Advances in Multi-Principal Element Alloys II: Structures and Modeling
Sponsored by: TMS Structural Materials Division, TMS Functional Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Alloy Phases Committee
Program Organizers: Peter Liaw, University of Tennessee; Michael Gao, National Energy Technology Laboratory; E-Wen Huang, National Yang Ming Chiao Tung University; Jennifer Carter, Case Western Reserve University; Srivatsan Tirumalai; Xie Xie, FCA US LLC; James Brechtl, Oak Ridge National Laboratory; Gongyao Wang, Globus Medical
Wednesday 2:00 PM
March 22, 2023
Room: Aqua D
Location: Hilton
Session Chair: Chelsey Hargather, New Mexico Institute of Mining and Technology; Ying Yang, Oak Ridge National Laboratory
2:00 PM Invited
Interface-related Deformation Phenomena in High Entropy Alloy / Metallic Glass Nanolaminates: Jurgen Eckert1; Qi Xu1; Daniel Sopu1; Xudong Yuan1; Daniel Kiener2; 1Erich Schmid Institute of Materials Science; 2Montanuniversitaet Leoben, Dept. Materials Science
The deformation behavior of FeCoCrNiAl0.5 high entropy alloy (HEA) / FeCoCrNiAl1.7 metallic glass (MG) nanolaminates is explored through molecular dynamics simulations. Quantitative analysis of atomic strain and dislocation dynamics among competing and cooperative deformation mechanisms is accomplished upon uniaxial tensile deformation. The combination of crystalline and glassy nanolayers biases plastic deformation to regions near the crystalline-glass interface at lower strains, which lowers the activation barrier for dislocation nucleation and propagation. With increasing applied strain, dislocations are absorbed into the glass via slip transfer across the interface, triggering homogeneously distributed shear transformation zones. The competitive deformation mechanisms suppress localized shear bands and increase the resistance to dislocation motion, promoting enhanced ductility. Hence, high strength HEA/MG laminates and their complex deformation behavior may overcome the typical strength-ductility trade-off, rendering them promising candidates for a variety of structural and functional applications.
2:20 PM Invited
Effects of Precipitate Size and Spacing on Deformation-induced fcc to bcc Phase Transformation: Eva Zarkadoula1; Ying Yang1; Albina Borisevich1; Easo George1; 1Oak Ridge National Laboratory
Molecular dynamics simulations were used to study deformation-induced face-centered cubic (fcc) to body-centered cubic (bcc) transformation during uniaxial compression of an 80Fe-20Ni (at%) alloy with and without precipitates. Our purpose was to better understand recent experimental results in an Fe-Ni-based medium-entropy alloy where certain precipitates were found to constrain the fcc to bcc transformation. We find that larger precipitates and smaller spacings between precipitates hinder the phase transformation by impeding relaxation of internal elastic strains. These results deconvolute the individual effects of precipitate size and spacing and help interpret the experimental results where only their combined effects could be measured. Work supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Science and Engineering Division.
2:40 PM Invited
The Complexity of High Entropy Alloys: Huseyin Sehitoglu1; ASK Mohammed1; O. Celebi1; 1University of Illinois
A key development in analysis of dislocation motion in high entropy alloys is needed as negative stacking fault energy values have been obtained in atomistic simulations for many compositions. Standard formulas for determining the stacking fault width and dislocation core widths will fail under these circumstances. The talk will explain how to analyze negative stacking fault energy value effects and the partial dislocation spacing determination via an energy formulation. The model incorporates anisotropic elastic energies and the misfit energies and predicts frustrated motion of dislocation partials and their core widths. The results are significant in assessing new high entropy alloy compositions for CRSS (Critical Resolved Shear Stress) determination which is a key quantity in assessing fatigue of these class of alloys.
