HEA 2023: Fundamental Theory and Modeling II
Program Organizers: Andrew Detor, DARPA/DSO; Amy Clarke, Los Alamos National Laboratory
Monday 1:40 PM
November 13, 2023
Room: Three Rivers
Location: Omni William Penn
Session Chair: Sofia Sheikh, Texas A&M University
1:40 PM Introductory Comments
1:45 PM Cancelled
Multi-scale Modelling of Multiple-principal Element Alloys: From Electrons to Atoms to Continuum using Machine Learning: Shyue Ping Ong1; Hui Zheng1; Lauren Fey2; Irene Beyerlein2; 1University of California-San Diego; 2University of California, Santa Barbara
Refractory multi-principal element alloys (RMPEAs) are promising for high-temperature structural applications. In this talk, I will discuss how multi-scale modeling of RMPEAs from electrons to atoms to continuum can be achieved with recent advances in machine learning (ML). Using the MoNbTi and TaNbTi RMPEAs as examples, we investigate the role of short-range ordering (SRO) on dislocation glide. An accurate ML interatomic potential (MLIP) was developed using DFT calculations. Monte Carlo/molecular dynamics simulations with the MLIP show that MoNbTi exhibits a much greater degree of SRO than TaNbTi, and the local composition directly affects the unstable stacking fault energies (USFEs). These atomistic simulations were then used to parameterize a phase-field dislocation dynamics (PFDD) model. From PFDD simulations, we find that the gliding dislocations experience significant hardening due to pinning and depinning caused by random compositional fluctuations, with higher SRO decreasing the degree of USFE dispersion and hence, the amount of hardening.
2:15 PM
Dislocations in Complex Alloys:
Insights from Peierls-Nabarro Modeling
: Terrence Moran1; Bastien Aymon1; William Curtin1; 1Swiss Federal Institute Of Technology
Dislocations in alloys with random solute distributions, short-range order, or clustering have a range of competing length and energy scales that overall establish energy barriers to dislocation motion. The flow behavior then depends on many different underlying material parameters and it becomes difficult to formulate theories that include all these factors. Here, to guide development of theories, we show how a Peierls-Nabarro/Phase-Field (PN/PF) model can enable efficient and accurate parametric exploration of dislocation behavior as a function of controllable material parameters. Key often-overlooked elements of the PN/PF model are discussed. First applications of the PN//PF model to (i) understanding dislocation line tension in both fcc and bcc metals and (ii) the emergence of characteristic dislocation length scales in random alloys, are then presented and discussed in the context of current theories.
2:35 PM
Investigating Alloying Element Effects on Screw Dislocation Trajectories in Multicomponent bcc Alloys: Amir Hassan Zahiri1; Liang Qi1; 1University of Michigan
This research explores the impact of alloying elements, particularly Hf and/or Ti, on the slip behavior of Nb and Ta-based multicomponent solid solution alloys with a body-centered cubic (bcc) crystal structure using molecular dynamics (MD) simulations. The study compares different binary and multicomponent bcc alloys under shear deformation. Without alloying elements, the a/2<111> screw dislocation's slip plane changes from the {110} plane to the {112} twinning slip plane in both pure Nb and Ta. However, with the addition of Hf and Ti, the slip plane transitions from the {112} twinning slip plane to the {110} slip plane at intermediate concentrations of alloying elements. At high concentrations, the slip plane shifts to the {112} anti-twinning slip plane. These transitions depend on strain rates, temperatures, and the stability of metastable phases. Understanding these slip plane transitions can improve the mechanical properties of bcc multicomponent alloys by reducing strain localization and enhancing ductility.
2:55 PM Cancelled
Simulations and Modelling of the High Temperature Yield Behavior of BCC Refractory Complex Concentrated Alloys (RCCA’s): Satish Rao1; Brahim Akdim2; Oleg Senkov1; Daniel Miracle3; Todd Butler3; 1Mrl Materials Resources Llc; 2UES Inc; 3AFRL
Atomistic simulations, using Johnson-Zhou and/or Machine learning potentials, of the core structure and mobility of ½[111] screw, edge and mixed dislocations in complex concentrated BCC alloys are presented. The core structure and its variations obtained for screw dislocations in NbTiZr using atomistic simulations are compared with first-principles calculation results and good agreement is found. Average solute-dislocation core interaction energies are used to determine the critical stress for the motion of screw dislocations as a function of temperature using Rao- Suzuki model In addition, diffusional effects at very high temperatures on the predicted yield behavior are modelled. Edge dislocation mobilities in these alloys are modelled using the Maresca-Curtin model. Experimental and molecular dynamics yield data for MoNbTaW are analyzed using Rao-Suzuki model as well as Maresca-Curtin model. The model results on yield behavior are shown to be in good agreement with experimental data in selected BCC complex concentrated alloys.
