High Entropy Alloys VIII: Thermal and Other Properties
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
Thursday 2:00 PM
February 27, 2020
Room: Marina Ballroom E
Location: Marriott Marquis Hotel
Session Chair: Jianxun Hu, Honda Development & Manufacturing of Americas
2:00 PM Invited
Development and Application of Phase-based Data Repository via CALPHAD Method in the HEA Discovery: Chuan Zhang1; Rui Feng2; Song-Mao Liang3; Michael Gao4; Fan Zhang1; Peter Liaw2; Shuanglin Chen1; 1CompuTherm LLC; 2University of Tennessee; 3University of Wisconsin-Madison; 4National Energy Technology Laboratory
The concept of high-entropy alloys (HEAs) opens a vast compositional space for potential alloys with promising properties. Since a successful structural material must simultaneously satisfy a demanding balance of over a dozen different properties, it is extremely challenging when use pure experimental investigations or traditional computational thermodynamics approach. In the present work, the phase-based data repository is developed for HEAs using the CALPHAD approach, which includes not only the thermochemical but also thermophysical information for various properties. We are then able to efficiently map different properties within the whole composition space of a system by coupling this phase-based data repository with the CALPHAD-based HTC tool, which enables the high-throughput design of high-performance HEAs with object-oriented design strategies.
2:20 PM Invited
Dislocation Dynamics in a BCC Refractory Multi-Principal Element Alloy MoNbTi: Fulin Wang1; Glenn Balbus1; Jungho Shin1; Paul Rottmann1; Jean-Charles Stinville1; Leah Mills1; Oleg Senkov2; Tresa Pollock1; Daniel Gianola1; 1Materials Department, University of California, Santa Barbara; 2Air Force Research Laboratory, Materials and Manufacturing Directorate
Refractory multi-principal element (MPE) alloys have emerged as a promising class of materials for their potential in high temperature applications. However, knowledge of the fundamental deformation mechanisms in the concentrated compositional environment and in the BCC crystal structure is still nascent, particularly on the experimental front. In this work, the dislocation behavior of a model alloy MoNbTi is studied by performing in situ tension experiments utilizing transmission mode in a scanning electron microscope (TSEM). Both collective slip activities and individual dislocation line morphologies are revealed. Quantitative crystallographic analyses allow the determination of the slip planes and the line directions of the gliding dislocations, and determination of the adherence to Schmid behavior. In contrast to common elemental BCC metals, the MPE alloy shows profuse slip activity on high order planes. The dislocations have mixed character, suggesting comparable critical resolved shear stress and mobility of the edge and screw components.
2:40 PM Invited
Comparison of High-throughput Experimental Results with Thermodynamic Calculations for more than 2000 HEAs: Chuangye Wang1; Sebastian Kube2; Jan Schroers2; Ji-Cheng Zhao1; 1University of Maryland; 2Yale University
Quinary high-entropy alloys (HEAs) of 2478 different compositions chosen from seven elements (Al, Cr, Mn, Fe, Co, Ni and Cu) were studied using high-throughput combinatorial thin film libraries. Large amounts of composition vs. crystal structure (phase) data were collected from the experimental survey. Thermodynamic calculations using Thermo-Calc and the associated HEA thermodynamic database were performed for these alloy compositions to predict the phases. The computed results were compared with experimental measurements. Both results show that HEAs prefer the bcc structure over the fcc structure with increasing atomic size difference. Detailed and comprehensive comparisons of experimental and computed results will be presented together with interesting conclusions.
3:00 PM Invited
Corrosion, Wear, and Surface Degradation Behavior of High Entropy Alloys: Mayur Pole1; Chaitanya Mahajan1; Maryam Sadeghilaridjani1; Sundeep Mukherjee1; 1University of North Texas
There is limited understanding of surface degradation mechanisms in high entropy alloys (HEAs) in terms of their corrosion, erosion, and wear behavior. There are few reports and limited understanding of the response of these alloys in different environments and as a function of temperature. We report on the corrosion and wear mechanisms for several single-phase and complex multi-principal high entropy alloys. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements were performed to understand the corrosion mechanisms. Wear behavior was evaluated for several HEAs as a function of temperature. The severity of corrosion and wear behavior changed with the test conditions. Raman and auger spectroscopy were employed to identify the surface degradation products and passivation layers. The good surface degradation resistance of HEAs makes them attractive for several structural applications in marine as well as elevated temperature environments.
3:20 PM Invited
High Entropy Alloy Effect on Stability of Potential Permanent Magnets: Ying Chen1; Arkapol Saengdeejing1; 1Tohoku University
Rare-earth element R involved compounds RFe 12 have been getting more attention since they are theoretically predicted to have high magnetization and magnetocrystalline anisotropy energy which are superior to Nd-Fe-B. However, the thermodynamic instability of RFe12 structure leads to a difficult in synthesis the bulk materials. The present work attempts to analysis the effect of random mixing of multi-element at both R and Fe sites of RFe12 to investigate the influence of the high entropy alloys on the stability of compounds based on various special quasirandom structure (SQS) models for (Sm, X)(Fe12 -xMx ) (X=Zr, Ce, M=1-, 2-, 3-, 4- 5- component of Ti, Co, Mo, Cr, Ni, V, Si). Gibbs free energies are calculated from electronic structures and various finite temperature effects. We found that combing the configurational entropy and vibrational entropy, the stabilities of the RFe12 -based compounds are obviously improved by multi-element random mixing.
