning in HCP metals and alloys.

3:10 PM  
Directionally-anisotropic Mobility of Faceted Boundaries Explained through Interfacial Dislocation Mechanisms: Megan McCarthy1; Timothy Rupert1; 1University of California, Irvine
    Faceted grain boundaries, or interfaces which increase their surface area to lower their net energy, have unusual structures that influence migration in unexpected ways. Some of these interesting behaviors, such as antithermal mobility, are correlated with grain boundary dislocation activity within facet planes and junctions. In this talk, we explore how Shockley partial dislocation emission affects the migration of faceted Σ11 <110> tilt bicrystal boundaries in various pure and doped FCC metals using molecular dynamics and an artificial driving force. We find that Shockley partial dislocations at junctions can lead to boundary migration velocities that differ depending on the migration direction. This directionally-anisotropic mobility can be influenced by changes in material, temperature, and dopant concentration, which each alter boundary dislocation activity during migration. Finally, the potential impact of this type of anisotropy on the coarsening of a polycrystalline grain boundary network is also investigated.

3:30 PM  Invited
Texture Evolution of Individual Layers during Accumulative Roll Bonding of Fe-Cu Metallic Laminates: Rodney McCabe1; Miroslav Zecevic1; Thomas Nizolek1; Matthew Schneider1; Cody Miller1; Carl Osborn1; Daniel Coughlin1; Ricardo Lebensohn1; Johh Carpenter1; 1Los Alamos National Laboratory
    Accumulative roll bonding (ARB) is used to produce bulk bimetallic laminates with average layer thicknesses from hundreds of microns to tens of nanometers and corresponding logarithmic strains ranging from 0.7 to 12. The roll-bonding steps involve rolling reductions greater than 50% resulting in non-uniform strain in the plate and texture variations from layer to layer through the ARB plate. We study the texture evolution of individual layers in ARB processed Fe-Cu metallic laminates using EBSD and the viscoplastic self-consistent model coupled with finite elements (FE-VPSC). We show that layers near the center of the plate evolve towards typical fcc and bcc rolling texture components while layers near the surface develop other texture components. The simulations allow us to examine the degree to which layer deformation history affects the overall texture during continued processing (i.e. an outer layer during one bonding step may become an inner layer during subsequent bonding steps).