High Entropy Alloys VIII: Poster Session 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

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

J-72: A Machine Learning Model for Alloy Design: Zhaohan Zhang1; Mu Li1; Katharine Flores1; Rohan Mishra1; 1Washington University in St.Louis
    Developing fast and accurate methods to promote alloy discovery is of practical interest, especially with the vast composition space offered by multi-principal element alloys (MPEAs). While density-functional-theory (DFT)-based methods have accelerated design of binary and ternary alloys, they are not amenable for rapidly screening the vast combinatorial space of MPEAs. We develop a machine-learning model for predicting the DFT-calculated formation enthalpy of alloys and use it to identify stable alloys. The model uses easily accessible elemental properties as descriptors and has a mean absolute error (MAE) of ∼ 6 meV/atom for binary alloys. We use the model to successfully identify new binary intermetallics that are subsequently confirmed using DFT and experiments. Model trained with binary intermetallics can predict formation enthalpy of ternary intermetallics with an MAE as good as DFT calculation. We further apply it to MPEAs to predict the formation of single-phase solid solutions with bcc and fcc structures.

J-73: A Strategy for Designing Heterogeneous Medium-entropy Alloys with Excellent Tensile Properties: Jongun Moon1; Jeong Min Park1; Jae Wung Bae1; Hyoung Seop Kim1; 1POSTECH
    Here, a new strategy for designing heterogeneous medium-entropy alloys with light-weight and excellent mechanical properties is proposed. Alx(CuFeMn)100-x (x = 0, 7.5, and 15 at%) alloys were developed by utilizing the immiscible nature of Cu-Fe alloys. The microstructures of the alloys show phase separation into Cu-rich and Fe-rich regions, and the addition of Al transforms the crystal structure from dual face-centered cubic to face-centered cubic and body-centered cubic. Phase separation of the microstructure into two domains enables further dissolution of Al into the matrix. The alloys exhibit high strength because of solid solution strengthening and hetero-deformation induced strengthening caused by heterogeneous microstructures. The presence of nano-scale twins and essential partially recrystallized microstructures also enhances the strength of the alloys. This new type of medium-entropy alloys is expected to expand the design window in physical metallurgy.

J-74: Ab Initio Modeling of Large Defects in γ, γ', and γ" Superalloys: Saro San1; Wai-Yim Ching1; 1University of Missouri, Kansas City
     Using first-principles methods based on density functional theory, we explore the structural, electronic and mechanical properties of 7 interface and defect-containing models on Ni-based alloys. The alloy phase of (Ni) and (Ni3Al) are solid solution on FCC lattice and (Ni3Nb) on BCT. The supercell for and models and supercell for with 864 atoms each is carefully constructed and fully relaxed. We investigate the interface between and of the three models of inclusion of in as precipitate with different volumes. By removing the included precipitate and then fully relax the models again, we obtain three models with specific voids of different porosity. The electronic structure, partial charge distribution, interatomic bonding and mechanical properties of these 7 models are calculated. The results show that the defect models are more ductile than the pure alloy system.

J-75: Analysis of Irradiation Resistance of Tungsten-based Reduced Activation Alloy for Fusion Plasma Applications: Owais Waseem1; Ho Jin Ryu1; 1KAIST, Korea
    The promising mechanical strength, sputtering resistance and thermal conductivity make tungsten (W) a potential candidate for future fusion plasma facing applications. However, the requirement of good combination of strength, toughness and irradiation resistance emphasize upon the requirement of innovative W-based materials. This paper presents development and analysis of a novel reduced activation W-based alloy WxTaTiVCr. We fabricated the samples by spark plasma sintering of mixture of pure elemental powders. Microstructural and mechanical properties have been analyzed via electron microscopy, compression and toughness tests, respectively. The samples were irradiated through proton irradiation, and surface morphology, sub-surface microstructure and nanoindentation hardness or irradiated and un-irradiated samples were analyzed. High voltage electron microscope (HVEM) was employed for in-situ analysis of resistance to electron irradiation. The enhanced irradiation resistance of WxTaTiVCr have been observed.

J-76: Analysis of Strengthening due to Grain Boundaries and Annealing Twin Boundaries in the CrCoNi Medium-entropy Alloy: Mike Schneider1; Easo George2; Tomš Zležk3; Antonn Dlouh3; Gunther Eggeler1; Guillaume Laplanche1; 1Ruhr-Universitaet Bochum; 2Oak Ridge National Laboratory; 3Institute of Physics of Materials
    The CrCoNi medium-entropy-alloy has the best combination of strength and ductility among all single-phase FCC subsets of the Cr-Mn-Fe-Co-Ni Cantor system. In this study the yield strength of CrCoNi was determined in compression as a function of grain size (3m-175m) and temperature (77K-873K). Grain size and texture analyses were performed using backscattered electron imaging and diffraction, respectively. The Hall-Petch slope is roughly temperature independent between 77K and 673K while grain boundary sliding plays a role for T>673K. Transmission electron microscopy of deformed specimens revealed the formation of pile-ups at grain and annealing twin boundaries indicating that both contribute to strength, also shown by 1D DDD simulations. Assuming that both types of boundaries have the same strength, the boundary strength calculated using a pile-up model from our experimental data corresponds roughly to the stress required to constrict Shockley partials, suggesting that dissociated dislocations must recombine before crossing the grain/annealing twin boundaries.

J-77: Atom Probe Tomography Study of a Fe25Ni25Co25Ti15Al10 High-entropy Alloy: Zhiqiang Fu1; Andrew Hoffman2; Benjamin MacDonald1; Maalavan Arivu2; Haiming Wen2; Enrique Lavernia1; 1University of California, Irvine; 2Missouri University of Science and Technology
    Transmission electron microscopy (TEM) and atom probe tomography (APT) were utilized to investigate the microstructure and phases in a Fe25Ni25Co25Ti15Al10 high-entropy alloy (HEA) prepared by powder metallurgy. The bulk HEA exhibits a microstructure composed of a minor bcc phase (17.7 vol.%), together with a primary fcc phase (82.3 vol.%) containing hierarchical nanoprecipitates. The bcc phase, was a B2-type NiAl phase, containing substantial amounts of Co, Ti and Fe. The fcc phase consisted of a γ Fe-(Co,Ni)-based solid-solution matrix (A1), and coherent primary γ’ (Ni,Co)3-(Ti,Al)-based intermetallic precipitates (L12). A1 structured secondary γ* precipitates were found coherently embedded within the L12-γ’ precipitates. In addition, a complex type of Al-Ti-O oxide as well as a (Ti,Ni)(C,N) was identified via APT. To validate these findings, the CALPHAD method was utilized with ThermoCalc’s newest HEA database to calculate the relative volume fraction and chemistry of possible equilibrium phases given the bulk composition and processing parameters.

J-78: Atomic Diffusion in Melts of Refractory HEAs: Ankit Roy1; Ganesh Balasubramanian1; 1Lehigh University
    The new class of alloys, High-entropy alloys (HEAs) show promising mechanical properties and have to be synthesized at ~ 3300 K due to high intrinsic melting points (MP) of constituent elements. Though solid state properties of HEAs have been well investigated, the dynamics of molten stage aren’t. Such a study can provide important insights about the chances formation of a single phase solid solution. In this work, we employ molecular dynamics (MD) simulations to study molten stage properties of refractory Mo-Ta-Ti-W-Zr HEA family at various temperatures well above theoretical MP (calculated by rule of mixtures). Self-diffusion coefficients have been obtained by using the velocity auto-correlation function (VACF) and mean-squared displacement (MSD) methods. Good agreement exist between values of self-diffusion coefficients obtained by these methods. Further, a structural pair correlation analysis (g (r)) reveals ordering and clustering tendencies which can answer the critical question- will single phase solid solution be formed?

J-79: CALPHAD Aided Design of MoNbTiZr-based High Entropy Alloys: Benjamin MacDonald1; Cheng Zhang1; Zhiqiang Fu1; Fengwei Guo2; Yongwang Kang2; Xiaochang Xie2; Yizhang Zhou1; Enrique Lavernia1; 1University of California, Irvine; 2AECC Beijing Institute of Aeronautical Materials
    CALPHAD calculations using the current high entropy database developed by ThermoCalc are first utilized to search compositional space for candidate alloy compositions that exhibit beneficial equilibrium phases for high temperature stability and properties. In addition to the base constituents MoNbTiZr, other alloying elements, including Al, are screened for increases to the stability of multiple body centered cubic solid solutions while avoiding the stabilization of phases deleterious to mechanical properties, particularly laves phases. To evaluate the CALPHAD predictions, candidate alloy compositions are synthesized via arc melting for microstructural characterization. As-cast and heat treated multi-phase microstructures are characterized through x-ray diffraction, energy dispersive spectroscopy, and high resolution transmission electron microscopy to identify present phases. To understand the strengthening role of each phase in these alloys, the mechanical behavior of the alloys is assessed in terms of tensile tests at room temperature and at elevated temperatures.

