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Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities

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A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: closed (31 December 2019) | Viewed by 74925

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Dr. Sundeep Mukherjee

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Department of Materials Science and Engineering, University of North Texas, 3940 N. Elm Street, Denton, TX 76203, USA
Interests: metallic glasses; high entropy alloys; advanced manufacturing; electrochemistry and corrosion; multi-scale mechanical behavior
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue aims to present recent developments and future opportunities related to the topic of complex concentrated and high entropy alloys from fundamental aspects to various applications. Conventional structural alloys are single principal element systems with multi-phase microstructures. In that regard, complex concentrated alloys (CCAs), with multiple principal elements, represent a new paradigm in alloy design by focusing on the central region of a multi-component phase space rather than the edges. High configurational entropy leads to single-phase solid solutions in a certain subset of these multi-principal element systems, which have been termed as high entropy alloys (HEAs). However, the focus on a single-phase microstructure severely limits performance in real-world engineering applications. CCAs retain the “high entropy” nature of the parent matrix and add complex precipitates containing multiple elements on their respective sub-lattices as strengtheners. The core effects of high configurational entropy, lattice distortion and sluggish diffusion lead to a gamut of attractive properties including high strength-ductility combination, resistance to oxidation, corrosion/wear resistance, and interesting magnetic properties. For this Special Issue, contributions are welcome from experimentalists, theorists, and computational scientists in this field.

Specific topics of interest include (but are not limited to):

Thermodynamics, kinetics, and phase transformation in multi-phase CCAs
Mechanical behavior and deformation mechanisms
Microstructure evolution as a function of processing
Tribology, corrosion and oxidation behavior
Magnetic and magneto-caloric properties
Irradiation effects
High strain-rate deformation behavior
Simulation and modeling including DFT, MD, Phase-field, and CALPHAD

Prof. Dr. Sundeep Mukherjee
Guest Editor

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Keywords

Complex Concentrated Alloys
High Entropy Alloys
Alloy Design
Mechanical Behavior
Magnetic Properties
Irradiation Effects

Published Papers (14 papers)

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Editorial

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3 pages, 149 KiB

Open AccessEditorial

Complex Concentrated Alloys (CCAs)—Current Understanding and Future Opportunities

by Sundeep Mukherjee

Metals 2020, 10(9), 1253; https://doi.org/10.3390/met10091253 - 17 Sep 2020

Cited by 6 | Viewed by 2480

Abstract

Complex concentrated alloys with multiple principal elements represent a new paradigm in alloy design by focusing on the central region of a multi-component phase space and show a promising range of properties unachievable in conventional alloys [...] Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

Research

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12 pages, 7170 KiB

Open AccessArticle

High-Temperature Nano-Indentation Creep Behavior of Multi-Principal Element Alloys under Static and Dynamic Loads

by Maryam Sadeghilaridjani and Sundeep Mukherjee

Metals 2020, 10(2), 250; https://doi.org/10.3390/met10020250 - 13 Feb 2020

Cited by 14 | Viewed by 3479

Abstract

Creep is a serious concern reducing the efficiency and service life of components in various structural applications. Multi-principal element alloys are attractive as a new generation of structural materials due to their desirable elevated temperature mechanical properties. Here, time-dependent plastic deformation behavior of two multi-principal element alloys, CoCrNi and CoCrFeMnNi, was investigated using nano-indentation technique over the temperature range of 298 K to 573 K under static and dynamic loads with applied load up to 1000 mN. The stress exponent was determined to be in the range of 15 to 135 indicating dislocation creep as the dominant mechanism. The activation volume was ~25b³ for both CoCrNi and CoCrFeMnNi alloys, which is in the range indicating dislocation glide. The stress exponent increased with increasing indentation depth due to higher density and entanglement of dislocations, and decreased with increasing temperature owing to thermally activated dislocations. The results for the two multi-principal element alloys were compared with pure Ni. CoCrNi showed the smallest creep displacement and the highest activation energy among the three systems studied indicating its superior creep resistance. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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13 pages, 6925 KiB

