Advances in Multi-Principal Elements Alloys X: Alloy Development and Properties: On-Demand Oral Presentations
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; Jennifer Carter, Case Western Reserve University; Srivatsan Tirumalai; Xie Xie, FCA US LLC; Gongyao Wang, Globus Medical

Monday 8:00 AM
March 14, 2022
Room: Advanced Materials
Location: On-Demand Room

Strengthening in HEAs by Solute-solute Interactions and Short-range-order: William Curtin1; Shankha Nag2; Binglun Yin3; 1Epfl Sti Igm Lammm; 2TU Darmstadt; 3Zhejiang U.
    Strengthening in HEAs has been accurately predicted in a number of HEAs using an analytic theory that assume a random alloy without solute-solute interactions. In alloys with moderate strength both solute-solute interactions in the random alloy and short-range-order (SRO) driven by solute-solute interactions could have some non-negligible impact on strengthening. Here, we present extensions of the original random theory to include solute-solute interactions and SRO, with easy-to-apply analytical models when interactions extend over only a few neighbor shells. Applications of the extended theory are made to several FCC HEAs to demonstrate quantitative effects in the range of realistic material parameters with solute-solute interactions computed via first-principles Density Functional Theory.

Chemical Effect on the Strength of Refractory High Entropy Alloys with Severe Local Lattice Distortion: Yang Tong1; Shuying Chen1; Fanchao Meng1; Peter Liaw2; Liang Jiang1; 1Yantai University; 2University of Tennessee-Knoxville
    Refractory high entropy alloys (RHEAs) have diverse local atomic environments caused by the large difference of chemistry and atomic size among their constituents including 3d, 4d and even 5d elements. The large chemical and atomic size difference in RHEAs can significantly improve their strength. Many studies focus on the design of high strength RHEA by exploiting local lattice distortion effect induced by atomic size difference while less attention has been paid to the ruling impact of chemical difference. To demonstrate the dominant effect of chemical difference in solid solution strengthening, we examine both the atomic size and chemical effects on strength in the RHEAs with severe local lattice distortion.

Compositionally Complicated Titanium Rich Alloy for Biomedical Application: Poulami Bhattacharjee1; Ren Chung2; Hung Yen1; 1National Taiwan University; 2National Taipei University of Technology
    This study investigates the mechanical behavior of a high entropy alloy (HEA): Ti5Nb1Ta1Zr1Mo1Sn1 in as-cast, annealed, and further heat-treated states. The microstructural characterization and compositional analysis were done using scanning electron microscope, electron backscattering diffraction, and X-ray diffraction. It was found that microstructure exhibited elemental fluctuation within the body-centered cubic matrix and formation of Sn3Zr5 intermetallic along the grain boundaries. Such microstructure achieved a high UTS of more than 1.7 GPa, a hardness of more than 460 HV and a ductility of about 09-11%. This can be a low-cost and high-performance alloy for biomedical applications.

Heterogeneous Ultrafine Grain Formation by Severe Plastic Deformation in CrMnFeCoNi HEAs: Koichi Tsuchiya1; Jangho Yi1; Sangmin Lee1; Je In Lee2; 1National Institute for Materials Science; 2Pusan National University
    Process of grain refinement by severe plastic deformation by high-pressure torsion (HPT) was investigated for Cr20Mn20Fe20Co40-xNix (x=0~40). Samples with 0~5atl%Ni are composed of HCP and FCC phases after the heat treatment, while others are in the FCC single phase state.For the 15~20Ni alloys, HPT led to a drastic increase in micro-Vickers Hardness (Hv). This can be attributed to rapid progress of grain refinement.BSD-SEM observations revealed that initial formation of lamellar structures of about 100 nm width separated by nanotwins. This accelerates an increase in dislocation density and led to formation of equiaxed nanograins (~50 nm) by continuous dynamic recrystallization. Tensile properties of HPT deformed samples were studied. Large tensile elongation, typical of FCC HEAs, was much reduced by nanograin formation. But Ni10 and Ni 15 after HPT of 1/2 rotation still exhibited about 10% total elongation with high the tensile strength up to 1.5 GPa.

