High Entropy Alloys VIII: Poster Session I
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

Tuesday 5:30 PM
February 25, 2020
Room: Sails Pavilion
Location: San Diego Convention Ctr


J-15 (Digital): Atomistic Modeling of Dislocations in a Random High-entropy Alloy: Diana Farkas1; Roberto Pasianot2; 1Virginia Polytechnic Institute; 2Atomic Energy Comission, Argentina
    The core structure and mobility of dissociated ½<110> dislocations in a model FCC high entropy alloy is studied using atomistic simulations. The simulations utilize model embedded-atom-method (EAM) potentials for al five component random equiatomic alloy, and a corresponding “average atom” potential. The dislocation line that corresponds to minimum energy in the random alloy is not straight but curvy and significant variations in dissociation distances are found. This effect is more significant for edge dislocations than for screw dislocations. Calculations also show that both the stable and unstable stacking fault energies vary according to the local composition of the alloy. A range of Peierls stresses cis found for the dislocations in the alloy, depending on the local composition. Most importantly, these stresses are significantly higher than in the pure components or those computed using an average atom potential. This effect is analyzed in terms of the core structure of the dislocations.

J-16 (Invited): Stability of the Stress-induced Phase in a TiZrHfNb0.3 Refractory High-entropy Alloy: Xuesong Fan1; Michael Gao2; Xiehang Chen3; Zongyang Lyu1; Yan Chen4; Ke An4; Eran Greenberg5; Vatali Prakapenka5; Qiaoshi Zeng3; Peter Liaw1; 1The University of Tennessee; 2National Energy Technology Laboratory; 3Center for High Pressure Science & Technology Advanced Research; 4Oak Ridge National Laboratory; 5Argonne National Laboratory
    High-entropy alloys (HEAs) with excellent structural properties have attracted extensive attentions in the recent decade. Body-centered-cubic (BCC) HEAs, especially those based on refractory elements, show stable microstructures and great mechanical properties at elevated temperatures, which could be widely used in high-temperature applications. Similar to TRIP (transformation-induced plasticity) steels, the stress-induced phase-transformation was also observed in the TiZrHfNbx refractory HEAs recently. This concept can improve the ductility, which supplies the deficiency of BCC alloys and broaden the application of refractory HEAs. To deeply understand the phase stability of the stress-induced phase in TiZrHfNbx alloys, in-situ neutron diffraction experiments at high temperatures and in-situ synchrotron X-ray diffraction experiments at high pressures were conducted on the pre-deformed TiZrHfNb0.3 HEA in this work. Coupled with several simulation and calculation methods, the concept will be further verified to benefit the design of refractory HEAs with excellent properties combining both the strength and ductility.

J-17: A Rapid Simulation Method of Single Phase High-entropy Alloys via CALPHAD-based High-throughput Calculation: Peiyong Chen1; Chanho Lee1; Xuesong Fan1; Chuan Zhang2; Jim Hu3; Peter Liaw1; 1University Of Tennessee; 2CompuTherm LLC; 3Honda R&D
    In the past decades, high-entropy alloys (HEAs) have drawn great attention due to their unique single-phase microstructures and outstanding mechanical properties as structural materials. Vast efforts have been devoted to finding single-phase HEAs from the aspect of experiments. However, targeting single-phase HEAs systems and compositions is still a challenge. In the present work, high throughput calculation method which is based on the calculation phase diagrams (CALPHADs) is performed to accelerate the pace of finding single-phase HEAs compositions computationally and investigating the HEAs systems in detail. A compositional mapping of the several HEAs system are conducted under certain criteria with different step sizes. In addition, these thermodynamics calculations will be discussed with the formation rules. Various of experiments are conducted for the verification of the single-phase prediction.

J-18: Ab Initio Modeling of Peierls Potential of Screw Dislocations in bcc High-entropy Alloys: Sheng Yin1; Jun Ding2; Mark Asta2; Robert Ritchie2; 1University of California, Berkeley; 2Lawrence Berkeley National Laboratory
    In traditional body-centered cubic metals, core properties of screw dislocations play critical role in plastic deformation at low temperature. Recently, much attention has been attracted to the refractory high-entropy alloys, which are also dominated by bcc microstructures. However, there has been relatively little study on screw dislocation properties or the short-range order effect in this new type of alloys. Here, using density functional theory, we investigate the cores structures in refractory HEAs and explore the height, shape and distribution of Peierls potentials. Furthermore, we showed the effect of different degrees of short-range order on the Peierls potentials of dislocations.

J-19: An Investigation into the Link Between Microstructure and Pitting Corrosion of Novel Alloy FBB8+Ti: Mark Wischhusen1; Carol Glover1; John Scully1; Peter Liaw2; Sean Agnew1; 1University of Virginia - Department of Materials Science and Engineering; 2University of Tennessee, Knoxville
    Compositionally and/or microstructurally complex alloys present new opportunities for optimizing properties beyond those of traditional alloys. Using a novel hierarchical microstructure design process, a new family of creep resistant ferritic alloys, denoted FBB8+Ti, has been developed which contains semi-coherent precipitates of Heusler (L21) and B2 intermetallic phases. The link between the microstructure and aqueous corrosion performance of these alloys is investigated by immersing samples in a 0.01 M NaCl solution under an applied potential, to determine the pitting and re-passivation potentials, in the as-cast and homogenized conditions. The phase content, microstructure, and pit-initiation sites are determined by a combination of x-ray diffraction and scanning electron microscopy. The corrosion behavior is observed to be insensitive to the Ti content. However, the pitting potentials and pit initiation sites are found to vary strongly with sample-surface preparation.

J-20: Anisotropic Lattice Distortion Induced by Hydrogen in CoCrFeMnNi High-entropy Alloy: Hung-Wei Yen1; Shi-Wei Chen2; Yu-Ting Mai1; Yi-Ting Lin1; 1National Taiwan University; 2National Synchrotron Radiation Research Center
    CoCrFeMnNi high-entropy alloy (HEA) owns high resistance to hydrogen embrittlement. This fact was explained by the enhancement of deformation twinning when hydrogen is involved. However, the relationship between mechanical twin and hydrogen in CoCrFeMnNi HEA is still absent. The current work investigated behavior of hydrogen in CoCrFeMnNi HEA by using thermal desorption analysis, synchronicity diffraction, and neutron scattering. It was found that stored hydrogen in CoCrFeMnNi HEA leads to anisotropic lattice strain on (1 1 1) plane. Stored hydrogen in the alloy is in the form of localized hydrogen clusters. This result conflicts the proposition claimed by W. Johnson since 1875. Moreover, this metallurgical principle can be developed into an approach to prevent from hydrogen embrittlement in advanced alloys.