Open AccessArticle

Tribological Behavior of As-Cast and Aged AlCoCrFeNi_2.1 CCA

by Fevzi Kafexhiu, Bojan Podgornik and Darja Feizpour

Metals 2020, 10(2), 208; https://doi.org/10.3390/met10020208 - 01 Feb 2020

Cited by 14 | Viewed by 2914

Abstract

In the present study, wear behavior as a function of aging time was evaluated for the AlCoCrFeNi_2.1 eutectic complex, concentrated alloy (CCA) consisting of B2 (BCC), and L1₂ (FCC) lamellae in the as-cast state. By aging the material at 800 °C up to 500 h, precipitation of a fine, evenly dispersed micro-phase inside the L1₂ takes place. From 500 h to 1000 h of aging, precipitates coarsen by the Ostwald ripening mechanism. Reciprocating wear tests were characterized by a prevailing abrasive wear mechanism, while adhesive and delamination wear components change with aging conditions. The L1₂ phase with lower hardness in the as-cast material preferentially deformed during the wear test, which was not the case after aging the material, i.e., with the presence of precipitates. Aging-induced changes show a similar trend for the coefficient of friction and L1₂ + precipitates phase fraction, whereas changes in specific wear rate are in a good agreement with changes in B2 phase fraction. In general, aging the AlCoCrFeNi_2.1 CCA at 800 °C up to 500 h decreases its coefficient of friction due to reduced adhesive wear component and enhances its wear performance through precipitation strengthening. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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14 pages, 6717 KiB

Open AccessArticle

Microstructure and Properties of High-Entropy Al_xCoCrFe_2.7MoNi Alloy Coatings Prepared by Laser Cladding

by Minghong Sha, Chuntang Jia, Jun Qiao, Wenqiang Feng, Xingang Ai, Yu-An Jing, Minggang Shen and Shengli Li

Metals 2019, 9(12), 1243; https://doi.org/10.3390/met9121243 - 20 Nov 2019

Cited by 18 | Viewed by 2824

Abstract

High-entropy Al_xCoCrFe_2.7MoNi (x = 0, 0.5, 1.0, 1.5, 2.0) alloy coatings were prepared on pure iron by laser cladding. The effects of Al content on the microstructure, hardness, wear resistance and corrosion resistance of the coatings were studied. The results showed that the crystal phases of the Al_xCoCrFe_2.7MoNi coatings changed from Mo-rich BCC1 + FCC to (Al, Ni)-rich BCC2 + Mo-rich BCC1 when x increased from 0 to 0.5, and the phase changed to an (Al, Ni)-rich BCC2 + (Mo, Cr)-rich σ phase as x increased further. The hardness of the coatings increased as the Al content increased. The Al_2.0CoCrFe_2.7MoNi coating exhibit best wear resistance. Addition of Al increased the corrosion potential in a 3.5 wt.% NaCl solution, and the coating with x = 1.0 exhibited the highest corrosion resistance. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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12 pages, 7715 KiB

Open AccessArticle

Corrosion Behavior of Selectively Laser Melted CoCrFeMnNi High Entropy Alloy

by Jie Ren, Chaitanya Mahajan, Liang Liu, David Follette, Wen Chen and Sundeep Mukherjee

Metals 2019, 9(10), 1029; https://doi.org/10.3390/met9101029 - 23 Sep 2019

Cited by 43 | Viewed by 5362

Abstract

CoCrFeMnNi high entropy alloys (HEAs) were additively manufactured (AM) by laser powder bed fusion and their corrosion resistance in 3.5 wt% NaCl solution was studied by potentiodynamic polarization and electrochemical impedance spectroscopy tests. A systematic study of AM CoCrFeMnNi HEAs’ porosity under a wide range of laser processing parameters was conducted and a processing map was constructed to identify the optimal laser processing window for CoCrFeMnNi HEAs. The near fully dense AM CoCrFeMnNi HEAs exhibit a unique non-equilibrium microstructure consisting of tortuous grain boundaries, sub-grain cellular structures, columnar dendrites, associated with some processing defects such as micro-pores. Compared with conventional as-cast counterpart, the AM CoCrFeMnNi HEAs showed higher pitting resistance (ΔE) and greater polarization resistance (R_p). The superior corrosion resistance of AM CoCrFeMnNi HEAs may be attributed to the homogeneous elemental distribution and lower density of micro-pores. Our study widens the toolbox to manufacture HEAs with exceptional corrosion resistance by additive manufacturing. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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12 pages, 6631 KiB