3:40 PM Break
4:00 PM Invited
Speromagnetism and Asperomagnetism as the Ground States of the Tb-Dy-Ho-Er-Tm “Ideal” High-entropy Alloy: Janez Dolinsek1; 1Jožef Stefan Institute & University of Ljubljana
The Tb-Dy-Ho-Er-Tm hexagonal high-entropy alloy is a physical realization of an ideal solid solution with completely random mixing of the elements on a practically undistorted lattice. It represents a magnetically concentrated system with all lattice sites occupied by localized magnetic moments and containing randomness and frustration due to chemical disorder, thus sharing properties of an ordered crystal and an amorphous glass. The influence of this crystal-glass duality on the collective magnetic state was studied by the magnetization, magnetoresistance and specific heat experiments. The magnetic ground state is temperature-dependent, forming upon cooling first a speromagnetic state, then transforming into a spin glass state, followed by another transformation into an asperomagnetic state. The observed temperature evolution of the magnetic ground state is a result of temperature-dependent, competing magnetic interactions, where the distribution of the exchange interactions shifts continuously from the high-temperature speromagnetic-type through the spin glass-type to the low-temperature asperomagnetic-type.
4:20 PM Invited
Phase Stability in Refractory High Entropy Alloys: German Samolyuk1; Yuri Osetsky1; G. Malcolm Stocks1; James Morris2; 1Oak Ridge National Laboratory; 2Ames Laboratory
The configurational entropy associated with multiple components of nearly equiatomic composition give rise to the phrase “high entropy alloys,” and is clearly associated with the phase stability of observed single-phase materials. The expression for the ideal entropy of mixing, however, does not reflect the crystal structure. We present a density functional theoretical exploration of phase stability and competing crystal structures in medium and high entropy alloys formed of group IV and V elements. We find that a particular role of configurational disorder may determine the crystal structure, even at low temperatures where entropic considerations are minimal. Phase stability and other properties associated with the ground state structure are presented, across a number of alloy compositions. <BR><BR>This work is supposed by the Department of Energy’s Office of Science, through the Energy Dissipation to Defect Evolution EFRC (GDS, YO and GMS), and through the Materials Science and Engineering Division (JRM).
4:40 PM
Design of HEAs Strengthened by L12 Precipitates using High Throughput Thermodynamic Calculations: Thomas Rieger1; Jean-Marc Joubert1; Mathilde Laurent-Brocq1; Jean-Philippe Couzinié1; 1ICMPE, UMR 7182, CNRS - UPEC, F-94320, Thiais, France
High entropy alloys (HEAs) are considered as potential candidates for structural applications at high temperatures. Nevertheless, the mechanical behavior of the sole solid solution is not enough to withstand temperatures exceeding 800°C. Additional sources of strengthening are required before considering future applications.The most obvious way to strengthen fcc HEAs is to mimic nickel superalloys microstructure in which ordered precipitates are used to reinforce the disordered matrix with fcc structure. Accordingly, high throughput CALPHAD calculations are performed on the Ni-Co-Cr-Fe-Ti-Al senary system, allowing to map the entire composition space and to locate compositions with the desired fcc+L12 duplex microstructure. From these calculations, the role of each element on the microstructure is evaluated and an innovative method to represent the senary phase diagram is proposed. Five compositions of interest have been selected, synthesized and characterized. Good agreement between calculations and experimental results is observed.
5:00 PM
Quantifying the Effect of Randomness on Vacancy Diffusivity in High Entropy Alloys: Spencer Thomas1; Srikanth Patala1; 1North Carolina State University
Many virtues of High Entropy Alloys (HEAs), including their strength, ductility, and fatigue resistance, are highly sensitive to vacancy diffusivity. Similarly, solute interdiffusion is governed by vacancy diffusion – it is often unclear whether HEAs are truly stable, or effectively stabilized by slow interdiffusion. Efforts to tune the kinetic stability and the properties of HEAs depend on both the knowledge of the vacancy transition barriers within a given alloy and an understanding of how these barriers influence vacancy diffusivity. We present a generalized theory of vacancy diffusion in rugged energy landscapes, paired with Kinetic Monte Carlo simulations of HEA vacancy diffusion, driven by energy barrier statistics measured by nudged elastic band calculations of equiatomic CoNiCrFeMn. Theory and simulations show that vacancy diffusion in HEAs is not necessarily sluggish, but can potentially be tuned, and that trap models are an insufficient explanation for sluggish diffusion in the CoNiCrFeMn HEA.
5:20 PM Invited
High Temperature Phase Stability and Mechanical Behavior of Face-centered Cubic High Entropy Alloys: Min-Gu Jo1; Jin-Yoo Suh1; Jae-Hyeok Shim1; Heung Nam Han2; Woo-Sang Jung1; 1Korea Institute of Science and Technology; 2Seoul National University
To evaluate the availability of face-centered cubic (FCC) high entropy alloys for the high temperature structural applications, not only the mechanical properties but also phase stability at high temperature should be investigated. In this study, we studied a group of modified alloys of 5-component equi-molar alloy of CoCrFeMnNi, which is also known as Cantor alloy, by help of CALPHAD method varying melting temperature, width of FCC single phase region, and electronegativity difference to discuss the individual effect on high temperature applicability of the alloys. To check the phase and mechanical stability of the alloys at high temperature region, annealing experiment, high temperature tensile tests, and creep measurements were carried out at the temperature ranging from 823 to 1023 K. Detailed microstructural characterization including SEM-EBSD and TEM was carried out to discuss the microstructural development during prolonged high temperature exposure.