J-21: Antiphase Boundaries in the B2 Matrix of the Al-Co-Cr-Fe-Ni High Entropy Alloy: Louisa Meshi1; Lior Natovitz1; Guy Hillel1; Yatir Linden1; Shai Salhov2; Malki Pinkas2; 1Ben Gurion University of the Negev; 2Nuclear Research Center Negev
    AlCoCrFeNi alloy solidifies in a dendritic regime with Al+Ni-rich dendrite (DR) and Fe+Cr-rich interdendrite (ID). Both areas are composed of ordered bcc (B2) matrix and bcc particles, displaying different morphology and hardness. We have found that the DR matrix contains ordered antiphase boundaries (APB). These AP domains arrest the growth of the bcc. In the ID area - short range order of the APBs was observed in the B2. There, bcc had characteristic Chinese letter-like (CL) morphology. Heat treatment at 850°C caused bcc->fcc+sigma transformation only in the ID; while DR remained essentially unchanged probably due to strain associated with the APB`s order. In our attempt to understand these phenomena, quaternary alloys, based on the quinary AlCoCrFeNi, were cast and characterized. CoCrFeNi and AlCoFeNi were single phase fcc and B2, respectively. AlCoCrFe exhibited fine CL bcc/B2 morphology with 720 HV hardness. AlCrFeNi and AlCoCrNi were similar to the quinary alloy.

J-22: Atomic Scale Modeling of Hydrogen Accommodation and Transport in BCC Refractory High Entropy Alloys: Simon Middleburgh1; Daniel King2; 1Nuclear Futures Institute; 2Imperial College London
    Experimentally, a number of high entropy alloys have been observed to be able to accommodate large amounts of hydrogen that can be readily retrieved through heating to specific release temperatures. The migration and release mechanisms of hydrogen in two classes of high entropy alloy: Hf-Nb-Ta-Ti-Zr and the other Nb-Ti-V-Zr, are investigated using temperature dependent density functional theory methods. Additionally, the influence of radiation damage on the quaternary composition is investigated using a combination of density functional theory and empirically based molecular dynamics techniques highlighting some key mechanisms elucidating the suitability of HEAs for use in nuclear applications (including water reactors, advanced coolants and fusion environments).

J-26: Corrosion Behavior of Selected High Entropy Alloys: Elzbieta Godlewska1; Marzena Mitoraj-Krolikowska1; Jakub Czerski1; Monika Jawanska1; Sergej Gein2; Ulrike Hecht2; 1AGH UST; 2Access e.V.
     AlCrNi(Co)Fe high entropy alloys with or without minor alloying additions, produced by either arc melting or by ingot metallurgy, were tested for corrosion resistance in different chemical environments comprising: sodium chloride at 3.5 wt.%, artificial sea water and 0.1 M sulfuric acid. The experiments were conducted mostly at room temperature and in some cases also at 50 oC, and in non-deaerated liquid media. Characterization of chemical behavior was based on immersion tests, OCV measurements, potentiodynamic measurements, impedance spectroscopy followed by post-exposure analysis involving visual inspection, SEM, EDS, XRD of the surface and ICP of the solutions being in contact with the samples. Overall behavior of the alloys was influenced by their exact chemical composition, distribution of phases and occurrence of physical defects on the surface.Investigations were conducted within NADEA project (M-ERA.NET 2017). Financial support from the National Science Centre Poland (UMO-2017/26/Z/ST8/01238) is gratefully acknowledged.

J-29: Deformation Mechanisms of Two Stable Face Centered Cubic High Entropy Alloys at Cryogenic Temperature: Feng He1; Shaolou Wei2; Zhijun Wang3; C. Cem Tasan2; 1City University of Hong Kong; 2Massachusetts Institute of Technology; 3 Northwestern Polytechnical University
     High strain hardening rate plays a key role in enabling face centered cubic (FCC) HEAs to have excellent ductility, high fracture toughness, and good ultimate tensile strength. Decreasing temperature usually further enhances the strain hardening capacity of FCC HEAs, resulting in enhanced tensile strength and ductility. However, the strain hardening mechanism of FCC HEAs at cryogenic temperature has not been fully understood. In the current work, we investigated the deformation mechanisms of two FCC HEAs with different stacking fault energies at cryogenic temperature. In-situ sychotron XRD tesnile test indicated that the stacking fault energy greatly affect strain hardening behaviors of FCC HEAs. Transimisson electron microscope (TEM) results demonstrated that it is dislocation slip mode, instead of deformation twining, that mainly affects the strain hardning capacities of the investigated two HEAs. The origins of this observation were systematically studied and will be presented in this talk.

J-30: Design of Non-equiatomic Refractory High Entropy Alloys through Combination of Various Strengthening Mechanisms Towards Strength-ductility Synergy: Cheng Zhang1; Benjamin MacDonald1; Fengwei Guo2; Yongwang Kang2; Xiaochang Xie2; Zhiqiang Fu1; Yizhang Zhou1; Enrique Lavernia1; 1Department of Materials Science and Engineering, University of California, Irvine; 2AECC Beijing Institute of Aeronautical Materials
    A novel non-equiatomic NbTaTi-based refractory high entropy alloy with reasonable density is introduced, which shows high strength at high temperature and good tensile ductility at room temperature through proper thermomechanical processing. The current alloy with BCC matrix is designed on the basis of the CALPHAD method. In the design process, apart from conventional solid-solution strengthening, some secondary phase for precipitation strengthening is introduced with the addition of Al and Si. Since Laves phases impair the ductility of refractory high entropy alloys, these phases are avoided in the current alloy design. Some elements that can absorb oxygen to form oxides are added, which can act as precipitates to strengthen the matrix and improve the oxidation resistance. Our results with this novel refractory high entropy alloy suggest that the proposed approach is promising for the design of novel refractory alloys.

