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High Entropy Materials: Concentrated Solid Solutions, Intermetallics, Ceramics, Functional Materials and Beyond II: On-Demand Oral Presentations
Sponsored by: TMS Alloy Phases Committee, TMS Mechanical Behavior of Materials Committee
Program Organizers: Michael Gao, National Energy Technology Laboratory; Xingbo Liu, West Virginia University; Peter Liaw, University of Tennessee; Jian Luo, University of California, San Diego; Yiquan Wu, Alfred University; Yu Zhong, Worcester Polytechnic Institute; Mitra Taheri, Johns Hopkins University; Amy Clarke, Los Alamos National Laboratory

Friday 8:00 AM
October 22, 2021
Room: On-Demand Room 7
Location: MS&T On Demand

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Keynote
Recreate New Life of the Periodic Table: High-entropy Alloys: Jien-Wei Yeh¹; ¹National Tsing Hua University
    Since ancient times, there has been an unbreakable myth in the manufacture of materials: it is believed that the more kinds of alloying elements are added in high proportions, the more difficult and brittle it is to alloy them together. To break the myth, “high-entropy alloys” was proposed in 2004 and defined as having at least five major elements. The name emphasized the high entropy effect which enhances multi-principal elements in a composition to form solid solutions. Severe lattice distortion, sluggish diffusion and cocktail effects also accompany high-entropy alloys in affecting microstructure and properties. Now, the high-entropy papers are growing exponentially and 5,900 in number till the end of 2020. The elemental periodic table has a new life under this composition concept providing unlimited compositions and properties. This talk briefly summarizes the four core effects and describes the current technology of high-entropy materials in the industries.

Invited
Oxidation Behavior of Concentrated Refractory Alloys: Todd Butler¹; Tinuade Daboiku¹; Oleg Senkov¹; ¹Air Force Research Laboratory
    Concentrated refractory alloys demonstrate great potential for use in high-temperature, structural applications due to their reported high-temperature strength, potential for density reduction, and environmental resistance, amongst other favorable material properties. This includes alloys that are categorized as high-entropy alloys (e.g. HEAs), as well as, alloys consisting of fewer than five base elements, albeit concentrated in nature (e.g. complex concentrated alloys, CCAs). With respect to oxidation, the compositional complexity of these alloys enables inherent complex oxide formation, offering sluggish oxidation kinetics that are not readily accessible in conventional, dilute refractory alloys. However, the fundamental mechanisms governing this behavior, and the ability to synergistically couple environmental resistance with other salient properties (e.g. mechanical strength), are not well understood. This talk will outline recent developments in the community’s understanding of this space. Existing knowledge gaps and key opportunities will be discussed relative to conventional refractory alloys.

Invited
The Role of Composition and Static Displacements on Phase Stability of BCC High Entropy Alloys: German Samolyuk¹; Yuri Osetsky¹; Malcolm Stocks¹; James Morris²; ¹Oak Ridge National Lab; ²Ames Laboratory
     A primary focus on high entropy alloy research has been identifying compositions that form solid solutions. For BCC solid solutions, there is significant attention to the role of transformation-induced plasticity, as a mechanism that may promote ductility. We discuss how composition and local distortions affect phase stability. We demonstrate that in BCC structures, the static displacements are both large and strongly composition dependent. In cases such as HfNbTiZr, we show that large displacements are crucial for understanding the observed stability of the BCC phase at low temperatures, implying a non-entropic contribution to the phase stability. We discuss the origin of this, and the connection to transformation pathways in these materials.Work supported by Department of Energy’s Office of Science, Basic Energy Science, through the Energy Dissipation to Defect Evolution EFRC (GDS, YO and GMS), and through the Materials Science and Engineering Division (JRM).

Invited
Designing High-entropy Intermetallics: Machine Learning Models and Validation: Joseph Poon¹; Jie Qi¹; ¹University of Virginia
    Due to the exponential growth in compositions, there exists the fundamental challenge of exploiting the enormous unique opportunities for designing high-entropy alloys (HEAs). Although the use of data-driven methods, such as supervised machine learning (ML), in HEA research, has achieved various degrees of success in predicting solid-solution phases, there exist inherent limitations such as available datasets and the effectiveness of selected features. High-entropy intermetallic phases, which exist either as composites or single-phase alloys, have the potential to deliver superior structural and functional properties. Nevertheless, the prediction of high-entropy intermetallics(HEI) raises yet another level of challenge. In this talk, we will present various ML models that utilize a combination of data-guided (phenomenological) and physics-based (adaptive) features, complemented with features engineering and experimental results, to explore the complex compositional landscape of HEI. We focus on two types of intermetallics namely Heusler and B2 ordered body-centered cubic phases.