J-80: Composition Design of Coherent Precipitate-strengthening AlCuFeNiTi Multi-principal Element Alloys by High-throughput CALPHAD-type Calculation: Shao-Yu Yen1; Hao-che Wang1; Shih-kang Lin1; 1National Cheng-Kung University
    For decades, multi-principal element alloys (MPEAs), also known as complex concentrated alloys (CCAs) and high entropy alloys (HEAs), has been attracting widely research due to their outstanding mechanical properties such as specific strength and tensile yield strength. Due to the numerous element combinations and multi-dimensional composition space for MPEAs, conventional exploration with trial-and–error experiments to study MPEAs is very costly and time-consuming. With the assistance of computational thermodynamics, the period of new alloy design can be significantly reduced. In this work, high-throughput CALPHAD-type calculation is performed to roughly screen out the γ/γ' coherent precipitates-strengthening Al-Cu-Fe-Ni-Ti system in PanHEA database. Since the amount of precipitates has an influence on the strengthening effect, finer screening is then conducted to sort out the compositions with different phase fraction of L12(γ'). A series of experiments are carried out to verify the calculation results.

J-81: Compositional Effects of Stacking Fault Energies in Ni-based FCC Concentrated Alloys: Liubin Xu1; Luis Casillas-Trujillo2; Yanfei Gao1; Haixuan Xu1; 1The University of Tennessee, Knoxville; 2The University of Tennessee, Knoxville (now at Linkping University, Sweden)
    The stacking fault energy (SFE) is a crucial material property that is closely linked to dislocation and planar faults in face-centered cubic (fcc) materials. To understand the complex deformation mechanisms in concentrated alloys, such as medium/high entropy alloys, we investigate the SFEs in several Ni-based binary concentrated alloys (e.g. NiCo, NiCu, and NiFe) with fcc structure using both atomistic simulations and density functional theory (DFT) calculations. We have identified distinguished trends of SFEs vs. alloy compositions and the observed trends can’t be explained by simply extending the dilute-alloy model. To reveal the physical origin of these trends, data analysis toolkits are employed to correlate the SFEs with other fundamental materials properties. Electronic and magnetic contributions to the SFEs are discussed by comparing the atomistic simulations and DFT results. This research provides fundamental insights of compositional effects on mechanical properties of materials that was not included in conventional alloy theories.

J-82: Deformation Behavior of the Al0.3CoCrFeNi High-entropy Alloy during Low-cycle Fatigue by In-situ Neutron Diffraction: Zongyang Lyu1; Rui Feng1; Di Xie1; Yan Chen2; Ke An2; Yanfei Gao1; Peter Liaw1; 1The University of Tennessee; 2Spallation Neutron Source, Oak Ridge National Laboratory
    The in-situ neutron diffraction was conducted to investigate the deformation behavior of the Al0.3CoCrFeNi high-entropy alloy (HEA) with a face-centered-cubic (FCC) phase at ambient temperature. The wall spacing and density of dislocation are calculated based on the diffraction data, which are related to cyclic hardening. The lattice strain evolution, based on selected loading cycles, was plotted to demonstrate the deformation mechanism during cyclic loading. It will facilitate a better understanding on the mechanical behavior of high-entropy alloys with FCC crystal structures.

J-83: Deformation-induced Short-range Ordering and Its Impact on Cryogenic Deformation in Boron-doped High-Entropy Alloys: Jae Bok Seol1; Jae Wung Bae1; Zhiming Li2; Won-Seok Ko3; Hyoung Seop Kim1; 1POSTECH; 2Max-Planck-Institut fr Eisenforschung GmbH, Max-Planck-Strae; 3University of Ulsan
    We report a strategy for improving the cryogenic strength of FCC-structured HEAs through short-range order (SRO), which is driven by soluble boron at the high-entropy grain interiors, not by interfacial boron. Introducing soluble boron into the FCC matrices provided the key benefits, i.e., creation of SROs and increase in SRO degree during cryogenic-temperature deformation, as proved by TEM diffraction and synchrotron XRD. With this new approach, we increased the cryogenic yield strengths of non-equiatomic Fe40Mn40Co10Cr10 (at %) and near-equiatomic NiFeMnCoCr alloys by ~32% to ~1.1 GPa compared to those of boron-free reference materials with similar grain sizes. We will provide experimental proofs on the advent of such deformation-induced SROs on planar dislocation band structures, which can be successfully visualized by common dark-field TEM conditions.

J-84: Determination of Young’s Modulus and Phase Prediction using Classical Molecular Dynamics in Refractory HEAs: Ankit Roy1; Ganesh Balasubramanian1; 1Lehigh University
    High-entropy alloys (HEAs) are an exciting new class of alloys which have gained significant attention since 2004 due to the potential in showing promising mechanical properties. In this work we use classical molecular dynamics simulations to subject the alloys of the refractory Mo-Ta-Ti-W-Zr HEA family to tensile loading and obtain the Young’s modulus from the stress-strain behavior. The values of the Young’s modulus obtained are in reasonable agreement with the experimental values obtained by testing the synthesized samples. This validation ensures the correctness of the MD model. Following this, a structural pair correlation analysis (g (r)) in combination with common neighbor analysis (CNA) of the alloys are performed which together reveal the phases and crystal structures present in the alloys. The results of these predictions are compared with the XRD phase analysis and a good agreement is noted.

J-85: Developing Non-equiatomic Refractory BCC HEAs with Improved Mechanical Properties Using Combinatorial Screening: Taohid Bin Nur Tuhser1; Ian Winter2; Daryl Chrzan2; Andrew Minor2; Mark Asta2; Thomas Balk1; 1University of Kentucky; 2Lawrence Berkeley National Laboratory
     The optimum balance between ductility and hardness of refractory high entropy alloys (RHEAs) is strongly dependent on alloy composition, which need not be exactly equiatomic. In this study, 2D composition gradients of VNbMoTaW and VNbMoTaWHf thin films were made by magnetron sputtering. Replacing Mo with Nb in the same system is expected to improve ductility. X-ray diffraction and energy dispersive x-ray spectroscopy were used to develop a map of alloyphase space. The BCC crystal structure was stable for Nb ranging from 10.4 at% to 28.7 at% for VNbMoTaW and 8.4 at% to 22.6 at% for VNbMoTaWHf system. Bulk samples of varying Nb compositions were prepared using vacuum arc melting. Mechanical properties, including hardness and ductility of tensile specimens, were investigated with the bulk samples. Finally, a series of thermomechanical processing for selected compositions were done to check the phase stability and to establish appropriate composition-structure-property relationships.

J-86: Development of Metastable Nanolaminate High Entropy Alloy Overcoming Strength-ductility Trade-off: Minseok Kim1; Kook Noh Yoon1; Hyun Seok Oh2; Eun Soo Park1; 1Seoul National University; 2Massachusetts Institute of Technology
    Strength and ductility are the most important physical properties in evaluating structural materials. Unfortunately, common strengthening strategies in most conventional alloys cause sacrifice of ductility inevitably and vice versa. Recently, however, high-entropy alloy (HEA) is regarded as a good candidate that can overcome the strength-ductility trade-off. In the present study, we attempt to design the unique HEA microstructure with nano-thickness austenite film in hard martensite phase matrix. First of all, we made fully martensite HEA by controlling relative phase stability of martensite and austenite phase and severe deforming process. And then low temperature tempering process was performed for partial austenitization of the martensite. As a result, the HEA exhibited a novel ‘composite-like’ microstructure with metastability of the austenite film in martensite HEA matrix, which resulted in good ductility and strength balance. This result can provide a guideline on how to overcome strength-ductility trade off by tailoring microstructure in HEA.

J-87: Development of TiVNbTaW High Entropy Alloy with TRIPLEX Nanostructure: Sangjun Kim1; Jinyeon Kim1; Da Hye Song2; Jin Kyu Lee2; Eun Soo Park1; 1Seoul Nation University; 2Kongju National University
    Recently, various refractory high entropy alloys (RHEAs) have reported to exhibit superior mechanical properties especially at high temperatures comparing conventional Ni-based superalloy. However, RHEAs is their industrial application is limited due to the high melting temperature and poor ductility at room temperature etc. In the present study, we try to develop nanostructured RHEAs with novel mechanical properties. Preferentially, TiVNbTaW RHEA powder with single BCC phase was prepared by high-energy ball milling and sintered using spark plasma sintering. Interestingly, the sintered TiVNbTaW RHEA exhibited TRIPLEX nanostructure consisting of (Nb,Ta)-rich BCC, W-rich BCC and TiO FCC phase, which was formed during the sintering process by decomposition of single BCC phase in as-milled powder. Microstructural evolution of TRIPLEX nanostructure was analyzed in terms of metastable thermodynamic equilibrium and segregation of solute in a complex multi-principle system. This result could provide an effective guideline for tailoring the nanostructure of RHEAs fabricated by powder metallurgy.