Hydrogen Storage Characteristics of Multi-principal Element Alloys and Composites: Jurgen Eckert1; 1Erich Schmid Institute of Materials Science
    This talk explores the hydrogen storage performance of multi-principal element alloys including high entropy alloys, single- and multiphase mixtures and composites synthesized using rapid quenching or powder metallurgy for tuning phase formation and microstructure development. The role of composition and nanostructuring will be critically assessed with respect to structural stability and evolution of hydrogen storage characteristics upon electrochemical and gas-solid reactions. Examples for composition fine-tuning and the role of grain boundaries on the storable amount of hydrogen and the uptake and release kinetics will be discussed and analyzed as ways to control the volumetric hydrogen uptake, the adsorption/desorption behavior and the tong-term cyclic stability of the material. Besides metallic systems, also examples for metal/polymer composites and membranes for hydrogen separation will be given, attempting to derive guidelines for how to tune phase formation, microstructure and properties of chemically complex multi-principal element alloys with optimized hydrogen storage properties.

Shear Instabilities of BCC Refractory High Entropy Alloys: Michael Widom1; 1Carnegie Mellon University
    Body centered cubic refractory alloys of valence 4 and 5 (the Ti and V columns of the periodic table) exhibit a variety of shear instabilities related to their electronic structure. This talk will examine the band structures leading to instabilities in the case of pure elements, then illustrate the generalization to refractory high entropy alloys through the evaluation of fully nonlinear elastic tensors.

Ultrafast Multilayer Combustion Synthesis of B2 Single Phase AlCoCrFeNi High Entropy Alloy Films Using Reactive Al/Ni Multilayer as Heat Source: Anni Wang1; Isabella Gallino2; Sascha Riegler2; Yi-Ting Lin3; Nishchay Isaac4; Yesenia Sauni Camposano4; Sebastian Matthes4; Dominik Flock4; Heiko Jacobs4; Hung-Wei Yen3; Peter Schaaf4; 1FemtoTools; 2Saarland University; 3National Taiwan University; 4TU Ilmenau
     We present here a new method to produce ultrafine single B2 phase high-entropy alloy films (HEAF) with equiatomic AlCoCrFeNi composition [1]. The method consists of stacking three multilayer thin films together, i.e., two Al/Ni films (Ni/Al units) between a CrNi/Al/CoFe (HEAF units) film. A fast scanning calorimetry (FSC) study revealed that when this triple stack Al/Ni–HEAF–Ni/Al composite is heated using flash rates in the order of 10,000 K/s a thermal explosion occurs at 700 K, forming an homogeneous single B2 phase. This reaction resembles the thermal explosion that is typically observed in electrical sparks ignited films, where the multistep phase sequence that is observed during slow annealing is kinetically suppressed altogether. A detailed kinetic analysis provided values for the activation energies of the exothermic reaction evolution.[1] A. Wang et al., Materials & Design 206 (2021)109790.

Predicting Temperature-dependent Ultimate Strengths of BCC High-entropy Alloys: Baldur Steingrimsson1; Xuesong Fan2; Michael Gao3; Peter Liaw2; 1Imagars LLC; 2University of Tennessee; 3National Energy Technology Laboratory
    This presentation expands on a bilinear log model, for predicting temperature-dependent ultimate strength of high-entropy alloys (HEAs) based on 21 compositions. We consider the break temperature introduced, Tbreak, an important design parameter. The presentation also addresses trilinear and quad-linear versions of the log model and explains why they may be appropriate for select single-crystal, Nickel-based super-alloys, such as CMSX-4, exhibiting an anomalous yield strength phenomenon. Here, the yield strength increases with temperature, resulting in a hump between low- and high-temperature regimes, due to thermally activated cross slip of dislocations from octahedral {111} planes to cubic {100} planes. This cross slip occurs with increasing ease as temperature increases. We show that most refractory HEAs contain BCC or HCP phases, with different dislocation systems. Therefore, it is unlikely that cross slip from {111} to (100) will happen in refractory HEAs. We expect the bilinear log model to suffice for most refractory HEAs.

