High Entropy Alloys IX: Structures and Modeling
: Structures and Modeling II
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; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Globus Medical
Monday 2:00 PM
March 15, 2021
Room: RM 9
Location: TMS2021 Virtual
Session Chair: Diana Farkas, Virginia Polytechnic Institute; Irene Beyerlein, University Of California, Santa Barbara
2:00 PM Invited
Mechanisms of Short-range Ordering and Cluster Formation and their Effects on Mechanical Properties of High-entropy Alloys: Shuai Chen1; Zachary Aitken1; Subrahmanyam Pattamatta2; Zhaoxuan Wu2; Zhi-Gen Yu1; Rajarshi Banerjee3; David Srolovitz2; Peter Liaw4; Yong-Wei Zhang1; 1Institute of High Performance Computing, A*STAR; 2City University of Hong Kong; 3University of North Texas; 4University of Tennessee
We investigate two high-entropy alloys (HEAs), CoCuFeNiPd and CoCuFeNiTi, using a combination of Monte Carlo and molecular dynamic (MD) simulations. Our results show that CoCuFeNiPd exhibits much stronger atomic segregation and short-range ordering (SRO) than CoCuFeNiTi, despite the larger differences in the relative atomic size and electronegativity of Ti with other constituent elements, as compared to Pd, suggesting that the differences in atomic size and electronegativity alone are insufficient to explain the difference. We find that it is the chemical-affinity disparity and exclusivity between Ti (Pd) with the remaining species that lead to the different SRO and cluster formation in these two HEAs. We also examine their mechanical properties at different degrees of SRO and find that SRO and cluster formation are able to enhance yielding strength without sacrificing ductility. Our findings are consistent with existing experiments, and highlight the importance of SRO in influencing the mechanical properties of HEAs.
2:25 PM Invited
Development of Interatomic Potentials to Model the Deformation Behaviors in Highly Concentrated/Entropy-stabilized Ni-base Superalloys: Ridwan Sakidja1; Andrew Duff2; Wai-Yim Ching3; Caizhi Zhou4; 1Missouri State University; 2STFC; 3University of Missouri-Kansas City; 4University of South Carolina
We developed interatomic potentials designed for a selected number of multi-component, highly concentrated or entropy-stabilized Ni-based Superalloys. The overall approach is based on the Reference-free Modified Embedded Atom Method via MEAMFIT code whereby energy, stress and force samplings mostly from ab-initio molecular dynamics (AIMD) simulations were extracted for the parameterization processes. By focusing the concentration regime at or near the vicinity of high-entropy alloys (HEA), we were able to extend the applicability and transferability of the potentials toward a wider scope of alloy compositions including the highly concentrated and commercially-relevant Ni-based Superalloys. The support from DOE-NETL under the award No. FE0031554 is gratefully acknowledged.
2:50 PM Invited
Structural Essentiality for Plasticity of High-entropy Alloys Profiled by Data Mining: Wei-Ren Chen1; Chi-Huan Tung2; Shou-Yi Chang2; Yue Fan3; Zhitong Bai3; Changwoo Do1; 1Oak Ridge National Laboratory; 2National Tsing Hua University; 3University of Michigan
Existing studies have indicated the close link between the microstructure and mechanical behaviors of HEAs. How their configurational features influence the local plastic activity has not been answered unambiguously. Using atomistic simulations, we investigate the equilibrium structure of the CrMnFeCoNi HEA system. The local configurational features are first quantified by a gyration tensor weighted by local electronegativity and classified by principal component analysis. We found that the compositional difference only alters the mean inter-particle distance but has no influence on other configurational features including orientation and shape. Moreover, the local plastic activity is likely to take place in the spatial region characterized by low electronegativity. Linear discriminant analysis further provides evidence which demonstrates that the exact location of mechanical failure is determined by the compatibility between the orientation of local configuration units and the direction of applied stresses. Our computational findings shed new light on understanding the plasticity of HEA.
3:15 PM Invited
Deformation Behavior of a Model High Entropy Alloy from Atomistic Simulations: Diana Farkas1; 1Virginia Polytechnic Institute
This paper reports atomistic simulation studies of deformation behavior in a model quinary high entropy FCC alloy. The simulations are based on empirical interatomic potentials and use massively parallel molecular dynamics techniques at the atomistic level to study the deformation mechanisms. Virtual tensile tests were performed and the material response and the results are compared with a corresponding “average atom” material that has the same average properties but no local randomness. We find that the main effect of the random composition fluctuations is to make dislocation glide more difficult. The complex high entropy alloy presents a higher strength, mostly driven by the fact that the dislocations emitted from the grain boundaries do not glide as easily in the random alloy. Simulations of fracture propagation are also presented, showing a higher fracture resistance in the HEA material than in the corresponding material without compositional fluctuations.