J-88: Ductility of Quaternary Refractory Medium Entropy Alloys with Body-centered Cubic Structure: Qian He1; Shuhei Yoshida1; Tilak Bhattacharjee1; Nobuhiro Tsuji1; 1Kyoto University
    The present work focuses on the effect of homogenization on the ductility in HfNbTaTi, HfNbTaZr, HfNbTiZr, HfTaTiZr and NbTaTiZr refractory medium entropy alloys (MEAs). As-cast ingots of the MEAs were fabricated by vacuum arc-melting of pure metals and casting into a water-cooled copper mold under protective Ar atmosphere. Homogenization was then carried out to eliminate the elemental segregation in the as-cast samples. The results of tensile tests at room temperature indicated that although yield strength slightly decreased after homogenization, ductility greatly improved in HfNbTaTi, HfNbTaZr, HfNbTiZr, HfTaTiZr and NbTaTiZr MEAs. This suggested that segregation could heavily deteriorate the mechanical properties of MEAs, particularly the ductility. Besides, these results clearly showed that not only HfNbTaTiZr high entropy alloy (HEA) but also some equi-atomic quaternary MEAs exhibited ductile deformation behavior.

J-89: Effect of Sputtering Parameters on Structure and Mechanical Properties of TiZrHfNiCuCo High Entropy Alloy Films: Ki Buem Kim1; Young Seok Kim1; Taekjip Choi1; Jin Kyu Lee2; Hyo Soo Lee3; 1Sejong University; 2Kongju National University; 3Korea Institute of Industrial Technology (KITECH)
    The TiZrHfNiCuCo HEA metallic and nitride films on tungsten carbide substrate were successfully developed by a reactive direct current magnetron sputtering. At the low sputtering power, it can be seen that the compositional deviation of the films was clearly observed. With increasing the sputtering power, the films both metallic and nitride were composed of near equi-atomic ratios. Due to the high mixing entropy effect, large atomic radius difference, and rapid quenching effect, the structure of the metallic film revealed amorphous. With the addition of N2, structure of the nitride film was transformed to single FCC structure. The morphology of the metallic and nitride film was revealed as fine columnar structure with nano-scale pore. The atomic distribution of constituent elements of the nitride film was revealed to be nearly homogeneous. The hardness value of 16.6 GPa was obtained in the HEA nitride film.

J-90: Enhanced Mechanical Properties by Nitrogen Addition in N-CoCrNi and N-CoCrFeMnNi Compositionally Complex Alloy: Dennis Jodi1; Choi Nuri2; Joohyun Park2; Nokeun Park1; Timothy Alexander Listyawan1; 1Yeungnam University; 2Hanyang University
    In this study, we investigated the effect of nitrogen addition on phase formation and mechanical properties in the compositionally complex alloy (CCA) of N-CoCrNi and N-CoCrFeMnNi. Both the recrystallized N-CoCrNi and N-CoCrFeMnNi exhibited the formation of Cr2N precipitate on the microstructure. The Cr2N, combined with the presence of interstitial nitrogen in the matrix, was observed to hinder the grain growth of the face-centered cubic matrix, leading to the formation of fine grain sizes. The addition of nitrogen was also observed to improve the mechanical properties of N-CoCrNi and N-CoCrFeMnNi. This increase occurred as a result of various strengthening mechanisms of solid-solution, Hall-Petch strengthening, and precipitation strengthening by the addition of nitrogen.

J-91: Fabriacte and Mechanical Properties of Non-equiatomic High Entropally Reinforced 6082 al Matrix Nanocomposite: Anoushka Pal1; 1Indian Institute of Technology
    in the present investgation, al nanocomposites reinforced with non-equiatomic dual phase HEAwere synthesis by MM at 200 r.p.m for 50 h. in this investgation phase evolution, comp., morph. and stability of MM HEA powder were studied through XRD and TEM. Further effortswere made to hot press. microstructural characteristics and mechanical properties of tehse hea composite were studied through electron microscopy

J-92: Fabrication and Hardness Behavior of High Entropy Alloys: Modupeola Dada1; Patricia Popoola1; Ntombi Mathe2; Sisa Pityana2; Samson Adeosun3; Thabo Lengopeng2; 1Tshwane University of Technology; 2Council for Scientific and Industrial Research; 3University of Lagos, Akoka
    Laser additive manufacturing is a direct energy deposition process which manufactures components from 3D model data in progressive layers until a whole part is built as opposed subtractive manufacturing. However, during the procedure, the deposits are subjected to rapid thermal stresses which adversely impact the integrity of the built component. High entropy alloys are materials with complex compositions of multiple elements. Traditionally, these alloys are fabricated using casting and other machining processes, with a recent interest in the use of laser deposition as a possible manufacturing process. To optimize process parameters of high entropy alloys melted on a steel plate, the influence of preheating temperature on the overall quality, microstructure and hardness behaviour of the alloys for aerospace applications were investigated. In this research, 9 samples of AlCoCrFeNiCu and AlTiCrFeCoNi high entropy alloys were fabricated using different laser parameters. The phases, chemical composition, micro-hardness and structural morphologies were characterized with XRD, EDS, Vickers Microhardness tester and SEM respectively before and after preheating the base plates at 400C. Experimental results show extensive cracking on all the samples without preheating while after preheating all samples were observed to be crack-free. Although, there were no variations on the dendritic structures in the optical micrographs with and without preheating temperature, there were notable changes in the phases and hardness behaviour of the alloys showing that preheating the base plate from 400C significantly influences the mechanical properties of additive manufactured high entropy alloys and contributes to the elimination of cracks induced by thermal stresses.

J-93: Formation and Mechanical Properties of TaNbVTiW High Entropy Alloys Prepared by Powder Metallurgy: Da Hye Song1; Sangjun Kim2; Eun Soo Park2; Jin Kyu Lee1; 1Kongju National University; 2Seoul National University
     In general, refractory high entropy alloys(RHEAs) have been produced by vacuum arc melting due to the high melting temperature of component elements. As-casted RHEAs generally exhibit coarse dendritic structures and segregation which leading to undesirable the mechanical properties. High entropy alloys(HEAs) prepared by mechanical alloying and subsequent consolidation process are a promising method to obtain the homogeneous microstructures and enhanced mechanical properties.In this study, we report the formation and mechanical properties of the TaNbVTiW HEAs prepared by powder metallurgy. The HEAs synthesized by high energy ball milling followed by spark plasma sintering(SPS), vacuum hot pressing(VHP) and hot isostatic pressing(HIP). Structural characterization was performed using X-ray diffractometry (XRD) and scanning electron microscopy (SEM) with energy dispersive spectrometer (EDS). Compressive strength of HEAs was measured at room and elevated temperature with a strain rate of 1x10-4s-1.

J-94: Formation Zone Prediction of the Al-Co-Fe-Ni-Ti t High Entropy Alloys by High-throughput Calculation (HTC) Technique: Yu-Chun Li1; Chu-Hsuan Wang1; Hsien-Ming Hsiao2; Satoshi Ikubo3; Chuan Zhang4; Yee-Wen Yen5; 1Department of Materials Science and Engineering, National Taiwan University of Science and Technology; 2Institute of Nuclear Energy Research; 3Graduate School of Life Science and Systems Engineering, Kyushu Institute of Technology; 4CompuTherm LLC; 5National Taiwan University of Science and Technology
    In this study, the Pandat software was used with the PanHEA database. There were six points could form high-entropy alloys in the Al, Co, Fe, Ni, and Ti five-element system were calculated and selected for experiments. From the analysis of various results, it can be known that Alloy 2 (Al-31 at.% Co-33 at.% Fe-24 at.% Ni-6 at.% Ti) exhibits a single-phase solid solution structure, while the other five alloys is mainly composed of FCC phase and contains a relatively small amount of one or two other phases (L12, B2, H_21). The results obtained from the experiments are all in line with the calculated predictions. The experimental analysis of alloy hardness and corrosion was further carried out, and stainless steel 304 was used as a control group. The alloys in this study all have higher hardness than stainless steel 304, but are more corrosive and have a faster corrosion rate.

J-95: Generalized Planar Fault Energies and Twinning in NbMoTaW BCC High Entropy Alloy: A First-principles Study: Abu Anand1; Chandra Singh1; 1University of Toronto
    High entropy alloys of refractory elements have reported exhibiting superior mechanical properties while having low-density. In this work, we investigate the generalised fault energies of the BCC High Entropy Alloy system NbMoTaW using Density Functional Theory. Energy landscapes for twinning and slipping were calculated for NbMoTaW and compared with the component elements. The stacking fault and planar fault energy values for the HEA is lower than that of all component elements. Twinnability ratio (γ_TBM/∆us) was found to be 0.13 suggesting extensive deformation twinning in the HEA system. Origin of low fault energies was investigated using Integrated Crystal Orbit Hamilton Population (ICOHP). Except for W-Mo, W-Ta, interactions in NbMoTaW was found to be as weak as the Nb-Nb pure metal interactions which explain the reduced fault energies. Twin formation is less likely to happen near Tungsten rich portions of the alloy due to strong ICOHP interactions.