Invited
Enhanced Oxidation Resistance of (Mo95W5)85Ta10(TiZr)5 Refractory Metal Multi-principal Element Alloy Up to 1300°C: Ranran Su¹; Hongliang Zhang²; Gaoyuan Ouyang³; Longfei Liu²; Jun Cui³; Duane Johnson³; John Perepezko²; ¹University of Wisconsin-Madison; ²Department of Materials Science and Engineering, University of Wisconsin-Madison; ³Ames Laboratory, U.S. Department of Energy at Iowa State University
    Refractory-metal-based alloys are a potential replacement of current nickel-based superalloys due to their excellent mechanical strength at extremely high temperatures. However, severe oxidation in a high-temperature working environment limits their application. A two-step coating process (including a Mo precoating and a Si-B pack cementation) was applied to an innovative refractory multi-principal element alloy (MPEA) (Mo95W5)85Ta10(TiZr)5. The coating is composed of an aluminoborosilica glass layer on top of a MPEA-Si-B multilayered structure. The coating effectively protects the MPEA from oxidation in high-temperature environments, as demonstrated by phase-stable operation at 10-20% higher temperatures over state-of-the-art systems without any forced-cooling system.

Invited
Ultrahigh-strength and Ductile High-entropy Alloys with Coherent Nano-lamellar Architectures: Zengbao Jiao¹; ¹The Hong Kong Polytechnic University
    Nano-lamellar materials with ultrahigh strengths and unusual physical properties are of technological importance for structural applications. However, these materials generally suffer from low tensile ductility, which severely limits their practical utility. In this talk, we show that markedly enhanced tensile ductility can be achieved in coherent nano-lamellar high-entropy alloys, which exhibit an unprecedented combination of over 2 GPa yield strength and 16% uniform tensile ductility. The ultrahigh strength originates mainly from the lamellar boundary strengthening, whereas the large ductility correlates to a progressive work-hardening mechanism regulated by the unique nano-lamellar architecture. The coherent lamellar boundaries facilitate the dislocation transmission, which eliminates the stress concentrations at the boundaries. Meanwhile, deformation-induced hierarchical stacking-fault networks and associated high-density Lomer-Cottrell locks enhance the work hardening response, leading to unusually large tensile ductilities. The coherent nano-lamellar strategy can potentially be applied to other alloys and open new avenues for designing ultrastrong-yet-ductile materials for technological applications.

Invited
Exploring the Chemical and Structural Phase Space of High Entropy Alloys with Ab Initio Calculations and Machine Learning Potentials: Fritz Koermann¹; ¹Tu Delft
    Progress in combining ab initio simulations, machine learning interatomic potentials and active learning algorithms are discussed enabling the exploration of structural and chemical stability as well as the elastic properties of high entropy alloys. The application of on-lattice machine learning potentials with Monte Carlo simulations for short-range order are discussed on several examples [1]. The structural stability is presented for TiZrNbHfTa alloys and it is found that atomic relaxations are crucial to accurately determine the structural bcc-hcp phase stability [2]. To distinguish the bcc and omega phase in these complex alloys a structural descriptor is proposed [2]. Utilizing this descriptor in combination with machine learning techniques and molecular dynamics simulations, the temperature-dependent structural-stability and elastic properties for TiZrHfTa alloys are presented, revealing strong intrinsic correlations.[1] npj Comp. Mat. 5, 55 (2019). [2] npj Comp. Mat. 7, 34 (2021).

Invited
Local Ordering and Defect Evolution in Body-centered Cubic (BCC) Multi-principal Element Alloys: Shijun Zhao¹; ¹City University of Hong Kong
    The recent development of high-entropy alloys (HEAs) has opened a new avenue for alloy design by incorporating multiple principal elements into a simple crystal lattice. Compared to face-centered cubic (FCC) HEAs, the studies on the body-centered cubic (BCC) HEAs still in their infancy. In this study, we combined first-principles calculations with Monte Carlo simulations to study the trend of elemental arrangement in typical BCC multi-principal element alloys (MPEAs), including CrFeV, HfNbZr, TaVW, NbTaV, and TaTiV. Our results demonstrated that all these MPEAs might develop a certain degree of SRO, depending on the mixing properties of different element pairs. The results are in good agreement with a modified quasi-chemical model. We further studied defect accumulation properties in several representative BCC MPEAs, including TaTiV and TaTiVNb. We show that these BCC MPEAs strongly suppress the development of large dislocation loops, rendering them good candidates materials for future nuclear applications.