Open AccessArticle

Gradient Distribution of Microstructures and Mechanical Properties in a FeCoCrNiMo High-Entropy Alloy during Spark Plasma Sintering

by Mingyang Zhang, Yingbo Peng, Wei Zhang, Yong Liu, Li Wang, Songhao Hu and Yang Hu

Metals 2019, 9(3), 351; https://doi.org/10.3390/met9030351 - 19 Mar 2019

Cited by 8 | Viewed by 3009

Abstract

A novel graded material of a high-entropy alloy (HEA) FeCoCrNiMo was fabricated by spark plasma sintering (SPS) processing. After SPS, the HEA specimens consisted of a single face-centred cubic (FCC) phase in the center, but dual FCC and a tetragonal structure σ phase near the surface. Surprisingly, the sintering pressure was sufficient to influence the proportion of phases, and thus the properties of HEA samples. The hardness of the specimens sintered under the pressures of 30, 35, and 40 MPa increased gradually from 210 HV_0.2, which is the single FCC phase in the center, to the maximum value near the surface as a result of the gradual increase in the fraction of the transformed σ phase. The σ phase, being a complex hard and brittle intermetallic particle to manipulate the properties of FCC-type HEA systems, which could be influenced by pressure, indicated a major possibility for designing gradient HEA materials. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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10 pages, 3328 KiB

Open AccessArticle

Activation Volume and Energy for Dislocation Nucleation in Multi-Principal Element Alloys

by Sanghita Mridha, Maryam Sadeghilaridjani and Sundeep Mukherjee

Metals 2019, 9(2), 263; https://doi.org/10.3390/met9020263 - 23 Feb 2019

Cited by 42 | Viewed by 4984

Abstract

Incipient plasticity in multi-principal element alloys, CoCrNi, CoCrFeMnNi, and Al_0.1CoCrFeNi was evaluated by nano-indentation and compared with pure Ni. The tests were performed at a loading rate of 70 μN/s in the temperature range of 298 K to 473 K. The activation energy and activation volume were determined using a statistical approach of analyzing the “pop-in” load marking incipient plasticity. The CoCrFeMnNi and Al_0.1CoCrFeNi multi-principal element alloys showed two times higher activation volume and energy compared to CoCrNi and pure Ni, suggesting complex cooperative motion of atoms for deformation in the five component systems. The small calculated values of activation energy and activation volume indicate heterogeneous dislocation nucleation at point defects like vacancy and hot-spot. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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13 pages, 25906 KiB

Open AccessArticle

Preparation and Performance Analysis of Nb Matrix Composites Reinforced by Reactants of Nb and SiC

by Zhen Lu, Chaoqi Lan, Shaosong Jiang, Zhenhan Huang and Kaifeng Zhang

Metals 2018, 8(4), 233; https://doi.org/10.3390/met8040233 - 03 Apr 2018

Cited by 4 | Viewed by 3458

Abstract

In this paper, one kind of new composite material formed with Nb and SiC was prepared by hot pressing sintering. The influence of the addition of SiC particles on the mechanical properties at room and high temperature was analyzed. The composite material consists of three phases: Nb₂C, Nb₃Si, and Nb solid solution (Nbss). The fraction of SiC particles added in the Nb matrix was 3%, 5%, and 7%, respectively. Flexural strength, Vickers hardness, and compressive strength at room temperature were improved with the increasing of SiC content. Among them, compressive strength and fracture toughness were higher than those of Nb/Nb₅Si₃ composites. The compressive strength at high temperature of the new composites was higher than that of Nb-Si alloys, which improved with the increasing of SiC content. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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12 pages, 3890 KiB

Open AccessArticle

Slurry Erosion Behavior of Al_xCoCrFeNiTi_0.5 High-Entropy Alloy Coatings Fabricated by Laser Cladding