J-97: High Temperature Creep Behavior of AlZrCrMoNbTi High Entropy Alloy Using the Spark Plasma Sintering (SPS) System: Faris Sweidan1; Ho Jin Ryu1; 1KAIST, Korea
    During Spark Plasma Sintering, a correlation between the densification kinetics and compressive creep has been analyzed as creep was the main mechanism occurring in the densification final stage. After analyzing the parameters, it was found that they were in good agreement with those obtained from conventional creep experiments. In that sense, an SPS apparatus has been recently used as a creep testing system at higher temperatures than the limit of conventional creep testing apparatuses. Utilizing a special mold configuration, the creep behavior of AlZrCrMoNbTi high entropy alloy has been tested at several high temperatures and pressures that leads to the calculation of creep parameters, which are the activation energy and the stress exponent. As a result, The capability of SPS to be used as a creep test system provides access to obtaining the high temperature creep behavior of materials that will potentially be used in high temperature environments.

J-98: Homogenous Structure Formation in FeCoNiCrMo High Entropy Alloy: Ismael Hidalgo1; Lin Li2; Feng Yan2; Xiao Han2; 1University of Puerto Rico at Mayagez; 2University of Alabama
    In the past few decades, a new class of materials called High Entropy Alloys (HEAs) has been developed, revolutionizing the metallurgy field. In contrast to conventional alloys such as steel and superalloys, HEA’s are defined as multicomponent alloys with a concentrated blend of 5 or more elements forming a single alloy base. The unique structures of HEAs’ provide them with superior properties such as high strength, superconductivity, resistance to fatigue, fracture, corrosion and irradiation. In this work, a new FeCoNiCrMo HEA is fabricated using magnetron sputtering deposition. A comprehensive investigation on how the sputtering parameters control the deposited structures is performed. The structures are further validated by characterization techniques, such as X-ray diffraction and atomic force microscopy. This research work lays the foundation for future synthesis of advanced HEA’s with the purpose of creating a homogeneous phase.

J-99: Imaging Short Range Order in The CrCoNi Medium Entropy Alloy: Ruopeng Zhang1; Shiteng Zhao1; Jun Ding2; Yan Chong1; Qin Yu2; Colin Ophus2; Mark Asta2; Robert Ritchie2; Andrew Minor2; 1University of California, Berkeley; 2Lawrence Berkeley National Laboratory
    The equiatomic CoCrNi medium entropy alloy (MEA) exhibits exceptional high strength and ductility. The alloy is regarded as a random solid solution, yet the properties cannot be fully explained by solution hardening. Chemical short-range order could significantly affect the mechanical behaviors of alloys. While associated phenomena have been indirectly related to the deformation behaviors of MEA, direct observation of SRO by electron microscopy is challenging due to their intrinsically small scale and the diffuse nature of the structure. Here we report the verification of SRO in a thermal-mechanically treated MEA via high resolution (HRTEM) and energy-filtered TEM dark-field imaging (DF). By excluding the inelastically scattered electrons, superlattice-like diffraction pattern features from the SRO clusters could be detected. The size extent as well as the spatial distribution of the SRO clusters are directly resolved by DF imaging, which has been correlated to the effects on the mechanical behaviors of the MEA.

J-101: Influence of Compositional Complexity on Helium Accumulation and Bubble Formation in Concentrated Solid Solution Alloys: Shaofei Liu1; Da Chen1; Ji-jung Kai1; 1City University of Hong Kong
    High entropy alloys (HEAs) exhibit promising radiation damage tolerance due to their high-level lattice distortion and compositional complexity. The present work experimentally studied the helium accumulation and bubble formation in a group of HEAs with different principle components at different implantation temperatures. The size and population density of helium bubbles in the studied alloys were quantitatively analyzed through transmission electron microscopy, and the helium content existing in bubbles were estimated from a high-pressure Equation of State. It was found that the size and population density of helium bubbles differ with different compositional complexity. The helium diffusion in such condition was dominated by the different mechanism at different temperatures. Besides, the helium bubble formation mechanism and the activation energy of helium diffusion were analyzed based on Trinkaus’s model.

J-102: In-situ Neutron Diffraction Study on Stress-induced Phase Transformation in TiZrHfNbx Refractory High-entropy Alloys: Xuesong Fan1; Yan Chen2; Ke An2; Peter Liaw1; 1University of Tennessee; 2Oak Ridge 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 the TRIP (transformation-induced plasticity) steel, the stress-induced phase-transformation was also observed in the TiZrHfNbx refractory HEAs in previous studies. This concept can improve the ductility, which supplies the deficiency of BCC alloys and broaden the application of refractory HEAs. To deeply understand the deformation mechanisms of TiZrHfNbx alloys with different Nb-contents and at different temperatures, the in-situ neutron diffraction study was conducted in this work. Coupled with Scanning Electron Microscopy (SEM) with Backscatter Electron Detector (BSD), Energy Dispersive X-Ray Spectroscopy (EDS), Electron Backscatter Diffraction (EBSD), and Transmission Electron Microscopy (TEM) results, the concept will be further verified to benefit the design of HEAs with excellent properties.

J-103: Investigating BCC Refractory Multi-principal Element Alloys by Heaviside Digital Image Correlation: Leah Mills1; Jean-Charles Stinville1; Marie-Agathe Charpagne1; Valery Valle2; Noah Philips3; Oleg Senkov4; Tresa Pollock1; 1University of California, Santa Barbara; 2Institut PPrime; 3ATI Specialty Materials and Components; 4Air Force Research Laboratory
    Multi-Principal Element (MPE) alloys offer a new approach to design single-phase solid solutions through the addition of multiple elements in high concentrations, thus expanding upon the conventional alloy design space consisting of minor elemental additions to only one or two base elements. Motivated by their potential for extreme high-temperature applications, MPEs composed of refractory elements with high melting-points and body-centered cubic crystal structures exhibit promising mechanical properties compared to the more rigorously studied face-centered cubic MPEs. These refractory MPEs compel the study of underlying dislocation mechanisms in comparison to those observed in conventional BCC alloys. Innovative developments in SEM-DIC provided slip plane and direction analysis by elucidating slip trace geometry, heterogeneity of slip on a grain-to-grain basis and the tendency for plastic localization and transmission. This approach has been deployed for critical comparisons of the slip system behavior between pure Nb and two equiatomic MPEs: MoNbTi and HfNbTaTiZr.

J-104: Mechanical and Biocompatibility Evaluation of MoxNbTaxTiZr High and Medium Entropy Alloys for Biomedical Implants: Muhammad Akmal1; Ho Jin Ryu1; 1KAIST, Korea
    The MoNbTaTiZr high entropy alloys are promising for biomedical applications because of the excellent biocompatibility of constituting elements. In this work, MoNbTaTiZr medium and high entropy alloys with varying amount of Mo and Ta have been examined systematically. Whereas an increase in the yield strength is observed as a function of Mo and Ta content, however, their addition more than a critical value causes brittleness. This study accomplishes an optimum alloy system for biomedical applications, and then it was analyzed using cell culture and in-vivo biocompatibility evaluation in thigh muscles of mice. The alloy has shown strong osseointegration to osteoblasts and non-toxic response to muscular tissues.

J-105: Mechanical Properties and Deformation Behavior of NiTi-Based Low-, Medium- and High-Entropy Intermetallic Compounds at Different Temperatures: Cheng-Yuan Tsai1; Chi-Huan Tung1; Shou-Yi Chang1; 1National Tsing Hua University
    Shape memory alloys have the unique effects of shape memory and pseudoelastic response owing to martensitic transformations. In recent years, high-entropy intermetallic compounds have been developed to improve the shape memory and pseudoelastic performance. However, the martensitic transformation and dislocation activities in high-entropy compounds remain unclear because of their complex configuration and large lattice distortion. In this work, the mechanical response and deformation behavior of NiTi-based low-entropy (binary), medium-entropy (quaternary) and high-entropy (senary) intermetallic compounds were investigated by using nanoindentation and in-situ micropillar compression in SEM from cryogenic to high temperatures. Experimental results indicated that, in the low-entropy compound, a regular martensitic transformation yielded a typical deformation anisotropy and the interestingly ascending modulus/hardness with temperature. In comparison, in the high-entropy compound, the activities of abundant short-range defects prior to a martensitic transformation led to the uniform barrel-like deformation of the pillars and the descending mechanical properties with temperature.