Tunable Chemical Disorder in Concentrated Alloys: Defects and Radiation Performance: Yanwen Zhang1; Yuri Osetsky1; William Weber2; 1Oak Ridge National Laboratory; 2Department of Materials Science and Engineering, The University of Tennessee
     The development of advanced structural alloys with performance meeting the requirements of extreme environments in nuclear reactors has been long pursued. Recent success in synthesizing concentrated solid-solution alloys (CSAs) has vastly expanded the compositional space for new alloy discovery. Their wide variety of elemental diversity sets CSAs apart from traditional dilute alloys. To take advantage of property enhancement by tuning chemical disorder, research has been conducted on synergistic effects involving valence electrons and atomic-level and nanoscale inhomogeneity in CSAs composed of multiple transition metals. Knowledge of tunable chemical disorder in CSAs may advance the understanding of the substantial modifications in element-specific alloy properties that effectively mitigate radiation damage and control a material’s response in extreme environments.This work was supported as part of the Energy Dissipation to Defect Evolution (EDDE), an Energy Frontier Research Center funded by the US DOE/BES.

Thermal and Irradiation-induced Grain Growth in Nanocrystalline High-entropy Alloys: William Weber1; Yanwen Zhang2; Chinthaka Silva2; Timothy Lach2; Walker Boldman1; Philip Rack1; Li Jiang3; Lumin Wang3; Graeme Greaves4; Matheus Tunes4; Stephen Donnelly4; 1University of Tennessee; 2Oak Ridge National Laboratory; 3University of Michigan; 4University of Huddersfield
    Grain growth in nanocrystalline materials is generally thermally activated but can be driven by irradiation-induced defects and structural instabilities at lower temperatures. In nanocrystalline high-entropy alloys (HEAs), Ni20Fe20Co20Cr20Cu20 and (NiFeCoCr)97Cu3, microstructural evolution under irradiation with Ni and Au ions at room temperature has been investigated. Experimental results suggest that, similar to nanocrystalline oxides, irradiation-induced grain growth is driven by the coupling of electronic and ballistic energy dissipation that leads to faster grain growth than under thermal annealing at 300C. Grain growth follows a power law dependence that suggests irradiation-induced instabilities at grain boundaries lead to rapid local rearrangements of atoms. The additive effect of electronic and ballistic energy dissipation on grain growth opens new possibilities to modify HEAs at relative low temperatures.

Characteristics of Uniaxial Mechanical Properties of Single Crystals of FCC High- and Medium-entropy Alloys: Haruyuki Inui1; Kyosuke Kishida1; Le Li1; 1Kyoto University
    Characteristics of uniaxial mechanical properties of FCC high- and medium-entropy alloys will be described based on the results obtained from compression and tensile deformation made on single-crystal FCC high- and medium-entropy alloys of the Cr-Mn-Fe-Co-Ni quinary system and its quaternary and ternary subsystems in a temperature range of 10-1273 K. Below room temperature, the CRSS increases significantly with decreasing temperature for all these alloys, but the dulling of the temperature dependence of CRSS occurs at cryogenic temperatures for some alloys with the extent of the dulling varying from alloy to alloy. Deformation twinning occurs at low temperatures with the highest temperature for the occurrence of deformation twinning increasing with the decrease in stacking fault energy. For all these alloys, a small increase in CRSS is found at high temperatures due to the PL effect accompanied by serrated flow. Factors determining the occurrence of these characteristics will be discussed.