J-31: Designing New Corrosion Resistant High Entropy Alloys with Exceptional Strength-ductility Synergy and Good Weldability: Saurabh Nene1; Sanya Gupta1; Rajiv Mishra1; 1University of North Texas
    Multiphase high entropy alloy (HEA) design provides abundant compositional space for developing newer materials having unexpected properties. However, good weldability is an important requirement for applications that require building a structural system. Thus we are pursuing new HEA design and processing approach wherein all other essential/desirable properties would be synergized with good weldability. As HEAs tend to limit solute partitioning or promote disordered solid solutions, a question emerges regarding formation of intermetallic compounds (IMCs) in the weld. Can IMCs be minimized in welds? With this notion, new metastable HEAs were designed and their preliminary weldability was evaluated through bead-on-plate friction stir welding (FSW). As-FSW HEAs showed exceptional combination of mechanical properties and corrosion resistance, the work was extended to dissimilar butt FSW of HEA/Al-7050 alloy. Initial results showed lower reactivity at the weld interface. The results are compared to dissimilar welds of Al alloy/stainless steel combinations.

J-32: Direct Production of High Entropy Alloy Powders: Jawad Haidar1; 1Kinaltek Pty Ltd.
    A novel method is presented for direct production of multi-component alloy powders using aluminothermic reduction of metal compounds based on V, Cr, Fe, Co, Ni, Cu, Zn, Nb, Mo, Rd, Ag, Sn, Ta and Al. The method provides for a mixture of precursor chemicals to be mixed and reacted exothermically with Al under controlled conditions using a control powder. Reduction is carried out in a controlled manner to regulate reaction rates and prevent excessive rise in the temperature of the reactants and the reaction products. Alloying additives such as C, O2, N2, B and Si can be included. Results are presented for direct production of high entropy alloys based on Co, Cr, Fe, Ni, Al and Nb.

J-34: Effect of Al on Microstructure, Hardness, and Corrosion Performance of Al-Cr-Fe-Mn Alloys: Jarrod Gesualdi1; Cameron Blanchard1; Hojong Kim1; 1The Pennsylvania State University
    Interfacial corrosion properties of as-cast Al-Cr-Fe-Mn alloys were studied under the control of Al content and microstructure by electrochemical polarization in aqueous solutions of Na2SO4 (1 M) and NaCl (1 M) at pH 3-7 and at room temperature. For example, the microstructure of Cr-Fe-Mn (10-67-23 at%) transformed from face-centered cubic (FCC) to body-centered cubic (BCC) structure with the addition of Al up to 15 at%. Based on anodic polarization curves, the increase of Al content resulted in the decrease of the passive current density (from 560 to 50 μA/cm2) and a positive shift of pitting potential, suggesting a beneficial effect of Al in enhancing corrosion resistance. In contrast, Vickers hardness values decreased at low Al content (5 at%) but increased with further Al addition (up to 15 at%), correlating with the change in microstructure.

J-35: Effect of Heat Treatment on the Microstructure and Mechanical Properties of AlCrFeNiCu High Entropy Alloy: Nicholus Malatji1; Rudolf Kanyane1; Thabo Lengopeng1; Patricia Popoola1; Sisa Pityana1; 1Tshwane University of Technology
    AlCrFeNiCu high entropy alloy was fabricated by laser metal deposition technique. The laser power was varied from 1600 to 2000 W while the scanning speed was kept constant at 1.2 m/min. The deposited alloys were then exposed to annealing heat treatment conditions at 700, 900 and 1100oC for 2 hours. The microstructural analysis showed that the alloy was characterized by dual phase structure (fcc + bcc) with the amount of bcc phase solution decreasing as the annealing temperature was increased. The exposure of the alloy to annealing conditions weakened its hardness properties and promoted grain growth.

J-36: Effect of Mn in CrCoFeNiMn High Entropy Alloy on Creep Performance: Kyle Rozman1; Martin Detrois1; Paul Jablonski1; Michael Gao1; Jeffrey Hawk1; 1National Energy Technology Laboratory
    Mechanical performance of equiatomic CoCrFeMnNi alloy is of considerable interest. Previously the authors presented their research on the creep performance equiatomic CrCoFeNiMn. Larson-Miller curves were reported similar to 300 series stainless steels. For this presentation creep performance of the high entropy alloy free of Mn is discussed and contrasted with the alloy with Mn. The subtraction of Mn lead to superior creep performance, however, anomalous strain rate behavior was observed in the Mn free alloy.

Cancelled
J-37: Electronic Properties and Characterization of Passive Films Formed on CrMnFeCoNi and CrFeCoNi Multiple Principal Element Alloys in a 0.1M NaOH Solution: Hamidreza Torbati-Sarraf1; Mitra Shabani1; Garrett Pataky1; Paul Jablonski1; Amir Poursaee1; 1Clemson University
     Passivation of CrMnFeCoNi and CrFeCoNi in 0.1 M NaOH solution were examined using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) tests. In-situ Raman spectroscopy was also exploited to characterize the composition of oxides formed at certain potentials. By sweeping potential from cathodic to anodic regions oxide films showed transitions from p to n and then n to p type semi conductive behavior. However, addition of Mn to CrFeCoNi changed flat band potential of the oxide film. Compositional analysis revealed that Mn depleted passive film form Cr compounds and reduced formation of higher valances of Co and Ni oxides. Cr, Mn and Fe spinel oxides dominated the oxide composition.Keywords: High entropy alloys, passivation, cyclic voltammetry, electrochemical impedance spectroscopy, Mott-Schottky, Raman spectroscopy, semi-conductive

J-38: Engineering Atomic-level Complexity in Complex Concentrated Alloys: Hyunseok Oh1; Khorgolkhuu Odbadrakh2; Sang Jun Kim3; Wook Ha Ryu3; Kook Noh Yoon3; Sai Mu4; Fritz Körmann5; Yuji Ikeda5; Cemal Cem Tasan1; Dierk Raabe5; Takeshi Egami4; Eun Soo Park3; 1Massachusetts Institute of Technology; 2University of Tennessee and Oak Ridge National Laboratory; 3Seoul National University; 4Oak Ridge National Laboratory; 5Max-Planck-Institut für Eisenforschung
    Quantitative and well targeted design of complex concentrated alloys (CCAs) is extremely challenging due to their immense compositional space. Here we show that the atomic-level pressure in single phase face-centered cubic (fcc) CCAs consisting of 3d transition metal elements (V, Cr, Mn, Fe, Co, and Ni) (3d CCAs) originates from the charge transfer between neighboring elements by theory (quantum-mechanically derived approximation) and experiment (element-dependent lattice distortion). It allows identifying the best suited element mix for massive solid solutions and predicting the resulting solid-solution strength using the simple electronegativity difference among the constituent elements. The method can be used to design new alloys with customized properties, such as a simple binary NiV solid solution which exceeds the yield strength of the established Cantor high entropy alloy by nearly a factor of 2, and TWIP or TRIP high entropy alloys having increased strain hardening rates while maintaining the similar yield strengths.