J-106: Mechanical Properties and Discrete Slip Events in Conventional Alloys and High-entropy Alloys at Different Temperatures: Chun-Yi Chen1; Chi-Huan Tung1; Shou-Yi Chang1; 1National Tsing Hua University
    High-entropy alloys are being considered as prospective materials owing to their exceptional mechanical properties. Over the past few years, many investigations were conducted to find out the underlying mechanisms for their unique deformation behavior. In our previous study of in-situ micropillar compression, uniform gum-like deformation with abundant nucleation sites and short-range activities of defects was observed in several crystalline high-entropy systems, very different from the long-range dislocation gliding in conventional alloys. Herein, we further investigated the mechanical properties and deformation behavior of conventional face-centered cubic alloys and high-entropy alloys from cryogenic to high temperatures by using nanoindentation and in-situ micropillar compression in SEM. Experimental results indicated that the deformation anisotropy in the alloys might change with temperatures. The discrete slip events determined by the numerical analysis of ultraprecise displacement data revealed power-law scaling between the number of events and their magnitude, i.e. a scale-free behavior.

J-107: Mechanical Properties and Thermal Stability of Single-Target Deposited Ta-Ti-Zr-Based Quinary High-entropy Alloy and Nitride Coatings: Chin-Chun Chang1; Chia-Ying Yeh1; Hsiang-Ming Lai1; Yu-Ting Hsiao1; Shou-Yi Chang1; 1National Tsing Hua University
    Multi-component alloy and nitride coatings have been developed to improve the mechanical performance, thermal stability and wear/oxidation resistance of protective hard coatings. High-entropy coatings with a simple solid-solution structure have particularly attracted great interest in recent years. In this study, several coatings of Ta-Ti-Zr-based quinary high-entropy alloys and nitrides with the additions of Al, Cr, Hf, Mo and/or Nb were deposited using a single-target sputtering system in an N2/Ar mixed atmosphere. Most of the high-entropy alloy coatings exhibited a near-amorphous structure, while the nitride coatings had a simple face-centered cubic solid-solution structure. Compared to traditional hard coatings, the high-entropy alloy coatings easily had a hardness up to 10 GPa, and the nitride coatings had a hardness of 30 GP and a better thermal stability/oxidation resistance. The elements Hf, Mo and Nb were found to improve the mechanical properties, and Cr, Ta and Zr to improve the oxidation resistance.

J-108: Microalloying Technology: an Attractive Strategy for the Design of High-entropy Alloys: Wenyi Huo1; Feng Fang1; Jianku Shang2; Jianqing Jiang1; 1Southeast University; 2University of Illinois at Urbana-Champaign
    Microalloyed CoCrFeNi high-entropy alloys were produced by magnetron sputtering. In this work, Pd, Ag and Ce were selected as the microalloyed element for CoCrFeNi alloys, respectively. The content of the microalloying element in the high-entropy alloys is less than 1.0 at.%. Via nano-indentation technology, it shows that compared with the high hardness of the unalloyed samples (i.e., 8.5 GPa), the hardness of the microalloyed samples was further greatly improved (e.g., as high as 10~11 GPa). By XRD, face-centered cubic structure was identified in microalloyed CoCrFeNi high-entropy alloys. Nanotwins and nanocrystalline are further characterized by TEM. In addition, the increase in resistivity also confirms the strengthening effects of microalloying in high entropy alloys. The work shows that each high-entropy alloy could be as an alloy base, and may be modified to achieve superior properties by microalloying.

J-109: Microstructure and Magnetic Behavior of FeCoNi(Mn–Si)x (x=0.5,0.75,1.0) High-entropy Alloys: Priyanka Sahu1; Suresh Solanki2; Sheetal Dewangan1; Vinod Kumar1; 1Indian Institute of Technology Indore; 2Global Institute of Technology, Jaipur, India
    FeCoNi(Mn–Si)x (x 5 0.5, 0.75, 1.0) high-entropy alloys (HEAs) were synthesized by mechanical alloying (MA) and the effect of Mn and Si in the ferromagnetic alloys on crystal structure and magnetic behavior was investigated. XRD, SEM, and TEM were used to investigate the effect of Mn and Si content on the structure of HEAs. The rise in Mn and Si content change the structure from the BCC to FCC phase. The surface morphology was discussed based on MA time and content of Mn and Si. The magnetic hysteresis loop shows the highest magnetic saturation (Ms) of 134.21 emu/g for FeCoNi (Mn–Si)1.0 alloy and low coercivity (Hc) of 98.07 Oe for FeCoNi(Mn–Si)0.5 alloy. The finite element method (FEM) using COMSOL Multiphysics software has been used for determining the magnetic flux density (B) on the surface and at the center of the transformer core to determine the performance of HEAs.

J-110: Microstructure and Mechanical Properties of an Equiatomic CoCrFeMnNi High Entropy Alloys Fabricated by Gas Atomization: Cheenepalli Nagarjuna1; Kwang Yong Jeong1; Hyeon Jeong You1; Gian Song1; Jin Kyu Lee1; Soon Jik Hong1; 1Kongju National University
    In this study, an equiatomic CoCrFeMnNi high entropy alloys (HEAs) fabricated by using a combination of gas atomization, mechanical milling and spark plasma sintering processes. The phase identification and morphological studied of alloy powders have been investigated by the X-ray diffraction and SEM analysis respectively. The grain refinement mechanism and chemical composition behavior was examined with mechanical milling time. Moreover, we investigated the mechanical properties such as Vickers hardness and compressive strength of HEAs under different milling times. In order to understand the failure mechanism during compression test, we studied the cross-sectional microstructure of the compressive samples for analyzing the kind of fracture occurred with grain sizes. The results revealed that a significant improvement of hardness and compressive strengths for the fine-grained microstructure than coarse grained microstructure. It is mainly attributed to the gain boundary strengthening behavior and the obtained results followed the Hall-Petch relationship.

J-111: Microstructure and Mechanical Properties of Non-equiatomic Fe-Mn-Ni-Cr-Co-Al-Ti Septenary High Entropy Alloy: S. Varalakshmi1; Yagnesh Shadangi1; R. Manna1; N. K. Mukhopadhyay1; 1Indian Institute of Technology (BHU) Varanasi
    In the present investigation, efforts were made to fabricate non-equiatomic Fe-Mn-Ni-Cr-Co-Al-Ti septenary Fe based high-entropy alloy (HEA). The Fe based HEA was fabricated using vacuum induction melting in a magnesia crucible and as-cast into a plate of 2.5 kg. The phase evolution, chemical composition and thermal stability of these alloy were established through X-Ray diffraction (XRD), Transmission electron microscopy (TEM), Scanning electron microscopy and Differential scanning calorimetry (DSC) respectively. The objective of this work is to study the precipitation of the L12 type phase (Ni3(Al, Ti)) in the Fe based HEA matrix. Furthermore, efforts were made to study the mechanical properties of these by using instrumented indentation technique and tensile testing. The current work is a good attempt towards the exploration of Fe-based HEAs to find their scope in structural applications.

J-112: Microstructure and Tribological Behavior of Non-equiatomic Ti-Zr-Cr-Al-Si-V and Ti-Zr-Cr-Al-Si-V-Nb Refractory High Entropy Alloys: Harsh Jain1; Yagnesh Shadangi1; Vikas Shivam1; Nilay Mukhopadhyay1; Devendra Kumar1; 1IIT BHU
    The aim of the present work is to synthesize the non-equiatomic composition of refractory high entropy alloy by vacuum arc melting. It is shown that the calculated lattice parameters, phase stability, hardness and wear property of non- equiatomic RHEAs TiZrCrAlSiV and TiZrCrAlSiVNb are consistent with the available experimental and theoretical. The systematic alloying behavior of the alloys was followed by X-ray diffraction, scanning electron microscopy (SEM), transmission electron microscopy (TEM). Despite containing many constituents, both alloys had a single-phase body-centered cubic (BCC) structure. Vickers hardness and wear rate at room temperature (RT) of the alloy calculated by Vickers hardness tester and pin on disk respectively. The theoretical density of the alloys was varying in the range of 5-5.2 gm/cc. The exceptional microhardness in these alloys is greater than any individual constituent, suggesting the operation of a solid-solution-like strengthening mechanism.

