Advances in Multi-Principal Elements Alloys X: Structures and Modeling: Structures and Modeling I
Sponsored by: TMS Functional Materials Division, TMS Structural Materials Division, TMS: Alloy Phases Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Peter Liaw, University of Tennessee; Michael Gao, National Energy Technology Laboratory; E-Wen Huang, National Chiao Tung University; Jennifer Carter, Case Western Reserve University; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Alcoa Technical Center
Monday 8:30 AM
February 28, 2022
Room: 251B
Location: Anaheim Convention Center
Session Chair: Jeffrey Rickman, Lehigh University; Liang Qi, University of Michigan
8:30 AM
Modeling the Effect of Stress and Composition on the Stability of Lomer/Lomer-Cottrell Dislocations: Anas Abu-Odeh1; Tarun Allaparti1; Mark Asta1; 1University of California Berkeley
Lomer (L) and Lomer-Cottrell (LC) dislocations are present in many aspects of deformation in FCC metals and alloys. In particular, LC dislocations can act as effective barriers for dislocation motion, and they can act as stress concentrators for potential twin nucleation sites. Recent focus on concentrated FCC solid solution alloys has resulted in many reported observations of this dislocation and its potential role in the mechanical behavior of these alloys. However, little is understood about L and LC dislocations in concentrated alloys and how the effect of solutes changes the response of these dislocations to stress. We present atomistic simulations of L and LC dislocation cores in a model Cu-Ni system and find that the effect of chemical composition and of the orientation of the applied stress result in significantly different behaviors. These results provide new insights into mechanisms contributing to work hardening in concentrated FCC solid solution alloys.
8:50 AM
Jerky Dislocation Motion in Multi-principal Element Alloys: From Atomic Peierls Stress to Dislocation Mobility: Daniel Utt1; Subin Lee2; Yaolong Xing3; Hyejin Jeong3; Alexander Stukowski4; Sang Ho Oh3; Gerhard Dehm5; Karsten Albe1; 1Technische Universität Darmstadt; 2Karlsruhe Institute of Technology; 3Sungkyunkwan University; 4OVITO GmbH; 5Max-Planck-Institut für Eisenforschung GmbH
Dislocations in multi-principal element alloys (MPEAs) repeatedly encounter pinning during glide, leading to jerky dislocation motion. However, the origin of individual pinning points in these concentrated random alloys is a matter of debate. We investigate the origin of dislocation pinning in the prototypical Cantor (CoCrFeMnNi) MPEA and its subsystem using a combination of experiment and simulation. In-situ transmission electron microscopy studies reveal a jagged glide motion under external loading, even in the absence of elemental clustering. Our large-scale atomistic simulations reproduce the jerky dislocation motion and allow for a determination of an atomistic descriptor linking dislocation pinning sites to a local Peierls barrier. Repeated pinning of the dislocation line can be linked to local fluctuations in the atomic scale Peierls friction. We demonstrate that the spatial density of high local Peierls barriers is proportional to the critical stress required to initiate dislocation glide and inversely linked to the dislocation mobility.
9:10 AM Invited
Energy Landscape of Deformation Twinning in Multi-principal Elements bcc Alloys: Liang Qi1; Shih-Kuang Lee1; 1University of Michigan
Deformation twinning can be an important plastic deformation mechanism for multi-principal elements body-centered cubic (bcc) alloys, such as metastable beta Ti alloys. In this study, we apply first-principles-based calculations to determine the energy landscape of {112} and other deformation twinning modes in multi-principal elements bcc alloys that contain Ti. Supercells of alloys with different compositions are constructed either by special quasirandom structures (SQS) structures to simulate solid solutions or Monte Carlo simulations to consider the short-range ordering (SRO). Different numbers of twin embryo layers in these supercells are investigated to determine their formation and migration energies. The stability of these twin embryos is also compared with the embryos of other possible metastable phases. These energy landscape results are used to explain the competitive mechanisms between different modes of deformation twinning and formation of metastable phases in multi-principal elements bcc alloys as the function of chemical compositions and electronic structures.
9:30 AM
Critical Shear Stress Distributions and Dislocation Mobility in FeNiCrCoCu High Entropy Alloys via Atomistic Simulations: Yixi Shen1; Douglas Spearot1; 1University of Florida
The critical shear stress necessary to initiate dislocation movement and the relationship between shear stress and velocity, known as a dislocation mobility law, is investigated in FeNiCrCoCu high entropy alloys (HEAs) using atomistic simulations. First, Monte Carlo calculations show that chemical short-range order is minimal in this HEA with equiatomic composition, which makes it ideal to study the influence of local distortion. Then, molecular statics calculations show that critical shear stresses to unpin a dislocation are found to have a large spread, with mean value of 96MPa and a standard deviation of 63MPa for a screw dislocation. Details associated with dislocation mobility laws are found to be unique in HEAs. For example, phonon damping coefficients in the HEA do not show linear dependence on temperature. Significant waviness in the leading and trailing partial dislocations is observed in HEAs and is correlated with the ability of individual dislocations to glide.