J-39: Enhanced Irradiation Resistance Through Phase Transformation in NiFeCoCrCu HEA Film: Li Jiang1; Yuan Xiu1; Wen Zhang1; Min Wang1; 1University of Michigan
    Nanocrystalline high entropy alloy (HEA) film with the composition of NiFeCoCrCu was irradiated by 3 MeV Ni ions to fluences of 4.7 × 1014, 2.8 × 1015, 1.5 × 1016, 8.0 × 1016 and 2.4 × 1017 cm-2 respectively, reaching a peak dose over 600 dpa. Microstructure analysis results reveal that a high density of nanotwins with an average thickness of 1.1 nm exist in the as-deposited film. After irradiation, FCC phase partially transforms into BCC phase, and no obvious radiation damage can be observed. Besides the large amount of grain boundaries in the HEA film, the phase boundaries also serve to effectively alleviate radiation damage by acting as defect sinks. Over all, our results not only present a promising candidate for nuclear material, but also provide science-based design and optimization of radiation-tolerant HEAs by introducing high-density nano-sized phase transformation.

J-40: Evaluation of Microstructural and Mechanical Properties of AlxCrFeMnNi High Entropy Alloys: Nicholus Malatji1; Khumo Masemola1; Patricia Popoola1; 1Tshwane University of Technology
    The microstructure and mechanical properties of arc melted and cast AlxCrFeMnNi high entropy alloys were investigated. The aluminium content was varied from 10 – 20 at% and homogenized at 1000oC for 2 hours. The microstructure of the alloys was characterized mainly by bcc phase structure with fcc precipitates. The increase in content of aluminium reduced the formation of fcc phase in the alloy. The compressive strength tests showed an improvement in strength as the aluminium content was increased but compromised the ductility of the alloys.

J-41: Evolution of Texture during Thermo-mechanical Processing of High Entropy Alloy (HEA): Shi Hoon Choi1; Min-seong Kim1; Lalit Kaushik1; Jaiveer Singh1; 1Sunchon National University
    In the present study, a high entropy alloy (HEA) of equiatomic CrMnFeCoNi was processed by vacuum induction melting followed by cold rolling. In order to break down the coarse cast structure, the homogenized specimens at 1,200° for 48 hrs were subsequently cold-rolled to ~80% reduction in thickness to a thickness of ~5 mm. These fully annealed specimens with thickness ~5 mm were used as the starting materials for subsequent ESAR (equal speed asymmetric rolling) processing up to 80% reduction in thickness to a final thickness of ~1mm and isochronally annealed for 1 hr at temperatures ranging from 800°C to 1,100°C. This was done to investigate the evolution of microstructure and partial recrystallization kinetics during thermo-mechanical processing of HEA. The annealing twin boundary fraction increased with increasing annealed grain size. The electron channeling contrast imaging (ECCI) was used for direct observation of stacking faults and dislocations at different strain levels.

J-43: Friction Stir Processing: A Microstructural Modification Technique for Complex Concentrated Alloys: Anumat Sittiho1; Jadzia Graves1; Madhumanti Bhattacharyya1; Indrajit Charit1; Rajiv Mishra2; 1University of Idaho; 2University of North Texas
    Complex concentrated alloys (CCAs) are a generic term used for a large group of metallic alloys containing multiple principal elements. More well known high entropy alloys (HEAs) are a subset of CCAs. CCAs often contain multi-phase microstructures with unique properties such as high strength-ductility combination, corrosion/oxidation resistance and wear resistance among others. In this work, friction stir processing (FSP) was applied to a CCA (Fe42Mn28Co10Cr15Si5) to study its transformation-induced plasticity (TRIP) characteristics. Microstructures of base metal (BM) and stir zone (SZ) were examined by optical microscopy, scanning electron microscopy and transmission electron microscopy. Mechanical properties of the BM and SZ of the CCA were evaluated using Vickers microhardness testing. FSP was found to increase microhardness from 231 to 273 HV0.5, because of the refined grain size and formation of more HCP-based second phases through a stress-induced transformation within the SZ.

J-44: Grain Size Dependent Entropy-driven Phase Transformation in High Entropy Oxides: Alexander Dupuy1; Xin Wang1; Julie Schoenung1; 1University of California, Irvine
    High entropy oxide (HEO) materials contain at least five oxide components, which form a single phase that is stabilized through configurational entropy. A unique characteristic of HEO materials is their reversible entropy-driven phase transformation. This feature presents an opportunity to produce oxide materials with highly controlled phase states. Here we explore the impact of grain size on the entropic phase transition in (CoCuMgNiZn)O ceramics. Sourced nanopowders are mixed using planetary ball milling. These powders are simultaneously reacted and densified using free sintering and spark plasma sintering (SPS). By leveraging these processing routes, we show that it is possible to produce fully dense HEO ceramics with grain sizes spanning several orders of magnitude. Characterization of these ceramics reveals that the phase transformation in the nanocrystalline samples begins 200°C lower than the coarse-grained samples. Additionally, the morphology of the secondary phase is strongly influenced by the grain size of the HEO samples.

J-45: Impact of Interstitial Alloying on Stacking-fault Energies in High-entropy Alloys from First Principles: Yuji Ikeda1; Jörg Neugebauer1; Fritz Körmann1; 1Max-Planck-Institut für Eisenforschung GmbH
    High-entropy alloys (HEAs) show remarkable mechanical properties. Stacking-fault energies (SFEs) have been successfully used as a descriptor to link atomic simulations to the macroscopic deformation mechanisms that are behind the superior mechanical performance to atomistic simulations. We study interstitial alloying in 3d-transition-element-based HEAs and its impact on SFEs using first-principles calculations. For face-centered cubic (FCC) CrMnFeCoNi, C is found to increase the SFE, while even qualitatively different trends are found for other HEAs. This demonstrates the possibility to tune the SFEs of HEAs by interstitial alloying. The C solution energies in FCC CrMnFeCoNi strongly vary depending on the specific local chemical environment of the C atoms. This also emphasizes the strong potential impact of chemical short-range order on interstitially alloyed HEAs.