by Jianhua Zhao, Aibin Ma, Xiulin Ji, Jinghua Jiang and Yayun Bao

Metals 2018, 8(2), 126; https://doi.org/10.3390/met8020126 - 11 Feb 2018

Cited by 33 | Viewed by 6042

Abstract

High-entropy alloys (HEAs) have gained extensive attention due to their excellent properties and the related scientific value in the last decade. In this work, Al_xCoCrFeNiTi_0.5 HEA coatings (x: molar ratio, x = 1.0, 1.5, 2.0, and 2.5) were fabricated on Q345 steel substrate by laser-cladding process to develop a practical protection technology for fluid machines. The effect of Al content on their phase evolution, microstructure, and slurry erosion performance of the HEA coatings was studied. The Al_xCoCrFeNiTi_0.5 HEA coatings are composed of simple face-centered cubic (FCC), body-centered cubic (BCC) and their mixture phase. Slurry erosion tests were conducted on the HEA coatings with a constant velocity of 10.08 m/s and 16–40 meshs and particles at impingement angles of 15, 30, 45, 60 and 90 degrees. The effect of three parameters, namely impingement angle, sand concentration and erosion time, on the slurry erosion behavior of Al_xCoCrFeNiTi_0.5 HEA coatings was investigated. Experimental results show AlCoCrFeNiTi_0.5 HEA coating follows a ductile erosion mode and a mixed mode (neither ductile nor brittle) for Al_1.5CoCrFeNiTi_0.5 HEA coating, while Al_2.0CoCrFeNiTi_0.5 and Al_2.5CoCrFeNiTi_0.5 HEA coatings mainly exhibit brittle erosion mode. AlCoCrFeNiTi_0.5 HEA coating has good erosion resistance at all investigated impingement angles due to its high hardness, good plasticity, and low stacking fault energy (SFE). Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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Review

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72 pages, 22335 KiB

Open AccessReview

A Review of the Serrated-Flow Phenomenon and Its Role in the Deformation Behavior of High-Entropy Alloys

by Jamieson Brechtl, Shuying Chen, Chanho Lee, Yunzhu Shi, Rui Feng, Xie Xie, David Hamblin, Anne M. Coleman, Bradley Straka, Hugh Shortt, R. Jackson Spurling and Peter K. Liaw

Metals 2020, 10(8), 1101; https://doi.org/10.3390/met10081101 - 13 Aug 2020

Cited by 65 | Viewed by 9913

Abstract

High-entropy alloys (HEAs) are a novel class of alloys that have many desirable properties. The serrated flow that occurs in high-entropy alloys during mechanical deformation is an important phenomenon since it can lead to significant changes in the microstructure of the alloy. In this article, we review the recent findings on the serration behavior in a variety of high-entropy alloys. Relationships among the serrated flow behavior, composition, microstructure, and testing condition are explored. Importantly, the mechanical-testing type (compression/tension), testing temperature, applied strain rate, and serration type for certain high-entropy alloys are summarized. The literature reveals that the serrated flow can be affected by experimental conditions such as the strain rate and test temperature. Furthermore, this type of phenomenon has been successfully modeled and analyzed, using several different types of analytical methods, including the mean-field theory formalism and the complexity-analysis technique. Importantly, the results of the analyses show that the serrated flow in HEAs consists of complex dynamical behavior. It is anticipated that this review will provide some useful and clarifying information regarding the serrated-flow mechanisms in this material system. Finally, suggestions for future research directions in this field are proposed, such as the effects of irradiation, additives (such as C and Al), the presence of nanoparticles, and twinning on the serrated flow behavior in HEAs. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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16 pages, 5028 KiB

Open AccessReview

Applications of High-Pressure Technology for High-Entropy Alloys: A Review

by Wanqing Dong, Zheng Zhou, Mengdi Zhang, Yimo Ma, Pengfei Yu, Peter K. Liaw and Gong Li

Metals 2019, 9(8), 867; https://doi.org/10.3390/met9080867 - 08 Aug 2019

Cited by 18 | Viewed by 6570

Abstract

High-entropy alloys are a new type of material developed in recent years. It breaks the traditional alloy-design conventions and has many excellent properties. High-pressure treatment is an effective means to change the structures and properties of metal materials. The pressure can effectively vary the distance and interaction between molecules or atoms, so as to change the bonding mode, and form high-pressure phases. These new material states often have different structures and characteristics, compared to untreated metal materials. At present, high-pressure technology is an effective method to prepare alloys with unique properties, and there are many techniques that can achieve high pressures. The most commonly used methods include high-pressure torsion, large cavity presses and diamond-anvil-cell presses. The materials show many unique properties under high pressures which do not exist under normal conditions, providing a new approach for the in-depth study of materials. In this paper, high-pressure (HP) technologies applied to high-entropy alloys (HEAs) are reviewed, and some possible ways to develop good properties of HEAs using HP as fabrication are introduced. Moreover, the studies of HEAs under high pressures are summarized, in order to deepen the basic understanding of HEAs under high pressures, which provides the theoretical basis for the application of high-entropy alloys. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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23 pages, 5216 KiB