3:40 PM
Phase-Field Dislocation Dynamics Modeling of Refractory Multi-Principal Element Alloys: Lauren Fey1; Abigail Hunter2; Irene Beyerlein1; 1University Of California, Santa Barbara; 2Los Alamos National Laboratory
Refractory multi-principal element alloys are of great interest to the materials community due to their potential for high-temperature applications. However, there is still debate over the dominant deformation and strengthening mechanisms. We use phase field dislocation dynamics to study the behavior dislocations within these alloys, accounting for varying dislocation core structures and differences between screw and edge mobility. We also consider cross-slip and the dislocation glide on higher order crystallographic planes. The model is used to study both dislocation nucleation and propagation within several refractory MPEAs, and the results are compared with experimental work in the same alloys.
4:00 PM
Statistics of the NiCoCr Medium-entropy Alloy: Novel Aspect of an Old Puzzle: Zongrui Pei1; Rui Li2; G. Malcolm Stocks3; Michael Gao1; 1National Energy Technology Laboratory; 2University of Tennessee, Knoxville; 3Oak Ridge National Laboratory
We study the K-state phenomenon in the NiCoCr medium-entropy alloy using first-principles techniques jointly with the efficient Wang-Landau Monte-Carlo and simulated annealing algorithms. Our theoretical results successfully explain the existence of the peak around 940 K in the experimental specific heat curve that characterizes the K-state phenomenon and give a fine picture of its atomic origin. The peak is caused by the maximum change of the local configurations characterized by the short-range order (SRO) parameters at that temperature. Surprisingly, we find the Ni-Co pair distribution is not random even above the ordering transition temperature, dramatically different from Ni-Cr and Co-Cr, indicating the system cannot be treated as a pseudo binary alloy. This prototypical example shows the complicated nature of multicomponent alloys different from binary alloys. Our methods can be directly used to study the important K-state phenomenon observed in many other composition-concentrated alloys regardless of their number of components.
4:20 PM
Phase Stability of NbVZrMx (M = Ti, Mo; x = 0 – 1) Refractory Complex Concentrated Alloys: Zhaohan Zhang1; Mu Li1; Guodong Ren1; Arashdeep Thind1; Katharine Flores1; Rohan Mishra1; 1Washington University in St.Louis
Identifying dominant factors that lead to the stabilization of single-phase solid solutions, as opposed to multi-phases involving intermetallics, in complex concentrated alloys is a fundamental issue that remains unclear. In this work, we employ NbVZrTix and NbVZrMox as model systems to investigate the role of chemical composition on the phase-stability of refractory complex concentrated alloys and develop descriptors that govern their microstructure. We use a laser processing method to fabricate composition libraries of NbVZrMx (0<= x <=1). While the base alloy NbVZr exhibits a mixture of BCC solid solution with two Laves intermetallic phases, upon alloying with the fourth element, we observe suppression of the intermetallic phases and stabilization of BCC solid solutions in certain quaternary compositions. We will present results of first-principles density-functional-theory(DFT) calculations of various factors, including entropy, lattice distortions, electronic structure changes, and present key descriptors that govern the microstructure evolution, and consequently the mechanical properties.
4:40 PM
EAM and RF-MEAM Potentials for Thermal Properties of Zirconium Diboride: Bikash Timalsina1; Alin Niraula1; William Fahrenholtz2; Gregory Hilmas2; Andrew Duff3; Ridwan Sakidja1; 1Missouri State University; 2Missouri University of Science and Technology; 3Science and Technology Facilities Council
Reference free (RF) (M)EAM potentials have been developed to investigate the thermal properties of ultra-high temperature binary and entropy-stabilized diborides by fitting the DFT datasets including point defects, lattice deformations and high-temperature NPT and NVT ab-initio ensembles. The fitting technique implements a conjugate gradient minimizer along with the genetic algorithm using MEAMfit to fit the DFT datasets. Several materials properties including bulk modulus, elastic constants, cohesive and point defect energy are calculated and compared with the experimental and DFT results. In addition, the phonon dispersion and density of states were modeled to explain the experimental findings on the thermal expansion and phonon thermal conductivity of at ultra-high temperatures. The support from CMMI Division of NSF (Award No. 1902069) is gratefully acknowledged.