High Entropy Materials: Concentrated Solid Solution, Intermetallics, Ceramics, Functional Materials and Beyond: Theory and Fundamentals
Sponsored by: ACerS Basic Science Division, TMS Alloy Phases Committee
Program Organizers: Xingbo Liu, West Virginia University; Michael Gao, National Energy Technology Laboratory; Peter Liaw, University of Tennessee; Jian Luo, University of California, San Diego; Yiquan Wu, Alfred University; Yu Zhong, Worcester Polytechnic Institute
Tuesday 2:00 PM
November 3, 2020
Room: Virtual Meeting Room 33
Location: MS&T Virtual
Session Chair: Jamie Morris, Ames National Laboratory; Guofeng Wang, University of Pittsburgh
2:00 PM Invited
Lattice-distortion-enhanced-yield Strength in a Refractory High-entropy Alloy: Chanho Lee1; Yi Chou2; George Kim3; Michael C. Gao4; Ke An5; Chuan Zhang6; Wei Chen3; Jonathan D. Poplawsky5; Gian Song7; Yi-Chia Chou2; Peter Liaw; 1University of Tennessee; 2National Chiao Tung University; 3Illinois Institute of Technology; 4National Energy Technology Laboratory; 5Oak Ridge National Laboratory; 6Computherm, LLC; 7Kongju National University
Severe lattice distortion is one of the four core effects proposed in single-phase high-entropy alloys (HEAs) and contributes significantly to the yield strength. However, the connection between the atomic-scale lattice distortion and macro-scale mechanical properties through experimental verifications has yet to be fully achieved, owing to two critical challenges: (1) the difficulty in the development of homogeneous single-phase solid-solution HEAs, and (2) the ambiguity in describing the lattice distortion and related measurements and calculations. We have designed and developed the single-phase body-centered-cubic (BCC) refractory HEA, NbTaTiVZr, using thermodynamic modeling coupled with experimental verifications. Compared to our previously-developed single-phase NbTaTiV HEA, the NbTaTiVZr refractory HEA shows a higher yield strength without significant change in the microstructures after the addition of the Zr element. The increase in yield strength is systematically and quantitatively studied in terms of lattice distortion using a theoretical model, first-principles calculations, and experimental verifications.
2:20 PM Invited
Atomistic Modeling Predictions of the Structures and Properties of High Entropy Alloy Nanoparticles from Carbothermal Shock Synthesis: Guofeng Wang1; Zhenyu Liu1; 1University of Pittsburgh
To address the structural complexities of high entropy alloys (HEAs), we have developed and applied atomistic modeling methods to predict the structures and properties of HEA nanoparticles. In our calculations, the interatomic interactions were described with the modified embedded atom method (MEAM). Using a combined molecular dynamics (MD) and Monte Carlo (MC) simulations, we investigated the formation of solid solution phase in Co0.12Ni0.14Ru0.43Rh0.30, Ru0.44Rh0.30Co0.12Ni0.14, and Ru0.25Rh0.25Co0.2Ni0.2Ir0.1 nanoparticles with size ranging from 2 to 5 nm. Moreover, we used the different duration between MC and MD simulations to model slow annealing and fast quench processes. Our simulation results indicated that the local severe lattice distortion could block the diffusion of atoms and hence lead to a stable solid solution phase during a carbothermal shock synthesis procedure. Consequently, we have demonstrated that atomistic simulation techniques as useful methods for understanding the composition-structure-property relation of novel high entropy alloys.
2:40 PM Invited
Phase Stability of CoCrFeMnNi High Entropy Alloy at Elevated Temperature and Pressure: Sitaram Aryal1; Lizhi Ouyang1; Michael Gao2; 1Tennessee State University; 2NETL
Temperature and pressure dependent phase stability of CoCrFeMnNi equimolar high entropy alloy (HEA) was investigated using methods based on density functional theory. The BCC and HCP phases of the CoCrFeMnNi HEA models were constructed using the special quasirandom structure method. Temperature and pressure dependent free energies of the HEA models were computed using the G(p,T) package. Phase stability, mechanical properties and other thermodynamic properties of these models will be presented. Additionally, local strain evolution under temperature and pressure will be discussed.
3:00 PM
Rapid Production of Accurate Multicomponent Embedded-Atom Method Potentials for Metal Alloys: Elan Weiss1; Cosmin Safta2; Habib Najm2; David Riegner1; Logan Ward1; Wolfgang Windl1; 1The Ohio State University; 2Sandia National Laboratories
A critical limitation to the wide-scale use of classical molecular dynamics remains the limited availability of suitable interatomic potentials. This becomes more severe if one considers the limited pool of ternary and higher order potentials. We introduce the “Rapid Alloy Method for Producing Accurate General Empirical Potentials” (RAMPAGE), a computationally economical procedure to generate binary potentials from already-existing elemental EAM potentials. By using published potentials, the cross-interaction terms can be fitted efficiently with small training sets generated via DFT. Importantly for concentrated solid solutions, RAMPAGE potentials can be combined into multi-component potentials with no additional fitting. We demonstrate the surprising accuracy of RAMPAGE potentials in modeling key properties of alloys in comparison to potentials created using larger training sets. Using Bayesian statistics, we benchmark the quality of RAMAPAGE potentials with respect to static equilibrium properties as well as properties of equilibrium liquids, solid solutions, and metallic glasses.