Open AccessReview

A Review of Multi-Scale Computational Modeling Tools for Predicting Structures and Properties of Multi-Principal Element Alloys

by Mohsen Beyramali Kivy, Yu Hong and Mohsen Asle Zaeem

Metals 2019, 9(2), 254; https://doi.org/10.3390/met9020254 - 20 Feb 2019

Cited by 11 | Viewed by 6400

Abstract

Multi-principal element (MPE) alloys can be designed to have outstanding properties for a variety of applications. However, because of the compositional and phase complexity of these alloys, the experimental efforts in this area have often utilized trial and error tests. Consequently, computational modeling and simulations have emerged as power tools to accelerate the study and design of MPE alloys while decreasing the experimental costs. In this article, various computational modeling tools (such as density functional theory calculations and atomistic simulations) used to study the nano/microstructures and properties (such as mechanical and magnetic properties) of MPE alloys are reviewed. The advantages and limitations of these computational tools are also discussed. This study aims to assist the researchers to identify the capabilities of the state-of-the-art computational modeling and simulations for MPE alloy research. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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40 pages, 25021 KiB

Open AccessFeature PaperReview

Corrosion, Erosion and Wear Behavior of Complex Concentrated Alloys: A Review

by Aditya Ayyagari, Vahid Hasannaeimi, Harpreet Singh Grewal, Harpreet Arora and Sundeep Mukherjee

Metals 2018, 8(8), 603; https://doi.org/10.3390/met8080603 - 03 Aug 2018

Cited by 70 | Viewed by 9607

Abstract

There has been tremendous interest in recent years in a new class of multi-component metallic alloys that are referred to as high entropy alloys, or more generally, as complex concentrated alloys. These multi-principal element alloys represent a new paradigm in structural material design, where numerous desirable attributes are achieved simultaneously from multiple elements in equimolar (or near equimolar) proportions. While there are several review articles on alloy development, microstructure, mechanical behavior, and other bulk properties of these alloys, then there is a pressing need for an overview that is focused on their surface properties and surface degradation mechanisms. In this paper, we present a comprehensive view on corrosion, erosion and wear behavior of complex concentrated alloys. The effect of alloying elements, microstructure, and processing methods on the surface degradation behavior are analyzed and discussed in detail. We identify critical knowledge gaps in individual reports and highlight the underlying mechanisms and synergy between the different degradation routes. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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Other

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15 pages, 3495 KiB

Open AccessFeature PaperPerspective

High Entropy Alloys: Ready to Set Sail?

by Indranil Basu and Jeff Th. M. De Hosson

Metals 2020, 10(2), 194; https://doi.org/10.3390/met10020194 - 29 Jan 2020

Cited by 15 | Viewed by 5254

Abstract

Over the past decade, high entropy alloys (HEAs) have transcended the frontiers of material development in terms of their unprecedented structural and functional properties compared to their counterpart conventional alloys. The possibility to explore a vast compositional space further renders this area of research extremely promising in the near future for discovering society-changing materials. The introduction of HEAs has also brought forth a paradigm shift in the existing knowledge about material design and development. It is in this regard that a fundamental understanding of the metal physics of these alloys is critical in propelling mechanism-based HEA design. The current paper highlights some of the critical viewpoints that need greater attention in the future with respect to designing mechanically and functionally advanced materials. In particular, the interplay of large compositional gradients and defect topologies in these alloys and their corresponding impact on overall mechanical response are highlighted. From the point of view of functional response, such chemistry vis-à-vis topology correlations are extended to novel class of nano-porous HEAs that beat thermal coarsening effects despite a high surface to volume ratio owing to retarded diffusion kinetics. Recommendations on material design with regards to their potential use in diverse applications such as energy storage, actuators, and as piezoelectrics are additionally considered. Full article

(This article belongs to the Special Issue Complex Concentrated Alloys (CCAs) - Current Understanding and Future Opportunities)

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