J-113: Microstructure Characterization of Oxide Dispersion Strengthened CoCrFeMnNi High Entropy Alloy Synthesized by Cryo-milling and Spark Plasma Sintering: Seunghyeok Chung1; Bin Lee2; Soo Yeol Lee3; Ho Jin Ryu1; 1KAIST; 2KITECH; 3CNU
    The effects of alloyed powder preparation, cryo-milling conditions and spark plasma sintering conditions on the nanostructures of oxide dispersion strengthened (ODS) CoCrFeMnNi high entropy alloys (HEAs) were investigated to enhance the high temperature strength and irradiation resistance further. In order to control the oxide dispersoids size and distribution, the mixture of CoCrFeMnNi atomized powder and 0.5wt%Y2O3 powder, and CoCrFeMnNi-0.5wt%Y atomized powder were prepared and cryo-milled at 97 K, respectively. After spark plasma sintering at 973, 1073, 1173 K, the microstructures of oxide dispersoids and the HEA matrix are characterized by EBSD, SEM, TEM, EDS and SANS. The size of oxide dispersoids and the grain size of CoCrFeMnNi decreased with spark plasma sintering temperature. We found that the use of CoCrFeMnNi-0.5wt%Y enhanced the refinement of oxide dispersoids in the CoCrFeMnNi HEA matrix. The mechanical properties measured by Vickers hardness and nanoindentation were significantly enhanced in ODS-HEA prepared with CoCrFeMnNi-0.5Ywt% atomized powder.

J-114: Microstructure Evolution and Enhanced Strength in CoCrFeMnNi Alloy through High Speed Shear Loading: Toru Murata1; Nobuhiro Imakura1; Alok Singh2; Ivan Gutierrez-Urrutia2; Koichi Tsuchiya2; Naoko Ikeo1; Toshiji Mukai1; 1Department of Mechanical Engineering, Graduate School of Engineering, Kobe University; 2National Institute for Materials Science (NIMS)
    High entropy alloys (HEAs) have been expected to be used for structural applications due to their excellent mechanical properties. Since grain refinement is effective for strengthening the HEAs, ultra-fine-grained materials have been fabricated through various plastic deformation processes. The microstructure evolution is often dominated by cumulative shear deformation. In this study, effect of localized plastic strain was investigated on the microstructure evolution in a hat shape specimen of an equiatomic CoCrFeMnNi alloy. Localized shear deformation was applied to a fixed shear displacement in a wide range of strain rates. On the other hand, finite element analysis (FEA) was conducted under the same conditions as the experiments to predict strain distribution in the specimens. As a result, it was found that deformation twins and ultra-fine grains were formed according to the certain cumulative strain.

J-115: New Approaches for Exploration of Refractory Multi-principal Element Alloys: Carolina Frey1; Chris Borg2; James Saal2; Bryce Meredig2; Daniel Miracle3; Tresa Pollock1; 1University of California, Santa Barbara; 2Citrine Informatics; 3Air Force Research Laboratory
    Refractory multi-principal element alloys (RMPEs) comprised of Hf, Mo, Nb, Ru, Ta, W and / or Zr are of interest for high temperature applications. Relative to their FCC counterparts, the composition space for RMPEs remains relatively underexplored, due to difficult processing paths and high melting points. This presentation will discuss sequential alloy design of RMPEs guided by machine learning approaches that are coupled with rapid processing and characterization. Building on a recently published refractory alloy database, a machine learning model was trained to identify promising compositions. Experimental methods, including splat quenching as a rapid solidification technique and thin foil tensile testing have been developed to rapidly explore novel RMPE compositions with interesting properties. New compositions with high strength will be discussed.

J-116: On the Phase Transformation and Dynamic Stress-strain Partitioning of Ferrous Medium-entropy Alloy Using Integrated Analysis: Jae Wung Bae1; Jaimyun Jung1; Jung Gi Kim2; Jeong Min Park1; Stefanus Harjo3; Takuro Kawasaki3; Hyoung Seop Kim1; 1POSTECH; 2Gyeongsang National University; 3Japan Proton Accelerator Research Complex
    In the present study, an integrated experimental-numerical analysis on ferrous medium-entropy alloy (FMEA) was conducted to understand the micromechanical response of the constituent phases in the FMEA at −137 C. The initial face-centered cubic (FCC) single phase microstructure of the FMEA was transformed to body-centered cubic (BCC) martensite during tensile deformation at −137 C, resulting in improved low-temperature mechanical properties. The microstructure evolution due to deformation-induced phase transformation mechanism and strain partitioning behavior was analyzed using ex-situ electron backscatter diffraction. The mechanical responses related to the stress partitioning between constituent phases and deformation-induced transformation rate were measured using in-situ neutron diffraction in combination with the nanoindentation analysis. Three-dimensional microstructure volume element based crystal plasticity models were built based on the experimental observations. The concurrent analysis by means of the integrated methodology revealed the origin of superior strain hardening capability and the resulting outstanding low-temperature mechanical properties.

J-117: Overcoming Strength-ductility Trade-off in Additively Manufactured 1%C-CoCrFeMnNi High-entropy Alloy Induced by Hierarchically Heterogeneous Microstructure: Jeong Min Park1; Jung Gi Kim2; Jungho Choe3; Jae Wung Bae1; Jongun Moon1; Ji-Hun Yu3; Hyoung Seop Kim1; 1POSTECH; 2Gyeongsang National University; 3Korea Institute of Materials Science
    In this study, 1%C-CoCrFeMnNi high-entropy alloys (C-HEAs) were additively manufactured using selective laser melting (SLM). The alloys exhibited significant improvement of tensile properties after the SLM process as compared with not only as-cast conditions but also other SLM-processed HEAs previously reported. The superior tensile properties of the as-built C-HEAs could be attributed to their hierarchically heterogeneous microstructure with combination of various strengthening mechanisms. In particular, the SLM process could allow to maximize the strengthening effect of carbon addition to HEAs via finely distributed nano-carbides at the boundaries of solidification cellular structure. In addition, the samples built at different scanning speeds exhibited different levels of strength, as explored by comparing each strengthening contribution. This work will open a new window to utilize SLM process for enhanced mechanical properties of HEAs with great potential.

J-118: Oxidation Behavior of Al4Co3Cr25Cu10Fe25Ni33 at High Temperature: Ching-Nien Tsai1; Feng-Yi Cho1; Fan-Yi Ouyang1; 1National Tsing Hua University
    High entropy alloys (HEA) has recently attracted considerable interest and attention due to their novel properties of better corrosion resistance and superior mechanical strength at high temperature. In this study, we investigate the oxidation behavior of Al4Co3Cr25Cu10Fe25Ni33 HEA at temperature raging from 800 C to 950 C. Firstly, the HEA with composition of Al4Co3Cr25Cu10Fe25Ni33 was fabricated by Vacuum Arc Melting (VAM) method, and then the oxidation tests were performed using thermo-gravimetric analyzer at 800 C, 850 C, 900 C, and 950 C under the atmosphere of Ar and O2 up for 24 h, respectively. The results show that the weight gain of the samples increases with increasing temperature. In addition, we observed specimens exhibit preferential intergranular oxidation and bilayer scales, Cr2O3/Al2O3, were found after oxidation process. The microstructure evolution and mechanism of the oxidation behavior of the HEA will be discussed in details.

J-119: Partitioning Behavior Based Design of BCC / B2 Dual-phase Refractory Multi-principal Element Alloys: Hosun Jun1; Pyuck-Pa Choi1; Zhiming Li2; Dierk Raabe2; 1Korea Advanced Institute of Science and Engineering (KAIST); 2Max-Planck-Institut fr Eisenforschung GmbH
     Refractory multi-principal element alloys (MPEAs) have received attention for their outstanding high temperature strength. Refractory MPEAs with a BCC matrix and coherent B2 precipitates are expected to have further improved creep resistance at elevated temperature by precipitation hardening effect. In this research, refractory MPEAs with BCC matrix / B2 precipitate microstructure were designed by a novel approach of mixing two virtual base alloys, namely Ti-25 at.% Nb and HfAl. Their mixing ratio was controlled to form a supersaturated solution after homogenization and induce phase separation during an ageing treatment. Ageing temperature and time were varied for systematical studies of elemental partitioning behavior. The microstructure of alloys after heat treatment were studied by multiple characterization techniques including X-ray diffraction, transmission electron microscopy (TEM), and atom probe tomography (APT). Results showed that refractory MPEAs with a BCC matrix and coherent B2 nanoprecipitates of 0.5~0.8nm in size could be successfully fabricated.

J-120: Phase Field Dislocation Dynamics Modeling of Refractory High Entropy Alloys: Lauren Fey1; Shuozhi Xu1; Yanqing Su1; Abigail Hunter2; Irene Beyerlein1; 1University of California, Santa Barbara; 2Los Alamos National Laboratory
    Refractory multi-principle element alloys show great potential for high-temperature applications, but their deformation mechanisms are not well understood. Since deformation of these materials in mediated by slip, there is a strong motivation to understand dislocation behavior in these alloys. To study this, we develop a phase field dislocation dynamics (PFDD) model. Because screw dislocations are known to dominate behavior in BCC metals, a dislocation character dependence is added to the PFDD model by adjusting the lattice energy, which accounts for the dislocation cores. Additionally, the random chemical variations of the disordered solid solution phase are modelled via a position-dependent lattice energy. This model can be applied to a ternary MoNbTi alloy by incorporating the distribution of DFT-calculated unstable stacking fault energies. The results of this model on the behavior of Frank-Read sources will be presented.