J-46: Interdiffusion, Solubility Limit and Role of Enthalpy and Entropy in Senary FCC Al-Co-Cr-Fe-Ni-Mn High Entropy Alloy: Abhishek Mehta1; Yongho Sohn1; 1University of Central Florida
    High entropy and sluggish diffusion “core” effects were investigated in FCC Al-Co-Cr-Fe-Ni-Mn alloy by examining the off-equiatomic compositions, generated by the concentration profiles within solid-to-solid diffusion couples between β-Al48Ni52 and Co20Cr20Fe20Ni20Mn20 alloys in temperature range from 900 to 1200°C. Phase constituents, microstructure and concentration profiles were examined by X-ray diffraction and scanning electron microscopy. The magnitude of average effective interdiffusion coefficients of individual components in Al-Co-Cr-Fe-Ni-Mn alloys were compared to the interdiffusion coefficients in relevant ternary, quaternary, and quinary alloys. Solubility limit of Al in off-equiatomic Al-Co-Cr-Fe-Ni-Mn alloys was compared to the solubility limit of Al in equiatomic AlxCoCrFeNiMn determined using calculated equilibrium pseudo-binary phase diagram. Formation of single-phase in Al-Co-Cr-Fe-Ni-Mn senary HEAs was limited by the solubility limit of Al rather than absolute magnitude of configurational entropy. Findings from this study are discussed in terms of thermodynamic and kinetic contributions towards the stability of HEAs.

J-47: Internal Oxidation of Refractory MoWTaTiZr HEA Using Periodic DFT and Atomistic Thermodynamic Modeling: Eric Osei-Agyemang1; Ganesh Balasubramanian1; 1Lehigh University
     High-temperature strength, toughness and oxidation resistance are exhibited by Ni-based superalloys. However, increasing the application temperatures for such alloys become problematic due to melting temperatures of around 1350oC. New class of materials that can withstand harsher conditions at elevated temperatures are therefore desirable. High entropy alloys (HEA) based on refractory elements may achieve higher temperature operations with superior creep strength. Recently, a refractory Mo-W-Ta-Ti-Zr HEA was observed to exhibit greatly enhanced modulus of elasticity (3x at 300K) over near atomic cases and with higher moduli above 500K over commercial alloys (2.3x at 2000K). In this study, the internal oxidation mechanisms in the Mo-W-Ta-Ti-Zr HEA is analyzed. In a previous study, the surface oxidation mechanism was studied. Further analysis into the internal oxidation mechanism provides a complete picture and understandingon the usability of the Mo-W-Ta-Ti-Zr refractory HEA under oxidizing and corrosive environments

J-48: Low Cycle Fatigue Behavior and Cyclic Plastic Response of Equiatomic CrCoNi Medium-entropy Alloy with Partially and Fully Recrystallized Microstructures: Milan Heczko1; Connor Slone2; Veronika Mazanova1; Ivo Kubena1; Easo George3; Tomas Kruml1; Jaroslav Polak1; Michael Mills2; 1Institute of Physics of Materials CAS; 2The Ohio State University; 3Oak Ridge National Laboratory
    Equiatomic CrCoNi medium-entropy alloy was cold-rolled and heat-treated to produce partially and fully recrystallized microstructures. Alloys with these two different microstructural states were subjected to total strain controlled low cycle fatigue tests at room temperature over a wide range of strain amplitudes. Fatigue hardening/softening curves, cyclic stress-strain curves and fatigue life curves were evaluated. Simultaneously, the hysteresis loops during cyclic loading were analyzed using a generalized statistical theory. The probability density distribution function of the internal critical stresses, the effective saturated stress, and their evolution during cycling were derived for various strain amplitudes. The internal structure and the surface relief were studied and correlated with the cyclic response and the evolution of the probability density function of the internal critical stresses. The effect of partially and fully recrystallized microstructures on the low cycle fatigue behavior of the equiatomic CrCoNi medium-entropy alloy is also discussed.

J-49: Mechanical Properties and Tribocorrosion Behaviors of TiNbTaZr-based High-entropy Alloys for Biomedical Applications: Shih-Chieh Chao1; Kuan-Cheng Lai1; Po-Yu Chen1; 1National Tsing Hua University
    Conventional CoCrMo and Ti6Al4V alloys have been used as metallic biomaterials. However, metal ions released from CoCrMo alloy caused cytotoxicity and Ti6Al4V alloy had insufficient wear resistance. In order to integrate biocompatibility characteristics with unique properties of high-entropy alloys, such as high strength, outstanding structural stability and excellent corrosion and wear resistance, we synthesized MoNbTaTiZr and MoNbTaTiZrV HEAs by arc-melting for biomedical applications. The CALPHAD calculations revealed that the as-casted equiatomic MoNbTaTiZr and MoNbTaTiZrV HEAs possessed dual bcc phases confirmed by X-ray diffraction (XRD). Electron probe X-ray microanalysis (EPMA) results showed that tantalum, molybdenum and niobium were concentrated in dendritic arms while titanium and zirconium were enriched in interdendrite regions. Nanoindentation results showed that MoNbTaTiZr HEAs possessed hardness of 7.10.8 GPa and reduced modulus of 137.112.0 GPa. Biocompatibility, Wear resistance, tribocorrosion behaviors and metal ions released in PBS solution of HEAs are investigated and compared to commercial implants.

J-50: Mechanical Properties of CoCrFeMnNiMox High Entropy Alloy Films: Tzu-Hsuan Huang1; Chia-Lin Li1; Chun-Hway Hsueh1; 1National Taiwan University
    The multicomponent high entropy alloy films (HEAFs), CoCrFeMnNiMox (x=0, 0.05, 0.25, 0.5, 0.85), were prepared by co-sputtering of CoCrFeMnNi alloy and Mo targets. The content of Mo was controlled by the power applied on the Mo target. The effects of Mo addition on the crystal structure and hardness were investigated using X-ray diffraction and nanoindentation, respectively. The HEAFs exhibited a single FCC phase at lower Mo contents and eventually transformed to an amorphous structure with the increasing Mo content. The hardness increased from 6.53 GPa at x=0 to 8.77 GPa at x=0.85. However, the reduced modulus had a lowest value of 136 GPa at x=0.5. The strength and ductility of films were studied using micropillar compression tests.