3:15 PM Break
3:35 PM
Screw and Edge Dislocation Strengthening in BCC High Entropy Alloys, and Efficient Yield Strength Prediction: Francesco Maresca1; William Curtin2; 1University of Groningen; 2Brown University
We introduce and validate a holistic, parameter-free strengthening theory of screw and edge dislocations in BCC high entropy alloys. In contrast with screw-controlled pure BCC metals, in non-dilute BCC alloys both edge and screw dislocations are pinned due to strong local energy fluctuations. Thus, three strengthening regimes are found in screws: (1) low-temperature, Peierls-barrier controlled strength; (2) intermediate-temperature strength, due to kink migration over barriers scaling with solute/dislocation interaction; (3) high-temperature strength, scaling with energy of vacancy and self-interstitials forming after unpinning of cross-kinks. Edge dislocation strengthening scales with misfit volumes and elastic moduli. The edge theory is cast in an analytical form that is parameter-free and depends on physical quantities that can be determined ab-initio or experimentally. The reduced edge theory enables screening over 10 million compositions in the whole Al-Cr-Mo-Nb-Ta-W-V-Ti-Zr-Hf alloy family to find the strongest BCC HEAs.
3:55 PM
Strength Reductions of Metal Alloys with Short-range Order as Revealed by Atomistic Simulations: Xin Liu1; William Curtin1; 1EPFL
A theory for strengthening for multicomponent non-dilute alloys possessing short-range order (SRO) has recently been developed. The theory predicts that, in addition to athermal strengthening, there is a notable effect of SRO on the solute-dislocation interactions that can change the strength relative to a random alloy. Atomistic simulations in a model binary NbW alloy are used to demonstrate that alloy strength due to solute-dislocation interactions can be increased or decreased depending on the SRO. Specifically, SRO is introduced using fictitious solute-solute interactions and the Nudged Elastic Band method is used to compute the energy barriers for edge dislocation motion. Energy barriers can be decreased when the SRO parameters are negative. The theoretical predictions for the same system are in reasonable quantitative agreement with the simulation results. These findings demonstrate the unexpected possibility of reduced strength due to SRO and validate the analytical theory as a tool to guide alloy design.
4:15 PM
Investigating the Stability of a Al0.5NbTa0.8Ti1.5V0.2Zr BCC/B2 RCCA: Julian Brodie1; Junxin Wang1; Jean-Philippe Couzinie2; Milan Heczko1; Veronika Mazanova1; Michael Mills1; Maryam Ghazisaeidi1; 1Ohio State University; 2University Paris-Est Créteil (UPEC) - IUT
Recently, the AlNbTaVTiZr class of BCC/B2 Refractory Complex Concentrated Alloys (RCCAs) have drawn increased interest as the bcc analogue to the well-known Ni-based super alloys with gamma/gamma’ microstructure. Previous experimental results on the microstructure of these alloys have been varied where some have found the formation of brittle phases within the BCC matrix along with the B2 precipitates. Since the mechanical properties of these alloys are highly dependent on their microstructure, it’s crucial to understand why these phases form. We use Density Functional Theory to study the phase stability of the B2 phase in a BCC/B2 Al0.5NbTa0.8Ti1.5V0.2Zr RCCA. We calculate the formation energy using DFT and study the effects of non-equilibrium conditions, such as temperature and strain, on the competing phases. We also explain how the microstructure is unstable and is prone to transform into an Omega, tetragonal, or hexagonal phase.
4:35 PM
Testing the Origin of the High Strength of Complex Concentrated Alloys using Large-scale Molecular Dynamics Simulations: Vasily Bulatov1; Xinran Zhou2; Jaime Marian2; 1Lawrence Livermore National Laboratory; 2University of California Los Angeles
We report results of large-scale Molecular Dynamics simulations of plastic flow in single crystalline complex alloys subjected to high-rate compression and tension over a wide range of compositions, temperatures and straining rates. Utilizing several sets of interatomic potentials previously developed for multi-component metal alloys, our simulations are defined to test applicability of popular analytical models of strengthening in complex multi-component alloys and, at the same time, to reveal full details of dislocation motion mechanisms contributing to strengthening.
4:55 PM
Predicting Yield Strength of High Entropy Alloys from Density Functional Theory: Siming Zhang1; Guofeng Wang1; 1University of Pittsburgh
To enable rational design of high entropy alloys (HEAs), we have developed a first principles density functional theory based computational approach to predict the yield strength of single phase HEAs. Specifically, we applied the developed method to calculate the yield strength of some select HEAs with face-centered cubic (fcc) or body-centered lattice (bcc) structure and with varying chemical composition. We have examined our computational approach for four fcc alloy systems, i.e., NiCoFe, CoCrFeNi, CoCrFeCuNi, and RdIrPdPtNiCu, and four bcc alloys systems, i.e., MoNbTaW, MoNbTaV, AlCoCrFeNi, and AlCoCrFeNiZr0.3. For these HEAs with dramatically different chemical composition, our predicted yield strengths are found to agree well with experimental values. Consequently, we have demonstrated that the developed first principles based computational approach is a reliable computational tool for understanding the composition-structure-property relation of HEAs and, particularly, exploring novel HEAs with superior mechanical properties over vast composition space.