J-121: Phase Stability and Defect Properties of fcc FeCrMnNi HEAs: Mark Fedorov1; Jan Wrbel1; Antonio Fernndez-Caballero2; Krzysztof Kurzydłowski3; Duc Nguyen-Manh4; 1Faculty of Materials Engineering, Warsaw University of Technology; 2EPSRC Centre for Doctoral Training in Materials for Demanding Environments, Faculty of Science and Engineering, University of Manchester; 3Faculty of Mechanical Engineering, Bialystok University of Technology; 4Culham Centre for Fusion Energy, United Kingdom Atomic Energy Authority
    Multi-component alloy Fe-Cr-Mn-Ni is a promising candidate system for application as structural material beyond conventional austenitic steels, especially in irradiation conditions. We have developed the Cluster Expansion model for the Fe-Cr-Mn-Ni system based on DFT calculations and performed subsequent Monte Carlo simulations to study the concentration dependence of phase stability at 0K and finite temperatures. Order-disorder transition temperatures for the majority of compositions correlate with the percent of L10-MnNi phase, which is the most stable at 0K in this system. Stabilizing effect of configurational entropy is prominent in the intermediate temperature region, where order-disorder transition occurs. Difference in magneto-volume relation in FeCrNi and FeCrMnNi hints on the difference in the behavior under irradiation. Interstitial and vacancy migration properties have been studied using NEB calculations in equiatomic and Fe27Cr18Mn27Ni28 compositions and analyzed as the function of the diffusing element, nearest neighbourhood and the level of short range order in the system.

J-122: Phase Stability and Microstructural Evolution in Refractory High Entropy Superalloy: Sangjun Kim1; Hyunseok Oh1; Kook Noh Yoon1; Eun Soo Park1; 1Seoul Nation University
    Recently, various refractory high entropy superalloys reported, which have unique microstructure containing cuboidal nano-precipitates in BCC high entropy alloy (HEA). They exhibited superior mechanical properties at both ambient and high temperature. However, there are many unsolved issues to attract even greater attention such as precipitation control of unwanted compounds, optimal phase selection between ordered and disordered BCC, and optimization of mechanical properties etc. In the present study, we propose how to tailor the microstructure of refractory high entropy superalloy in Ti-Zr-Hf-Nb-Ta-Al HEAs. Microstructural evolution for the non-equiatomic HEA compositions and the effects of minor alloying elements were systematically investigated by considering phase transformation mechanism as well as phase equilibria. This result could provide an effective guideline for tailoring microstructure of refractory HEAs with ordered and disordered BCC phases, and developing a promising high entropy superalloy with customized microstructure for ultra-high temperature structural application.

J-123: Phase Stability of a Group of fcc-structured Medium-entropy Alloys under High Pressure and High Temperature: Fei Zhang1; Hongbo Lou1; Yuan Wu2; Zhaoping Lu2; Qiaoshi Zeng1; 1Center for High Pressure Science & Technology Advanced Research; 2University of Science and Technology Beijing (USTB)
    The prototype equiatomic high-entropy alloy (HEA) CoCrFeMnNi usually crystallizes into a single solid solution phase with a face-centered cubic (FCC) crystal structure. Under high pressure, the CoCrFeMnNi was reported to have an FCC to HCP polymorphic phase transition. Meanwhile, a similar phase transition was also observed in the CoCrFeNi alloy. Whether the polymorphism is general in HEAs and how does the composition affect the transition remain unclear. To address these questions, we employ in situ high-pressure and high-temperature synchrotron radiation X-ray diffraction, X-ray emission spectroscopy and ex-situ transmission electron microscopy techniques, and systematically investigate the structure evolution of the subgroup medium-entropy alloys of the CoCrFeMnNi HEA under high pressure (e.g., FeCoNiCr, FeCoNiMn, NiCoCrMn, FeCoNi, FeNiMn, FeNiCr, NiCoCr, NiCoMn). The mechanism for the polymorphic FCC to HCP transition is discussed based on the highly composition-dependent phenomena.

J-124: Physical Origin of Mechanical Behavior of NbTaTiV(Zr) High Entropy Alloy from First-principles Simulations: Qi An1; Jing Zhang1; Hongwei Wang1; Chan-Ho Lee2; Peter Liaw2; 1University of Nevada, Reno; 2The University of Tennessee
    Designing novel high entropy alloys (HEAs) with high strength and great ductility is essential for their massive manufacture process and extended engineering applications. However, the underlying atomistic mechanisms leading to these improved mechanical properties are less explored, compared to traditional metal and alloys. Recent experiments observed that the strength of the NbTaTiV HEA could be significantly enhanced by adding another component Zr to form the NbTaTiVZr HEA. It was suggested that the improved strength originates from the increased lattice distortion due to the incorporation of Zr. To illustrate the physical origin of this enhanced strength, we performed the DFT simulations on both NbTaTiVZr and NbTaTiV systems to investigate their general stacking fault (GSF) energy surface.The effects of Zr component on the GSF surface and energy barriers are predicted, and this effect is explained by the metallic-bonding analysis.This study explains the enhanced strength from the atomistic point of view.

J-125: Preparation of CoCrFeNi High-entropy Alloy via Electro-deoxidation of Metal Oxides: Yu Yang1; Tongxiang Ma1; Mengjun Hu1; Pengjie Liu1; Liangying Wen1; Liwen Hu1; Meilong1; 1Chongqing University
    High entropy alloys (HEAs) have attracted extensive attention due to their excellent properties for various applications. In this work, single-phase equiatomic CoCrFeNi high-entropy alloy (HEA) was prepared by one-step electrolysis of solid oxides in molten CaCl2 at 900℃. The effect of solid oxides porosity on the current efficiency and mechanical property were investigated using electrochemical workstation and Vickers hardness tester. The Vickers hardness and current efficiency of as-prepared CoCrFeNi alloy are negatively correlated with solid oxides porosity. Varying the porosity of solid oxides, the CoCrFeNi HEAs ranging from powders to solid block could be prepared which provides a possibility for additive manufacturing. The corrosion behavior of the CoCrFeNi HEA is excellent in different aqueous solution which investigated by polarization curve tests. The aim of the current study is to highlight the versatility of a simple electrochemical method for HEAs preparation in a straightforward, low-energy and cost-affordable process.

J-126: Significance of Grain Refinement in HfNbTiZr and CoCrFeNi High-entropy Alloys: Wenrui Zhao1; Jae-Kyung Han1; Megumi Kawasaki1; 1Oregon state Univesity
    Recent studies show that high entropy alloys (HEAs)perform excellent microstructural stability and mechanical properties under a wide range of temperature. With applying a well-recognized grain refining technique of high-pressure torsion (HPT), HEAs enable to demonstrate further improvements in mechanical properties. The present study applies HPT on two different HEAs of HfNbTiZr and CoCrFeNi for up to 10 turns under 6.0 GPa, and evaluates the differences between the HEAs in the following three aspects. First, the difference in Vickers microhardness evolution is evaluated with increasing numbers of HPT turns. Second, strength and ductility are examined after HPT by applying micro tensile testing. Third, the texture evolution through HPT is examined by X-ray diffraction analysis. This presentation places a special emphasis on the significance of grain refinement by HPT on the two HEAs in terms of both physical and mechanical properties.

J-127: Solute and Self-diffusion in HCP High Entropy Alloys: Sandipan Sen1; Mayur Vaidya1; Xi Zhang2; Lukasz Rogal3; Blazej Grabowski4; Gerhard Wilde1; Sergiy Divinski1; 1University of Mnster; 2Max-Planck-Institut fr Eisenforschung GmbH; 3Institute of Metallurgy and Materials Science of the Polish Academy of Sciences; 4University of Stuttgart
     For the first time, diffusion in HCP HEAs is investigated using tracer technique. Solute diffusion (Co) and self-diffusion (Ti) are studied in HfZr, HfZrTi, Al5Hf25Sc20Ti25Zr25 and Al15Hf25Sc10Ti25Zr25 alloys in the temperature range of 400C-1100 ⁰C. The impact of increasing number of elements and of Al-content in quinary alloys on the diffusion behavior is examined. The alloys were prepared from 99.99% purity elements in an arc-melting furnace with a water-cooled copper plate under a protective Ar atmosphere. X-ray diffraction confirms the presence of a single-phase HCP structure. Ultra-fast diffusion of Co is highlighted for these alloys, similar to observations for α-Zr. Both solute(Co) and self(Zr) diffusion rates decrease with increasing of number of elements, when compared on the homologous temperature scale. The experimental findings are explained by utilizing density-functional-theory-based calculations.