Invited
FeNiMnAl(Cr) Multi-principal Component Alloys: Ian Baker¹; ¹Dartmouth College
    This presentation will describe four different types of microstructures in FeNiMnAl(Cr) multi-principal component alloys along with their corresponding mechanical properties: 1) ultrafine (5-50 nm) spinodal microstructures present in Fe₃₀Ni₂₀Mn₂₀Al₃₀, Fe₂₅Ni₂₅Mn₂₀Al₃₀ and Fe₃₅Ni₁₅Mn₂₅Al₂₅, which consist of (Fe, Mn)-rich B2-ordered (ordered b.c.c.) and (Ni, Al)-rich L21-ordered (Heusler) phases, and in Fe₃₀Ni₂₀Mn₂₅Al₂₅, which consist of (Ni, Al)-rich B2 and (Fe, Mn)-rich b.c.c. phases, with the phases aligned along <100>; 2) fine (50-70 nm) eutectoid microstructures, present in Fe₃₀Ni₂₀Mn₃₀Al₂₀, Fe₂₅Ni₂₅Mn₃₀Al₂₀, and Fe₂₈Ni₁₈Mn₃₃Al₂₁, which consist of alternating (Fe, Mn)-rich f.c.c and (Ni, Al)-rich B2-ordered plates with an orientation relationship close to f.c.c.(002)//B2(002); f.c.c.(011)//B2(001); 3) coarser (0.5-1.5 µm) lamellar eutectic microstructures observed in alloys with a lower aluminum content, such as Fe₃₀Ni₂₀Mn₃₅Al₁₅, that consist of alternating (Fe, Mn)-rich f.c.c and (Ni, Al)-rich B2-ordered phases with a Kurdjumov-Sachs orientation relationship between the phases; and 4) single-phase (in the as-cast state) high-entropy alloys such as Fe_40.4Ni_11.3Mn_34.8Al_7.5Cr₆.

Invited
Creep Performance of Various Single Phase FCC CoCrFeNi Family of High Entropy Alloys: Kyle Rozman¹; Martin Detrois¹; Paul Jablonski¹; Michael Gao¹; Jeffery Hawk¹; ¹National Energy Technology Laboratory
    With goals to develop alloys for the next generation of advanced ultra-supercritical power turbines, the National Energy Technology Laboratory (NETL) has produced a series of CoCrFeNi single phase FCC HEAs, with Mn or Mo variants. Further efforts include high entropy (HE) superalloys where matrix entropy is maximized. NETL has produced these alloys as fully wrought plates, originating from small scale 7-10 kg ingots. Such a methodology is scalable to large production methods using a combination of vacuum induction melting and electro-slag remelting. Full-size tensile and creep specimens were produced from these ingots and tested to failure in tension or creep. NETL has accumulated over 100,000 hours (combined) of creep rupture data on these HEAs. This presentation focus on the creep properties of these CoCrFeNi family of alloys, reporting and contrasting their performance with relevant structural alloys.

Invited
Microstructure and Mechanical Properties of Hf-27Ta and Hf-21Ta-21X (X is Nb, Mo or W) Alloys: Oleg Senkov¹; Tinuade Daboiku¹; Todd Butler¹; Michael Titus²; Noah Philips³; Eric Payton¹; ¹Air Force Research Laboratory; ²Purdue University; ³ATI Specialty Alloys and Components
    The microstructure and mechanical properties of Hf-Ta-M alloys (M is Mo, Nb or W) are reported. The microstructure of Hf-27Ta consisted of coarse primary HCP particles and a monotectoidally transformed nano-lamella mixture of Ta-rich BCC and Hf-rich HCP phases. Hf-21Mo-21Ta consisted of a BCC matrix phase and HCP precipitates. Hf-21Nb-21Ta contained spherical nano-precipitates inside BCC matrix grains and two-phase BCC lamellar regions at grain boundaries. Hf-21Ta-21W had a Hf-rich HCP matrix, W-rich cubic Laves phase and monotectoidally transformed regions of Ta-rich BCC and Hf-rich HCP nano-lamellae. Hf-27Ta had yield stress of 1708 MPa at 25°C. Additions of Nb, Mo or W decreased the 25°C yield stress to 832 MPa, 1496 MPa or 1475 MPa, respectively. Hf-21Mo-21Ta was the strongest alloy at T ≥ 1000°C. Its yield stress at 1000°C, 1200°C and 1400°C was 943 MPa, 421 MPa and 146 MPa, respectively. Relationships between the microstructure and mechanical properties are discussed.