3:20 PM
Bond-order Bond Energy Model for Concentrated Solid Solutions: Szu-Chia Chien1; Christian Oberdorfer1; Wolfgang Windl1; 1Ohio State University
We introduce a novel way to parameterize random-alloy energies in the form of a bond-order bond energy model. There, a bond order function models the transition between competing phases or bond types and switches their respective bond energies on and off. We first demonstrate this on the example of the Ni-Cr-Mo alloy system and then move to Cantor-type concentrated solid solution systems. We show that the bond-order bond energy model can predict phase diagrams with excellent accuracy in a simple fashion. We also show that bond-energies define quantitative, composition-dependent chemical potentials in a natural way, allowing to efficiently calculate configuration-optimized alloy vacancy formation energies. As proposed by the concept of the extended Gibbs adsorption isotherm, alloying decreases formation energies, where values smaller than zero indicate thermodynamic instability of the underlying crystal. With that, the bond-order bond energy model provides an intuitive holistic picture that unites defect and phase stability.
3:40 PM
Atomistic Simulations Evince the Sluggish Diffusion in Refractory HEAs: Ankit Roy1; Joydeep Munshi1; Ganesh Balasubramanian1; 1Lehigh University
HEAs have attracted significant attention due to excellent mechanical properties at elevated temperatures. While below the transition temperature the primary resistance to deformation is gained through solid solution strengthening in HEAs, the resistance to creep deformation above transition temperature is governed by atomic diffusion. Despite its significance in manufacturing industries, investigating diffusion at elevated temperatures is experimentally difficult due to measurements and oxidation issues. We employ molecular dynamics with first principles to examine atomic diffusion in a refractory HEA comprising of Mo-Ta-Ti-W-Zr. The results reveal that diffusion in HEAs near melting temperature is several orders of magnitude smaller than diffusion in reference metals in the pure state providing evidence of high creep resistance responsible for excellent mechanical properties at elevated temperatures. A deeper investigation reveals that the formation of low energy atomic traps in the lattice of HEAs increases the energy required for an atom to migrate to a vacancy.
4:00 PM Invited
High Entropy and Sluggish Diiffusion Effects in Co-Cr-Fe-Ni Based High Entropy Alloys: Abhishek Mehta1; Yongho Sohn1; 1University of Central Florida
High entropy and sluggish diffusion effects were investigated using solid-to-solid diffusion couple approach in Co-Cr-Fe-Ni base alloys. High entropy effect was examined in off-equiatomic compositions of Al-Co-Cr-Fe-Ni and Al-Co-Cr-Fe-Ni-Mn, generated by diffusion of Al and Ni in equiatomic CoCrFeNi and CoCrFeNiMn alloys. Thermodynamic stability (i.e. ΔH, –TΔS, and ΔG) of off-equiatomic compositions were compared to those of equiatomic compositions determined using pseudo-binary phase diagram. Due to the contribution from the enthalpy of mixing, a higher thermodynamic stability was determined for the off-equiatomic compositions than their equiatomic counterpart. Sluggish diffusion effect was examined by measuring interdiffusion and tracer diffusion coefficients in CoCrFeNi, CoCrFeNiMn, and Al0.25CoCrFeNi alloys. Comparison to solvent based traditional alloys suggest that diffusion is not always sluggish in high entropy alloys. Application of potential energy fluctuation model suggest that the larger fluctuation in lattice potential energy may not always result in sluggish diffusion kinetics.
4:20 PM
Effect of Grain Size and Strain Rate on the Deformation Mechanism of Nanocrystalline HEAs Using Molecular Dynamics Simulations: Ankit Roy1; Ganesh Balasubramanian1; 1Lehigh University
HEAs have garnered notable interest since their inception due to their potential for maintaining excellent mechanical properties at high temperatures. Though their mechanical properties have been well investigated, the effect of grain size and deformation rate on its properties are yet to be explored. Most HEAs follow the Hall-Petch relation at the micron level grain size, but the Hall-Petch relation breaks down below a critical grain size in nanocrystalline HEAs. Below the critical grain size, materials follow an inverse Hall-Petch relation where strength does not increase with reducing grain size but instead, flow stress maintains a linear relation with d-1/2, where d is the average grain diameter. In parallel, the effect of increasing strain rate is studied on a fixed grain size and an increase in stress strain gradients is noted. The switching of deformation mechanism from slip to grain boundary slide is the primary factor responsible for these phenomena.