J-128: Stress Corrosion Cracking Mechanism of FCC Type High-entropy Alloys Structural Materials under High Temperature Pressurized Water Environment by Molecular Dynamics Simulation: Chang Liu1; Qian Chen1; Yang Wang1; Narumasa Miyazaki1; Yusuke Ootani1; Nobuki Ozawa1; Momoji Kubo1; 1Tohoku University
    For the practical use of FCC type high-entropy alloy (HEA) with excellent high-temperature strength, it is required to obtain principles on how to prevent stress corrosion cracking. Consequently, it is important to elucidate the mechanism in corrosion and the intergranular fracture process of HEA caused by stress in high temperature pressurized water environment. For this purpose, here the tensile simulation was performed on the grain boundary model of FCC type HEA in vacuum and water environment by reactive molecular dynamics method. In vacuum environment, the stacking faults via a structural transformation from FCC to HCP were generated from the grain boundaries and surfaces. However, in water environment, the stacking faults were suppressed because the HEA surface was oxidized by water, and a change from the FCC to the BCC structure was observed instead. This behavior differs from the pure metal like nickel, showing the unique stress corrosion cracking mechanism.

J-129: Structural Evolution and Thermal Stability of Nanocrystalline High Entropy Alloy through Cryomilling: Harshavardhan Saragadam1; Yagnesh Shadangi1; Bhaskar Majumdar2; Nilay Krishna Mukhopadhyay1; 1IIT(BHU)-VARANASI; 2Defence Metallurgical Research Laboratory, Hyderabad
     The high-entropy alloys (HEA) exhibits unique properties in term of microstructural stability and mechanical strength. It is of paramount importance to fabricate nanocrystalline HEAs in bulk quantity for prospective coating application and need also to establish its thermal stability. In the present investigation a non-equiatomic Al-Si-Cr-Mn-Fe-Ni-Cu HEA was prepared by vacuum induction melting followed by cryomilling (CM) at 123 K upto 10h. The phase evolution/ composition, morphology and thermal stability of CM HEAs powder were studied through XRD, TEM, SEM and DSC respectively. Further efforts were made to consolidate the CM HEAs by spark plasma sintering (SPS). The microstructural characteristics and mechanical properties of these HEAs were studied through electron microscopy and instrumented indentation techniques. The present study provides an insight into the microstructural evolutions and the thermal stability of nanocrystalline HEAs subjected to CM. KEYWORDS: High-entropy alloy; Cryomilling; Spark Plasma Sintering; Instrumented indentation.

J-130: Synthesis and Phase Stability of High-entropy Nitrides and Carbonitrides: Olivia Dippo1; Tyler Harrington1; Neda Mesgarzadeh1; Kenneth Vecchio1; 1University of California, San Diego
    Ultra-high temperature ceramics (UHTCs) are critical materials for aerospace applications, such as on leading edges of supersonic aircraft. UHTCs such as transition metal carbides and nitrides have inherently favorable properties, as they are amongst some of the highest melting temperature materials. High-entropy versions of these UHTC compounds have the potential to elevate their high-temperature phase stability due to entropic stabilization. High-entropy transition metal nitrides and carbonitrides were experimentally fabricated in bulk sample form. Powder processing, bulk material densification, and single-phase character of resulting high-entropy ceramic materials were studied. Phase determination of various compositions was done using X-ray diffraction, and chemical homogeneity was characterized using energy dispersive X-ray spectroscopy. This work demonstrates the ability to continue to expand the field of high entropy alloys to include single-phase high entropy, ultra-high temperature nitrides and carbonitrides.

J-131: Temperature Dependence of Structural and Magnetic Properties of Single-crystal CoCrFeNiMn-based Alloys: Guo-Yu Hung1; Yao-Jen Chang2; Chi-Hung Lee3; Yi-Jia Chen4; Uwe Glatzel5; An-Chou Yeh2; Wen-Hsien Li3; Ssu-Yen Huang4; Nadya Mesti1; Bo-Hong Lai1; Tu-Ngoc Lam1; E-Wen Huang1; 1National Chiao Tung University; 2National Tsing Hua University; 3National Central University; 4National Taiwan University; 5University Bayreuth, Bayreuth
    To study the Manganese (Mn) effects on magnetic properties of high entropy alloys (HEAs), we prepared a single-crystal (CoCrFeNi)xMn1-x to eliminate the grain boundary effects. The samples with concentration gradients of Mn are sliced at different portions with different Mn contents. The magnetic and structural properties of (CoCrFeNi)xMn1-x are examined as a function of temperature. We found that Mn content and magnetic properties have positive correlations. Our neutron diffraction data also show the Mn effect on the diffraction profiles.

J-132: The Development of High Performance Hybrid High Entropy Alloys(HEAs): Weicheng Heng1; Daixiu Wei1; Hidemi Kato1; Akihiko Chiba1; 1Institute of Materials Research, Tohoku University
    The high phase stability and excellent mechanical properties of high entropy alloys (HEAs) give them great potential for use, particularly as structural materials. However, because the advantages of these alloys are limited to a small temperature range, they are not suitable for use without significant modifications. The focus of this study was the design of a new series of hybrid high entropy alloys capable of maintaining their characteristics over a wide temperature range by combining two types of conventional HEAs. A series of three hybrid high entropy alloys, (CoCrFeNi)100-x(TaNbMoW)x (x=2, 4, 6) was fabricated. Their microstructure was examined by SEM and EBSD, and the composition of the precipitates and the interface between matrix and precipitates was examined by TEM. These hybrid HEAs were found to have higher strength at room temperature and less strength loss at elevated temperatures than conventional HEAs under the same condition.

J-133: Theoretical and Experimental Investigation of Phase Structure and Mechanical Property Dependence on Composition in Nb-Ti-V-Zr Multi-principal Element Alloys: Mu Li1; Zhaohan Zhang1; Arashdeep Thind1; Rohan Mishra1; Katharine Flores1; 1Washington University in St. Louis
    Factors that affect the stability of single phase solid solutions in multi-principal element alloys (MPEAs) are unclear despite several empirical predictive models. In this work, the variation in phase structure with composition in NbTixVZr was investigated using a high-throughput, laser deposition-based synthesis method. The stability of the observed phases was further investigated using density functional theory (DFT) calculations. We find that the stability of a single phase solid solution does not correlate with compositional complexity. Multiple phases were observed in equimolar NbVZr, including BCC solid solution, C14 (hexagonal) and C15 (cubic) Laves phases; the C14 was previously reported to be unstable. The addition of Ti results in the stabilization of single BCC solid solution. We also observe stacking faults in the Laves phases and calculate their stacking fault energies with DFT. Ongoing nanoindentation and micropillar compression measurements will provide an improved understanding of the structure-property correlation in this MPEA system.

J-134: Tuning Microstructure of Refractory High-entropy Alloys via Controlling Cooling Rates: Hailong Huang1; Zhaoping Lu1; 1University of Science and Technology Beijing
    Three equatomic TaHfZrTi, NbHfZrTi and TaNbHfZrTi refractory high entropy alloys (HEAs) were synthesized by arc-melting and subjected to solution treatment, followed by three cooling conditions, namely, furnace cooling (FC), air cooling (AC) and water quenching (WQ). The microstructure, phase constitution and mechanical properties of these heat treated RHEAs were characterized. Surprisingly, strong dependence of microstructures on cooling rates was revealed in the TaHfZrTi and TaNbHfZrTi, but not in the NbHfZrTi. The TaHfZrTi remains a BCC (body centered cubic) lattice in WQ samples and decomposes into two BCC phases with different lattice parameters in AC samples with a slower cooling rate. The phase decomposition in the FC TaHfZrTi is more complete; BCC Ta-rich and hexagonal-close-packed (HCP) Ti-rich precipitates form in the matrix BCC. Our results indicate that processing conditions in some HEAs like TaHfZrTi needs to be carefully controlled as far as the structural stability is considered.

J-135: Wire +Arc Additive Manufacturing of AlCoCrFeNi High Entropy Alloy: Rumman Ahsan1; Gi-Jeong Seo1; Xuesong Fan2; Yousub Lee3; P. K. Liaw2; Duck Bong Kim1; 1Tennessee Technological University; 2The University of Tennessee, Knoxville; 3Oak Ridge National Laboratory
    Gas tungsten arc (GTA) based Wire+arc additive manufacturing (WAAM) can deposit any metallic material due to its inherent independent control of the arc. Additive manufacturing of high entropy alloys (HEAs) combines the extraordinary mechanical properties of the new family of alloys with flexibility with geometry and complexity of the process. In this work, a GTA-WAAM approach is presented for near net shaped deposition from a pre-alloyed and extruded AlCoCrFeNi HEA. The microstructure of the as-deposited HEA was investigated and compared with the arc melted HEA of the same composition. A strong influence of the high heat input followed by a rapid solidification along with a directional nature of cooling was observed on the amount of phases, their composition and spatial distribution were observed. It is concluded that GTA-WAAM can be a versatile tool for additive manufacturing with HEAs, despite the challenges involved to have a controlled microstructure.