J-51: Micro- and Mesoscale Mechanical Properties of a FeCrMnNi High Entropy Alloy Subject to Large Strain Extrusion Machining: Jonathan Gigax1; Osman El-Atwani1; Quinn McCulloch1; Berk Aytuna2; Mert Efe2; Saryu Fensin1; Stuart Maloy1; Nan Li1; 1Los Alamos National Lab; 2Middle East Technical University
    A recently developed bulk scale severe plastic deformation technique, large strain extrusion machining (LSEM), has been previous used to produce a fine-grained structure in steels and in pure W. The major advantage of the technique is its relative simplicity compared to traditional severe plastic deformation processes (i.e. high pressure torsion, equal channel angular extrusion). In this study, we subject an equiatomic FeCrMnNi high entropy alloy with a mixed face center cubic and body center cubic microstructure to various LSEM conditions. The microstructure was observed to have nanocrystalline grains in all conditions, with some more homogeneous than others. Nanoindentation showed a considerable increase in hardness for all LSEM conditions with respect to the base material. Mesoscale tensile testing revealed that while the tensile strength of the LSEM specimens was higher than that of the base material, the ductility was reduced significantly.

J-53: Microstructure Evolution and Mechanical Behavior of Nitrogen Interstitial CoCrFeMnNi High-entropy Alloys: Jing Zhang1; Min Seok Kim2; Kook Noh Yoon2; Heh Sang Ahn2; Eun Soo Park2; 1Jiangsu University of Science and Technology; 2Seoul National University
    A systematic study on the microstructure evolution and mechanical behavior at room temperature of interstitial CoCrFeMnNi high-entropy alloys (HEAs) with varying nitrogen contents is presented. After annealing,two distinct types of microstructure can be observed: fully recrystallized HEAs with 0.5, 1, 2 at.% nitrogen and partially recrystallized HEAs with 3 at.% nitrogen. There are threefold effects of nitrogen on the microstructure: i) reducing the size of recrystallized grains; ii) leading to a certain volume fraction of non-recrystallized zone; and iii) causing the formation of a higher volume fraction of nano-nitrides. Both the strength and ductility increase with 0.5 at.% and 1 at.% nitrogen, while yield and ultimate strengths increase accompanied by the decrease of elongation with higher nitrogen contents. However, the HEAs with 3 at.% nitrogen can still retain a good ductility (~30% elongation) with a significant strength improvement (yield strength by ~80% and ultimate strength by ~40%, respectively).

Cancelled
J-54: Multi-component Intermetallic Precipitation in FCC based Complex Concentrated Alloys: Sriswaroop Dasari1; Vishal Soni1; Abhinav Jagetia1; Rajarshi Banerjee1; 1University of North Texas
    Complex Concentrated Alloys (CCA’s) have the potential to couple concentrated solid solution matrix and intermetallic precipitation leading to both, precipitation strengthening as well as composite strengthening effects. Novel microstructures can be engineered in FCC based CCA’s by controlling the competition between L12 and B2/L21 phases. A wide range of mechanical properties can be obtained by tuning this competition via thermomechanical processing. FCC based CCAs have been designed using the CALPHAD approach to exploit this opportunity. The alloys were produced by conventional arc melting and thermo-mechanically processed to produce microstructures with different volume fractions of L12 and B2/L21 phases. Detailed microscopy using transmission electron microscopy (TEM) and atom probe tomography (APT) was carried out to characterize the alloy in various conditions. Mechanical properties of the conditions were characterized with room temperature tensile testing and microhardness.

J-55: Origin of High Cr Cation Fractions in Passive Oxide of Ni38Fe20CrxMn21-0.5xCo21-0.5x High Entropy Alloys: Junsoo Han1; Angela Gerard1; Xuejie Li2; James Saal3; Pin Lu3; Wolfgang Windl4; Kevin Ogle2; Gerald Frankel4; John Scully1; 1University of Virginia; 2Chimie ParisTech; 3Questek; 4The Ohio State University
     An important characteristic of the passive film of an alloy is which alloying elements are present in the oxide film and are responsible for the controlling passivity. Oxide enrichment models have been proposed derived from the relative dissolution rates of pure elements and the concentration of each element in the bulk alloy. In this work, the evolution of oxide cation fraction in the passive film on a high entropy alloy (Ni-Cr-Fe-Mn-Co) in a 0.1 M NaCl solution was compared to other alloys at the same Cr content. Cr enrichment was determined using X-ray photoelectron spectroscopy (XPS). To track the elemental dissolution in real time, atomic emission spectroelectrochemistry (AESEC) was applied, which directly measures the dissolution rate of each element during electrochemical tests. The fate of each element was tracked. Non-congruent low Cr dissolution rate coupled with preferential dissolution of other elements will be discussed.

J-56: Passivation Phenomena in Highly Corrosion Resistant High Entropy Alloys: An Evaluation of the Role of Chromium Content: Angela Gerard1; Junsoo Han1; Stephen McDonnell1; Dan Schreiber2; Pin Lu3; James Saal3; Wolfgang Windl4; Gerald Frankel4; John Scully1; 1University of Virginia; 2Pacific Northwest National Laboratory; 3Questek Innovations; 4Ohio State University
    Single phase multi-principle element alloys (MPEAs) with exceptional corrosion resistance in aqueous environments have been recently reported. A topic of great interest concerning MPEAs is the nature of the protective passive film and the key attributes that contribute to excellent corrosion resistance. Many oxide types have been reported for MPEAs, such as crystalline stoichiometric single cation oxides, complex non-stoichiometric oxides, and high entropy oxides. In this talk, the passivation behavior of several single phase Ni38Fe20CrxMn21-0.5xCo21-0.5x HEAs is reported over Cr concentrations ranging from 6 to 22 at.%. Passivation was investigated utilizing various in-situ electrochemical techniques as well as atomic emission spectro-electrochemistry. Ex-situ characterization of the oxide Cr cation fractions was determined using XPS and 3-D atom probe tomography. Findings were compared to Ni-Cr, Fe-Cr, and Co-Cr binary solid solution alloys over a similar range in Cr contents.