Corrosion of Single-phase Ni-Fe-Cr-Mo-W-X Non-equimolar Multi-principal Element Alloys: Gerald Frankel1; Anup Panindre1; Yehia Khalifa1; Christopher Taylor1; Pin Lu2; John Scully3; 1Ohio State University; 2Questek Innovations; 3University of Virginia
    Single-phase Ni-Fe-Cr-Mo-W-X (X=Ru, Mn, Al, and Cu) MPEAs were designed using an approach combining empirical knowledge about corrosion resistance and thermodynamic calculations. Each MPEA in this study contains minimum 20 at.% Cr. The MPEA that contains 13 at.% Ru exhibits excellent resistance to general as well as localized corrosion, even in Cl-environments as harsh as 6 M HCl. Ruthenium is believed to play a key role in conferring passivity to this alloy. Five more MPEAs were created by substituting Ru with commodity elements such as Mn, Al, and Cu. Each Ru-free alloy was found to resist localized corrosion at ambient temperature. Despite forming oxide films of similar thickness and quality as evaluated using single-frequency impedance methods, X-ray photoelectron spectroscopy of the passivated surface revealed constituent elements to dissolve in a non-congruent fashion. Unlike the Ru-containing MPEA, exclusive Cr enrichment was not evident in their passive films.

Deformation Behavior of a Multicomponent L21 Heusler Alloy: Rui Feng1; Chuan Zhang2; Michael Gao3; Zongrui Pei3; Yan Chen1; Michael Widom4; Ke An1; Peter Liaw5; 1Oak Ridge National Laboratory; 2Computherm, LLC; 3National Energy Technology Laboratory; 4Carnegie Mellon University; 5The University of Tennessee, Knoxville
    Ordered intermetallic structures consist of two or more metals bonded with specific stoichiometries, which have attractive high-temperature properties because of the strong atomic bonds. However, such strong directional bonds also cause brittleness at room temperature due to an insufficient number of slip systems. The concept of high-entropy alloys (HEAs) opens up a new avenue to tune intermetallic compounds’ intrinsic characteristics to pursue outperforming properties. Nevertheless, the understanding of the deformation behavior of the multicomponent intermetallic compounds is still scarce. In this study, a single-phase multicomponent L21 Heusler alloy is designed based on the Al-Cr-Fe-Mn-Ti system, whose mechanical deformation behavior is studied by in-situ neutron diffraction and transmission-electron microscopy. The plastic deformation behavior of this Heusler alloy is fundamentally understood by the observed dislocation slips and the diffraction line-profile analysis. The present work can offer insights into the design of high-performance multicomponent ordered intermetallic alloys and related composites.

Development of a High Entropy Alloy Alx(CoCrCuFeNi)1-x for Diverse Security Applications: Daniel Butcher1; Jonathan Cullen1; Neil Barron2; Shahin Mehraban1; Monique Calvo-Dahlborg1; Stephen Brown1; Nicholas Lavery1; 1Swansea University; 2Zeal Innovation Ltd
     High Entropy Alloys are a new and exciting branch of metallurgy known for corrosion resistance and high hardness properties of interest in demanding and premium high-security applications, where the hardest (>700HV) and strongest (tensile UTS> 1200 MPa) materials are required, whilst also being lightweight (<7 g/cc) in transport applications. These properties are normally found from precipitation hardened, maraging or tool steels with high tensile strengths and ductility (7-10% uniform elongation).The HEA system Alx(CoCrCuFeNi)1-x holds the promise of high hardness and relatively low density, but only compressive properties have been examined because of the predominantly BCC phases in the higher Al compositions. For a range of both equimolar and non-equimolar variants of this HEA, microstructure, composition and properties are evaluated via XRD, SEM/EDS, hardness testing and high throughput punch, to see if there is a balance of properties which can match those of the benchmark steels.

Mixed Metal Oxide Reduction: A Novel Ceramic Derived Processing Route for Multi-principal Element Alloys: Animesh Kundu1; Helen Chan1; Madison Gianelle1; 1Lehigh Univ
    Multi-Principal Element Alloys (MPEAs) are an emerging class of materials with unique physical characteristics and functional properties. To date, the most widely used processing methods for MPEAs are arc melting and mechanical alloying. The study explores the feasibility of a novel process for bulk MPEAs, namely mixed metal oxide reduction (MOR). In this process individual metal oxides are mixed and reduced to metallic alloys under appropriate processing conditions. The process has been utilized to produce several MPEAs including Cantor alloy, as well as MPEA-ceramic composites with unique microstructures. The microstructures are characterized by x-ray diffraction, SEM and analytical electron microscopy tools such as EBSD and EPMA. The results indicate that a complex interplay between thermodynamics and kinetics dictates the formation of the MPEAs in the MOR process. The thermo-kinetics of the reduction process and its concomitant effect on the microstructure and properties will be discussed.