3:00 PM Invited
Diffusion-activation Energy in CoCrNi, CoCrFeNiMn, and CoCrFeNiCu High-entropy Alloys from First-principles Calculations, with Comparison to Creep-activation Energy: Christopher Lafferty1; Peter Liaw2; Chelsey Hargather1; 1New Mexico Institute of Mining and Technology; 2University of Tennessee
High-entropy alloys (HEAs) are potential candidates for high-performance engineering material applications. Creep is permanent, time-dependent inelastic deformation under applied stress, and is often the failure mechanism for structural engineering alloys in service applications. Diffusion behavior is an important contribution to secondary creep behavior. In the present work, first-principles calculations are employed to analyze activation energy for diffusion in the CoCrFeNiMn and CoCrFeNiCu HEAs and their constituent ternary systems. Widom-type substitution techniques are used. The relationship between the creep-activation energy and diffusion-activation energy in well studied systems, such as CoCrNi, is explored. Special quasi-random structures (SQS) are employed, and complications related to the structural complexity and magnetism when using first-principles techniques are discussed. Results are compared to known literature where available, and the importance of the calculations for novel alloy design are discussed.
3:20 PM Break
3:40 PM Invited
A Physical Model for Accurate Prediction of Lattice Parameter beyond Vegard's Law: An Application in bcc Solid Solution Alloys: Christopher Tandoc1; Yong-Jie Hu1; 1Drexel University
Lattice parameter is a fundamental material feature important in any alloy design. Vegard’s Law is widely adopted to estimate lattice parameters for substitutional solid solution alloys but is often inaccurate by not accounting for interatomic charge transfer which can lead to considerable deviations in local atomic volumes from pure elemental values. Herein, we present a novel physical model to accurately predict the lattice parameter of bcc solid solution alloys by effectively capturing the interatomic charge transfer between dissimilar elements. The model is derived as a simple linear expression of the atomic bond lengths of binary B2 and single-element bcc structures to predict lattice parameters for arbitrary alloy compositions without the need for any fitting parameters or additional first-principles calculations. The model reliability is systemically validated with the lattice parameters predicted by first-principles calculations of special quasirandom structures (SQS) for various alloy compositions spanning from binary to multicomponent systems.
4:00 PM Invited
Sequential Deformation-induced Phase Transformations in a Fe-Cr-Co-Ni Medium-entropy Alloy Explains Its Mechanical Behavior: Ying Yang1; Weicheng Zhong1; Easo George1; 1Oak Ridge National Laboratory
Phase transformations have been used to control the mechanical behaviors in alloys. Deformation induced one-step martensite transformation have been commonly observed to enhance work hardening rate. In this work, a two-step sequence of deformation induced phase transformation is activated in a non-equiatomic Fe-Cr-Co-Ni alloy at 77 K. Significant nanotwinning occurs at 293 K, whereas a sequential phase transformation (fcc to hcp-martensite to bcc-martensite) occurs at 77 K. Such sequential transformation enables high and sustained work hardening. Density functional theory calculation was performed to examine the relative phase stability and to provide an insight of its effects on the phase transformation sequence. This work represents the first detailed experimental observation of two-step transformation in a solid solution high-/medium-entropy alloy, and provides a new phase transformation pathway for sustaining work hardening in alloys.
4:20 PM Invited
Study of Short-Range Orders in Al-Co-Cr-Fe-Ni High-Entropy Alloys and Their Effects on Thermodynamic Properties – Atomistic Simulations and Data Analytics: Seungha Shin1; Md Abdullah Al Hasan1; Peter Liaw1; Dustin Gilbert1; 1University of Tennessee
Short-range order (SRO) in high entropy alloys (HEAs) has been observed, but more studies are needed for comprehensive understanding of SROs and their effects on the material properties. In this work, we characterized the SROs of AlxCrCoFeNi HEAs with different atomic configurations using the Warren-Cowley parameter and calculated structural, mechanical and thermodynamic properties using the molecular dynamics and density functional theory. Modern data analytics, such as the correlation analysis and machine learning algorithms, were employed to find correlations of the SRO with the HEA properties (e.g., bulk modulus, thermal expansion coefficient, and lattice thermal conductivity) and to predict the properties using the SRO and machine learning. In this talk, the difference of SROs between two different phases of AlxCrCoFeNi (i.e., FCC and BCC) and the machine-learning predictions of the HEA properties will be presented. This study is expected to contribute to the effective design of HEAs with desired properties.