J-57: Phase Inversion in Refractory High Entropy Alloys: Vishal Soni1; Sriswaroop Dasari1; Bharat Gwalani1; Talukder Alam1; Oleg Senkov2; Daniel Miracle3; Rajarshi Banerjee1; 1University of North Texas; 2UES Inc.; 3Air Force Research Laboratory
    Refractory high entropy alloys (RHEAs) have been reported to exhibit higher strengths at elevated temperatures, as compared to conventional nickel base super alloys. Few of the Al-containing RHEAs exhibit an “inverted” superalloy-like microstructure where the ordered phase (B2) is the continuous matrix with discrete disordered BCC precipitates, unlike Ni-base superalloys where the disordered FCC phases is the continuous matrix along with L12 precipitates. The continuous B2 in these RHEAs are likely to be responsible for their poor room temperature ductility. The ductility of one such alloy, Al-0.5NbTa0.8Ti1.5V0.2Zr, was drastically improved by changing its microstructure from a “BCC precipitates in a B2 matrix”, to a “B2 precipitates in a BCC matrix” during isothermal annealing within the miscibility gap. In present study, this microstructural evolution during isothermal annealing has been investigated by coupling high-energy beam synchrotron experiments, transmission electron microscopy (TEM), and atom probe tomography (APT).

J-58: Phase Stability of B2-ordered High Entropy Alloy: Yonghua Meng1; Fenghui Duan1; Jie Pan1; Yi Li1; 1Shenyang National Laboratory for Materials Science, Institute of Metal Research
    The phase stability of B2 phase in the ZrTiHfCuNiFe HEA was investigated in comparison with that of the amorphous phase of the same composition. Annealed at 750-850 °C, the HEA casting rod and amorphous ribbon exhibit the same predominant B2 phase. While annealed at 600 °C and below even for prolonged annealing time 1000 h, no phase transformation is observed in the HEA casting rod with B2 phase, whereas multiple phases (i.e. (Cu,Ni)10(Zr,Hf)7, ordered HCP, B2 and FeTi) are formed in the amorphous ribbon. The B2 phase obtained by annealing amorphous ribbon at high temperature does remain its B2 structure when annealed at 600 °C again. These observations clearly indicate that B2 phase in the ZrTiHfCuNiFe HEA exhibits higher thermal stability at 600 °C and below compared with the amorphous phase of the same composition, which may be attributed to the low phase transformation temperature and coordinated long-range sluggish diffusion.

J-60: Second-phase of 29Fe15Al18Cr27Ni High Entropy Alloy: Jintao Wang1; Shouping Liu1; Xiong Xiao1; Xiaoyu Han1; 1Chongqing University
     In this study, FeNiAlCr high-entropy alloy was prepared by vacuum induction furnace which grain size is about 2-3 μm. There are two second-phases were found in the alloy: Geometric Close-Packed phase (GCP) and Topologically Close-Packed Phases (TCP). The GCP nanophase, Fe2AlCr, is distributed in the grain. The continuous TCP phase, Ni3Al phase (β phase), is formed at the grain boundary of the alloy.In this study, the formation and decomposition of the second phase in high-entropy alloys and the effect of the second phase on the properties and mechanism of the alloys are analyzed by SEM, EDS, XRD, DSC-TG, tensile test and resistivity test.

J-61: Size Effects and the Hall-Petch Relationship in the Mn17Fe22Co24Ni24Cu13 System: Artashes Ter-Isahakyan1; John Balk1; 1University of Kentucky
    The science and engineering of materials is, to an extent, expressed in terms of length scales and resultant interactions. The intrinsic nature of HEAs introduces an unexplored condition that is yet to be critically evaluated. To date, only a handful studies have explored grain boundary strengthening for HEA. In each case, extreme strengthening effects are reported. Some suggestions have been made which include higher friction stress due to lattice distortion, influences from dislocation curvature and dislocation glide mode. These may all be possible options; on the other hand, the physical interpretation of each constant within the Hall-Petch(HP) relation must be compatible with a model that accounts for such a contribution. In this work, the HP relation based on various models is evaluated through tensile testing, thermal analysis and work function measurements for a non-equiatomic Mn17Fe22Co24Ni24Cu13 HEA. Discussions aim to answer a fundamental question, “Do HEAs exhibit exceptional size effects?”.

J-62: Static and Dynamic Mechanical Performance of Non-equiatomic CoCrFeMnNi HEA: Kyle Rozman1; Paul Jablonski1; Jeffrey Hawk1; Michael Gao1; 1National Energy Technology Laboratory
    High entropy alloys (HEAs) are a new class of materials exploiting entropy of mixing to stabilize the microstructure. Equiatomic CoCrFeMnNi is of considerable interest. Mechanical performance of this alloy has low yield strength and strain hardens significantly. The question arises: Does an equiatomic formulation result in the best performance? This research focuses on a variant of CoCrFeMnNi with a lower proportion of Mn, ~5% atomic with the balance being equiatomic. Surprisingly, the lower Mn variant was predicted to have a higher entropy than the equiatomic alloy based on CALPHAD calculations. Static tensile behavior from room temperature to 800℃ is discussed. Additionally, room temperature high cycle fatigue tests were conducted, and results are discussed and compared with results of CoCrFeMnNi alloy where appropriate.

J-63: Strengthening of Transformation-induced Plasticity-assisted High Entropy Alloy via Interstitial Nitrogen: Kenta Yamanaka1; Manami Mori2; Yusuke Onuki3; Shigeo Sato3; Akihiko Chiba1; 1Tohoku University; 2National Institute of Technology, Sendai College; 3Ibaraki University
    Non-equimolar high-entropy alloys (HEAs) showing transformation-induced plasticity (TRIP) have a great potential as a novel class of materials with excellent mechanical properties. However, the yield strength of such alloys is generally low and needs to be improved. In this study, we examined the effect of interstitial nitrogen on the mechanical behavior of TRIP-assisted Co20Cr20Fe34Mn20Ni6 HEAs. The alloys showed single-phase fcc microstructures both in the hot-swaged and annealed states. The results of tensile testing indicated that adding trace nitrogen (0.08 mass%) significantly strengthens the alloys with maintaining good ductility. Notably, thanks to the interaction between dislocations and nitrogen atoms, the metastable parent phase of the N-doped HEA was effectively strengthened by introducing dislocations via hot deformation at the fcc stable temperatures. Accordingly, a superior strength-ductility combination was realized. The martensitic transformation kinetics and dislocation dynamics in the studied alloys under tensile loading were examined by in-situ neutron diffraction measurements.