Invited
Tuning Mechanical Metastability in FeMnCo Medium Entropy Alloys: S.L. Wei¹; M. Xu¹; James LeBeau¹; C. Tasan¹; ¹Massachusetts Institute of Technology
    In this talk, the compositional dependency of face-centered cubic (FCC) to hexagonal close-packed (HCP) martensitic transformation in FeMnCo medium entropy alloys (MEAs) will be reported, and insights into the underlying transformation mechanisms will be discussed. To this end, the designed MEAs with the same Fe-to-Mn ratio and their phase stability will be presented. The investigations demonstrate that higher Co contents facilitate the FCC-HCP transformation kinetics. In situ electron backscatter diffraction (EBSD) studies reveal an FCC-HCP-(new)FCC transformation chain and its underlying atomistic mechanisms are directly explored via aberration-corrected scanning transmission electron microscopy.

Invited
Ab Initio Modeling on the Elastic Properties of Al-Co-Cr-Fe-Ni High Entropy Alloys: A Case Study with FCC Phase: Songge Yang¹; Yu Zhong¹; ¹Worcester Polytechnic Institute
    The Al-Co-Cr-Fe-Ni system has been one of the most thoroughly studied systems in high entropy alloys (HEAs) due to their promising mechanical properties. However, the prediction of mechanical properties in this system with a full composition range could be challenging purely based on experiments. In the current study, the high-throughput ab initio modeling combined with the machine learning (ML) approach is used to predict the elastic properties of the quinary FCC Al-Co-Cr-Fe-Ni HEA single crystals by using the special quasi-random structure (SQS) approach. The predictions will start with pure elements of the Al-Co-Cr-Fe-Ni system and will be continued with binaries, ternaries, and quaternary compositions. More than 100 compositions were simulated. After that, the elastic property database of the FCC phase in this system will be contoured with composition space.

Invited
Theories for Predicting Simple Solid Solution High-entropy Alloys: Classification, Accuracy, and Important Factors Impacting Accuracy: Jian-Hong Li¹; Ming-Hung Tsai¹; An-Chen Fan¹; ¹National Chung Hsing University
    In this work, representative theories for predicting simple solid solution high-entropy alloys (HEAs) are reviewed. The models are first classified into two categories - parameter based and free-energy based, according to their core strategy. Then, one hundred distinct HEAs are used to benchmark the accuracy and the degree of unbalance of the models. Based on careful analysis of the results, five factors that impact the accuracy of models are pointed out and discussed. These include two global factors and three alloy-specific factors. Finally, future directions to better assess these theories and to develop more accurate models are suggested.


Thermal Conductivity Reduction in (Zr_0.25Ta_0.25Nb_0.25Ti_0.25)C High Entropy Carbide from Extrinsic Lattice Defects: Cody Dennett¹; Fei Wang²; Bai Cui²; ¹Idaho National Laboratory; ²University of Nebraska-Lincoln
    Thermal transport in high-entropy ceramics (HECs) is dramatically affected by the chemical disorder which stabilizes simple phases. However, with significant lattice contributions to thermal conductivity, structural defects should also play a meaningful role in the resulting material properties, though available experimental data is scarce. Here, we directly measurement thermal transport in bulk (Zr_0.25Ta_0.25Nb_0.25Ti_0.25)C which has been subjected to 3 MeV Zr ion beam irradiation at several temperatures to extrinsically impose lattice defects. The thermal conductivity of the defected layer is extracted using a spatial domain thermoreflectance (SDTR) technique and multi-layer thermal modeling. The thermal conductivity of specimens exposed to 8e15 ions/cm² is found to drop by ~15% at the lowest exposure temperature. A simple Debye approach to model lattice conductivity is combined with TEM-measured dislocation loop characteristics to quantify the excess reduction resulting from point defects. This work provides a foundation for additional routes to engineer low-conductivity, environmentally stable HECs.