4:40 PM Invited
Understanding the Short-range Ordering and Dislocation Behavior in BCC Refractory High Entropy Alloys: Shuai Chen1; Zachary Aitken1; Subrahmanyam Pattamatta2; Zhaoxuan Wu2; Zhi-Gen Yu1; David Srolovitz3; Peter Liaw4; Yong-Wei Zhang1; 1Institute of High Performance Computing; 2City University of Hong Kong; 3Hong Kong University; 4University of Tennessee
Despite intense research efforts, the fundamental mechanisms behind some remarkable phenomena of dislocations in BCC refractory high entropy alloys (RHEAs) remain unclear. Here, we investigate the underlying driving force for the short-range ordering (SRO) in a BCC MoTaTiWZr RHEA containing grain boundaries and the effects of SRO on the dislocation nucleation and propagation and resulting mechanical properties using a combination of the Monte Carlo method, molecular dynamic simulation, and density-functional theory calculation. Our results show that this RHEA is energetically favorable to undergo SRO driven the disparity and exclusivity of chemical affinity of its constituent elements. It is found that SROs enhance the energy barriers for both edge and screw dislocation motions and make the mobility of edge dislocations comparable to or even lower than screw dislocations, contributing to the unique dominance of edge dislocations in the BCC RHEA.
5:00 PM Invited
First-principles Study of the Phase Stability and Secondary Phase Formation in the AlxCoCrFeNi High-entropy Alloys: Chin-Lung Kuo1; 1National Taiwan University
We employed first-principles calculations to investigate the phase stability and secondary phase formation in the AlxCoCrFeNi HEA. Our calculations first revealed that the AlxCoCrFeNi HEA preferred to stay in A1 rather than in A2 structure as it was in a random-solid-solution configuration even with a Al content greater than x=2.0. As the Al content reached x=0.3, Ni3Al(L12) was favored to precipitate from the FCC matrix, where the Cr atoms were homogeneously distributed in the HEA lattice. As the Al content was increased up more than x=0.5, however, NiAl(B2)+FeCo(B2) precipitates started to become energetically more favorable than Ni3Al(L12) with the surrounding BCC Cr segregated out from the HEA matrix. Our calculations further revealed that the short-ranged order of Cr can play a critical role in determining the preferred secondary phase formation in the AlxCoCrFeNi HEA, which may also have strong influence on the nucleation paths of sigma phase at elevated temperatures.
5:20 PM
Numerical and Experimental Exploration of CCAs from the CrFeNiMoTi System for the Development of Cobalt-free Hardfacing Coatings: Clément Vary1; Pascal Aubry1; Ivan Guillot2; 1CEA; 2CNRS
This work’s purpose is to propose viable substitutes to the cobalt-based Stellite alloys, commonly used as wear-resistant coatings. Investigations revolve around Complex Concentrated Alloys (CCAs) from the CrFeNiMoTi system, for the coating of stainless steel pieces that need lasting protection from dry-sliding contact sollicitations. Previous work evidenced the (CrFeNi)90Mo5Ti5 alloy as a promising base, which mostly relies on the formation of a sigma phase within an FCC matrix for an increased hardness and an improved tribological behaviour. In this particular framework, the in situ alloying capabilities of the DED (Direct Energy Deposition) process were used for further explorations around this composition. This additive manufacturing technique is perfectly adapted to tackle the two main challenges: making directly functioning coatings and implementing rapid-screening strategies to broadly explore multi-principal elements systems. Coupled with a high-throughput use of the CALPHAD method, this combinatorial strategy speeds up material development compared to the more conventional ways.