J-64: Synthesis of High Entropy Metal Carbides by a Solvothermal Process: Ved Vakharia1; Olivia Graeve1; 1University of California, San Diego
    In recent years, high entropy ceramics (HECs) have been investigated for their superior strength, corrosion resistance, and high temperature stability. HECs can be defined as solid solutions composed of five or more principle elements in equimolar ratios, forming one single phase, and therefore consisting of a system of high entropy. We have implemented the solvothermal process to synthesize high entropy metal carbides (HEMCs), specifically (MoNbTaVW)C. En route to this HEMC, we have produced binary, ternary, quaternary, quinary, and senary metal carbides. Solid solutions of (NbTa)C and (NbTaW)C have been confirmed by a combination of X-ray diffraction and energy-dispersive spectroscopy. We are using Rietveld refinement to deconvolute the X-ray diffraction data and obtain approximate phase compositions in our compounds to optimize precursor amounts and obtain a solid solution. We are also investigating the importance of vanadium, as it can exist in different electronic states, helping to form the HEMC.

J-65: Tailoring Multi-principal Element (MPE) Alloy Compositions based on Competing Deformation Mechanisms: K V Vamsi1; Marie-Agathe Charpagne1; Anton Van der Ven1; Tresa Pollock1; 1University of California
    The potential compositional space for multi-principal element alloys is large, posing challenges for identification of promising new compositions. In this work, we propose a high-throughput framework to explore the FCC/HCP MPE composition space with respective to competing deformation mechanisms: slip and twinning. A “twinnability” criteria that is dependent on the relative magnitudes of stable and unstable stacking fault energies was deployed as a design parameter. Using Ni-Co-Ru as a model system, the synergistic effects of the relevant fault energies and their influence on twinnability have been investigated. Electronic structure calculations were performed to estimate the structural energies and bulk properties to predict propensity for twinning in ternary Ni-Co-Ru. Predicted behavior will be compared to experimental observations for selected compositions

Cancelled
J-66: The Controlled Large-area Synthesis of Two Dimensional Metals: Tianyu Wang1; Quanfeng He1; Jingyang Zhang1; Zhaoyi Ding1; Fucheng Li1; Yong Yang1; 1City University of Hong Kong
    The rise of nanotechnology has been propelled by low dimensional metals. Albeit the long perceived importance, synthesis of freestanding metallic nanomembranes, or the so-called 2D metals, however, has been restricted to simple metals with a very limited in-plane size (< 10 m). In this work, we developed a low-cost method to synthesize 2D metals through polymer surface buckling enabled exfoliation. The 2D metals so obtained could be as chemically complex as high entropy alloys while possessing in-plane dimensions at the scale of bulk metals (> 1 cm). With our approach, we successfully synthesized a variety of 2D metals, such as 2D high entropy alloy and 2D metallic glass, with controllable geometries and morphologies. Moreover, our approach can be readily extended to non-metals and composites, thereby opening a large window to the fabrication of a wide range of 2D materials of technologic importance, which however have never been reported before.

J-67: The Prediction of Enthalpy and Elastic Properties of Fe-Cr-Co-Ni High Entropy Alloys by Using First Principles Methods: Songge Yang1; Mohammad Asadikiya1; Vadym Drozd2; Yu Zhong1; 1Worcester Polytechnic Institute; 2Florida International University
    Equiatomic FeCrCoNi high entropy alloys (HEAs) have been studied extensively in the past decade, not only because of its special properties like high tensile ductility and fracture toughness but also because it is considered as a foundation system for the development of FeCrCoNi-based HEAs. In the project, the first principles calculations are proceeded to predict the elastic properties and enthalpy formations of fcc and bcc Fe-Cr-Co-Ni HEA single crystals by using special quasirandom structure (SQS) approach. The predictions will start with binaries of Fe-Cr-Co-Ni system and will be continued with ternaries and finally quaternary. After that, based on the calculation results from first principles, the CALPHAD-type descriptions for enthalpy and elastic moduli in Fe-Cr-Co-Ni system with full compositions range will be constructed.

J-68: Thermal Expansion of Refractory MoWTaTiZr High Entropy Alloy: Eric Osei-Agyemang1; Ganesh Balasubramanian1; 1Lehigh University
     Though Ni-based superalloys exhibit superior performance at moderate temperatures, the quest for new class of materials becomes desirable at elevated temperatures and extreme working conditions as the Ni-based superalloys have low melting temperatures. High entropy alloys (HEA) based on refractory elements may achieve higher temperature operations with superior creep strength. At elevated temperatures, Mo based HEAs have been observed to exhibit good thermal and mechanical properties. Recently, a refractory Mo-W-Ta-Ti-Zr HEA was observed to exhibit greatly enhanced modulus of elasticity (3x at 300K) over near atomic cases and with higher moduli above 500K over commercial alloys (2.3x at 2000K). The usability of the recently identified Mo-W-Ta-Ti-Zr HEA at extreme working conditions is required. In this study, a Quasi-Harmonic Approximation (QHA) method is used to estimate the coefficient of thermal expansion (CTE) for refractory Mo-W-Ta-Ti-Zr HEA. We discuss the effect of composition on the mechanical properties and associated thermally driven mechanisms.

J-70: Ultrastrong VCoNi Medium-entropy Alloy Enabled by Severe Lattice Distortion: Seok Su Sohn1; Alisson Kwiatkowski da Silva2; Yuji Ikeda2; Fritz Körmann2; Wenjun Lu2; Won Seok Choi3; Baptiste Gault2; Dirk Ponge2; Jörg Neugebauer2; Dierk Raabe2; 1Korea University; 2Max-Planck-Institut für Eisenforschung; 3Korea Advanced Institute of Science and Technology
    Severe lattice distortion is a core effect in the design of multiprincipal element alloys with the aim to enhance yield strength. Yet, the yield strength values of those alloys investigated so far do not substantially exceed those of conventional alloys due to the insufficient utilization of lattice distortion. In this study, for a VCoNi equiatomic solid solution alloy, it is demonstrated that a wide fluctuation of the atomic bond distances, i.e., severe lattice distortion, improves both yield stress and its sensitivity to grain size. The refined grain size of 1 um in an average leads to the yield strength of 1.3 GPa. we present that the degree of lattice distortion is indeed a key parameter in controlling strengthening mechanisms for the design of hitherto unexplored ultrastrong medium-entropy single-phase alloys.