Interstitial Induced Transformations in Nb-Ti Alloys: Ravit Silverstein¹; Anirudh Natarajan¹; Raphaële Clément¹; Anton Van der Ven¹; Carlos Levi¹; ¹University of California, Santa Barbara
    This study addresses the effect of incorporating dilute amounts of oxygen (<1at%) in concentrated Nb-Ti bcc solid solutions as a baseline for subsequent studies in higher order MPEs. Alloys were splat quenched and some were either encapsulated and exposed to 16O infusion, or crushed into powders using a hydriding/dehydriding method and exposed to 17O for NMR studies. The study shows that oxygen incorporation induces a miscibility gap with potential for spinodal decomposition around the equiatomic composition. A dominant transformation mechanism for the Ti-rich phase from bcc to hcp involves a Burgers shuffle along (110) planes. For powders generated through hydriding/ dehydriding there is an alternate path generating omega phase. The transformation paths and resulting microstructures are discussed.


A Novel Soft-magnetic Single-phase B2-ordered Multi-principal Element Alloy: Youxiong Ye¹; Scott Lish¹; Liubin Xu²; Markus Wittmann²; Haixuan Xu²; Ian Baker¹; ¹Dartmouth College; ²Department of Materials Science and Engineering
    This presentation will discuss the microstructure, and magnetic and mechanical properties of a novel soft-magnetic single-phase B2-structured Fe₃₀Co₄₀Mn₁₅Al₁₅ multi-principal element alloy (MPEA). The MPEA has a high saturation magnetization of ~156 Am²/kg, a low coercivity of ~207 A/m, and a high Curie temperature of ~1137 K, which are superior to those previously reported for soft magnetic MPEAs. The alloy exhibited high thermal stability in terms of microstructure, mechanical and magnetic behavior upon long time annealing at 873 K. The sublattice site occupancy of the constituent elements was determined using the TEM-based technique ALCHEMI, and it was found that the Al tended to reside on one site, whereas the other elements partitioned between the two sites of the AB-type B2 structure. Density functional theory calculations revealed that Co, Fe, and Mn showed ferromagnetic behavior, while Al exhibited non-ferromagnetism. The excellent soft magnetic properties were retained at up to 973 K.


Deformation of Refractory Multi-principal Element Alloy Nanowires: Shuozhi Xu¹; Yanqing Su²; ¹University of California, Santa Barbara; ²Utah State University
    Multi-principal element alloys (MPEAs) are alloys that form solid solution phases and consist of three or more principal metallic elements. They are considered to have intermediate structural and chemical complexities between single-element regular metals and multi-element disordered metallic glasses. Due to their unique microstructures and chemical compositions, MPEAs exhibit excellent mechanical properties such as high strength at elevated temperatures and excellent ductility at low temperatures. Among all MPEAs, refractory MPEAs mainly consist of refractory metals, and some of them can retain reasonably high strengths at 1600 oC. Here, atomistic simulations are performed to study the tensile and compressive loadings of a series of refractory MPEA nanowires. The MPEAs considered in this work include ternaries, quaternaries, and quinaries, differing in chemical compositions. Results demonstrate the relation between the strengthening and lattice distortion of MPEAs. The origin of this relationship is discussed.


Understanding the Nature of Passivation Film of a TRIP Fe39Mn20Co20Cr15Si5Al1 (at.%) High Entropy Alloy in 3.5 wt.% NaCl Solution: Pranshul Varshney¹; Nilesh Kumar¹; ¹University of Alabama-Tusaloosa
    The nature of passive films affects the corrosion properties of alloys. The corrosion susceptibility of an alloy may undermine the structural integrity of any engineering component. The advanced materials such as high entropy alloys (HEAs) are being explored for a wide range of applications that requires property evaluation under different environments including corrosive atmosphere. The present study unveils the passivation film behavior of a transformation-induced-plasticity (TRIP) Fe39Mn20Co20Cr15Si5Al1 (at.%) HEA in 3.5 wt.% NaCl solution at room temperature. The passivation film characterization has been conducted using advanced analytical tools including electrochemical impedance spectroscopy and X-ray photoelectron spectroscopy before and after the corrosion test. The preliminary results show excellent passivation film characteristics towards uniform corrosion but susceptibility towards pitting corrosion. The passivation film parameters showed dependence on anodic potential. Further analysis of the passivation film including identification of corrosion product(s) and oxides is underway that will be discussed during presentation.

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