Alloy Design, Microstructure Analysis, Mechanical Testing and Weldability of a Novel CoCuFeMnNi-based High Entropy Alloy: Jacopo Fiocchi1; Carlo Biffi2; Mauro Coduri3; Ali Mostaed4; Luca Patriarca5; Maurizio Vedani5; Ausonio Tuissi2; Riccardo Casati5; 1Politecnico di Milano / CNR ICMATE; 2CNR ICMATE; 3University of Pavia; 4University of Oxford; 5Politecnico di Milano
    High entropy alloys are a novel class of metallic materials, which open unpreceded room for the design of new alloys. Herein, equiatomic CoCuFeMnNi alloy was modified through the addition of alloying elements to favour the precipitation of strengthening second phases during ageing treatment. The alloy was designed with a mechanistic approach aided by CALPHAD simulations. The alloy was then cast, cold rolled and eventually subjected to heat treatments. Microstructural analysis was performed by synchrotron X-ray diffraction and transmission electron microscopy. It revealed a microstructure consisting of FCC grains free of second phases after solution treatment. Ageing led to the spinodal decomposition of the solid solution and different types of coherent precipitates. Fracture toughness and tensile behaviour of the alloys were investigated at room and cryogenic temperatures. Laser processing of thin sheets was finally performed to evaluate the alloy weldability and the effect of the high cooling rates on microstructure.

Fabrication and Investigation of Lightweight Porous Titanium-containing Medium and High-entropy Alloys by Freeze Casting: Kuan-Cheng Lai1; Ko-Kai Tseng1; Jien-Wei Yeh1; Po-Yu Chen1; 1National Tsing Hua University
    The freeze-casting technique can manufacture anisotropic, interconnected porous materials. In this study, porous TiNbCr medium-entropy alloy and Al0.5CoCrFeNi2Ti0.5 high-entropy alloy were developed by freeze-casting with gas-atomized powders. The particles were spherical in shape with an average diameter of ~10 μm. Our study focused on how processing parameters, such as cooling rate, sintering temperature, and solid loading, could affect microstructure and mechanical behaviors of the alloys. We sintered the porous alloys under hydrogen atmosphere to prevent oxidation. By applying 5℃/min freezing rate and 20 vol% solid loading, porous Ti-containing alloys were fabricated with aligned porous microstructure. The volume shrinkage, scaffold density, and porosity were in the range of 30-36%, 1.5-2 g/cm3 and 65-71%, respectively. Compressive mechanical properties were improved with increasing sintering temperature and duration. The freeze-casted alloys exhibited anisotropic mechanical performance compared to typical metal foams. Integrating freeze-casting with gas-atomization, porous alloys can be fabricated and applied in various fields.

Hydrogen-enhanced Ductility in CoCrFeMnNi High-entropy Alloy Additively Manufactured by Selective Laser Melting: Yi Ting Lin1; Zhiguang Zhu2; Xianghai An3; Mui Ling Sharon Nai2; Hung Wei Yen1; 1National Taiwan University; 2Singapore Institute of Manufacturing Technology; 3The University of Sydney
    In this work, the susceptibility of hydrogen embrittlement of the CoCrFeMnNi high-entropy alloy (HEA) additively manufactured by selective laser melting (SLM) was investigated. Extensive microstructural analysis and thermal desorption analyses were conducted to study the hydrogen trapping behavior, which revealed the high hydrogen capacity due to the complex hierarchical microstructures. Interestingly, the SLM-built CoCrFeMnNi exhibit a higher total elongation after cathodic hydrogen charging. The results show that the excellent resistance to hydrogen embrittlement was due to the high hydrogen content and more formations of deformation twins.