High-entropy alloys fabricated via powder metallurgy. A critical review

High-entropy alloys (HEAs) have attracted a great deal of interest over the last 14 years. One reason for this level of interest is related to these alloys breaking the alloying principles that have been applied for many centuries. Thus, HEAs usually possess a single phase (contrary to expectations according to the composition of the alloy) and exhibit a high level of performance in different properties related to many developing areas in industry. Despite this significant interest, most HEAs have been developed via ingot metallurgy. More recently, powder metallurgy (PM) has appeared as an interesting alternative for further developing this family of alloys to possibly widen the field of nanostructures in HEAs and improve some capabilities of these alloys. In this paper, PM methods applied to HEAs are reviewed, and some possible ways to develop the use of powders as raw materials are introduced

The effect of zr addition on melting temperature, microstructure, recrystallization and mechanical properties of a cantor high entropy alloy

The effect of Zr addition on the melting temperature of the CoCrFeMnNi High Entropy Alloy (HEA), known as the “Cantor’s Alloy”, is investigated, together with its micro-structure, mechanical properties and thermomechanical recrystallization process. The base and Zr-modified alloys are obtained by vacuum induction melting of mechanically pre-alloyed powders. Raw materials are then cold rolled and annealed. recrystallization occurred during the heat treatment of the cold-rolled HEA. The alloys are characterized by X-ray diffraction, electron microscopy, thermal analyses, mechanical spectroscopy and indentation measures. The main advantages of Zr addition are: (1) a fast vacuum induction melting process; (2) the lower melting temperature, due to Zr eutectics formation with all the Cantor’s alloy elements; (3) the good chemical alloy homogeneity; and (4) the mechanical properties improvement of re-crystallized grains with a coherent structure. The crystallographic lattice of both alloys results in FCC. The Zr-modified HEA presents a higher recrystallization temperature and smaller grain size after recrystallization with respect to the Cantor’s alloy, with precipitation of a coherent second phase, which enhances the alloy hardness and strength

Laser powder bed fusion of Fe60(CoCrNiMn)40 medium-entropy alloy with excellent strength-ductility balance

In this study, Fe60(CoCrNiMn)40 medium-entropy alloy (MEA) was fabricated by laser powder bed fusion (LPBF) via mixing of pure Fe and FeCoCrNiMn powders, the processability, microstructure and mechanical properties were systematically investigated, and the mechanism of strengthening and toughening were revealed through combination of experiments and molecular dynamics (MD) simulations. Results show that fraction of BCC phase decreased gradually with increasing volume energy density (VED), and thus heterostructue with varying FCC and BCC phases were produced through regulating the VED. The Fe60(CoCrNiMn)40 MEA (with scanning speeds of 700 and 800 mm/s) showed excellent strength-plasticity balance (e.g. 476 MPa, 612 MPa and 63 %) compared to the equiatomic FeCoCrNiMn HEA, which is ascribed to the synergistic strengthening and toughening effects involving the twinning induced plasticity (TWIP) and the reinforcement caused by the BCC phase (act as reinforced particle) embedded in the FCC matrix

High-Entropy Coatings (HEC) for High-Temperature Applications: Materials, Processing, and Properties

High-entropy materials (HEM), including alloys, ceramics, and composites, are a novel class of materials that have gained enormous attention over the past two decades. These multi-component novel materials with unique structures always have exceptionally good mechanical properties and phase stability at all temperatures. Of particular interest for high-temperature applications, e.g., in the aerospace and nuclear sectors, is the new concept of high-entropy coatings (HEC) on low-cost metallic substrates, which has just emerged during the last few years. This exciting new virgin field awaits exploration by materials scientists and surface engineers who are often equipped with high-performance computational modelling tools, high-throughput coating deposition technologies and advanced materials testing/characterisation methods, all of which have greatly shortened the development cycle of a new coating from years to months/days. This review article reflects on research progress in the development and application of HEC focusing on high-temperature applications in the context of materials/composition type, coating process selection and desired functional properties. The importance of alloying addition is highlighted, resulting in suppressing oxidation as well as improving corrosion and diffusion resistance in a variety of coating types deposited via common deposition processes. This review provides an overview of this hot topic, highlighting the research challenges, identifying gaps, and suggesting future research activity for high temperature applications

High Entropy Alloys for Energy Conversion and Storage: A Review of Grain Boundary Wetting Phenomena

This research was funded by the Russian Ministry of Science and Higher Education (contract no. 075-15-2021-945 grant no. 13.2251.21.0013). Support from the University of the Basque Country (project GIU19/019) and from the Basque Government (project IT1714-22) is also acknowledged.The multicomponent alloys with nearly equal concentration of components, also known as high entropy alloys (HEAs), were first proposed 22 years ago. The HEAs quickly became very important in materials science due to their unique properties. Nowadays, the HEAs are frequently used in energy conversion and storage applications. HEAs can consist of five, six or more components. Plasma cladding permits coating of the large surfaces of cheap substrates with (often expensive) HEAs and to enlarge, in such a way, their application area. The large-area coatings deposited by plasma cladding possess multiple advantages such as low thermal distortion, very high energy density, as well as low dilution of the substrate material. Plasma cladding ensures good metallurgical bonding between coating and substrate. The costs of operation and equipment are also very attractive. During plasma cladding, the mixed powders are blown by carrier gas into a plasma torch or are positioned on a substrate. This powder mixture is then melted in or under the plasma torch. The plasma torch, in turn, sequentially scans the substrate. After finalizing the crystallization process, the solid polycrystal appears which contains few residual melts. This remaining melt can completely or incompletely wet the grain boundaries (GBs) in solid phase of the polycrystal. These completely or incompletely wetted GBs can strongly influence the microstructure of HEA coatings and their morphology. In this review we analyze the GB wetting HEAs containing one phase in HEAs with two, three and more phases, as well as in HEAs reinforced with particles of carbides, nitrides, borides, or oxides. We also analyze the microstructure of the rather thick coatings after plasma cladding after additional laser remelting and observe how GB wetting changes over their thickness.--//-- Published under the CC BY 4.0 licence.Russian Ministry of Science and Higher Education (contract no. 075-15-2021-945 grant no. 13.2251.21.0013); University of the Basque Country (project GIU19/019); Basque Government (project IT1714-22); Institute of Solid State Physics, University of Latvia as the Center of Excellence acknowledges funding from the European Union’s Horizon 2020 Framework Programme H2020- WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART2

Superfunctional high-entropy alloys and ceramics by severe plastic deformation

High-entropy alloys and ceramics containing at least five principal elements have received high attention in recent years for various mechanical and functional applications. The application of severe plastic deformation (SPD), particularly the high-pressure torsion (HPT) method combined with the CALPHAD and first-principles calculations, resulted in the development of numerous superfunctional high-entropy materials with superior properties compared to the normal functions of engineering materials. This article reviews the recent advances in the application of SPD to achieving superfunctional high-entropy materials. These superfunctional properties include (i) ultrahigh hardness levels in high-entropy alloys which are comparable to ceramics, (ii) high yield strength and good hydrogen embrittlement resistance in high-entropy alloys; (iii) high strength, low elastic modulus, and high biocompatibility in high-entropy alloys, (iv) fast and reversible hydrogen storage in high-entropy alloys and corresponding hydrides, (v) photovoltaic performance and photocurrent generation on high-entropy semiconductors, (vi) photocatalytic oxygen and hydrogen production on high-entropy oxides and oxynitrides from water splitting, and (vii) CO2 photoreduction on high-entropy ceramics. These findings introduce SPD as not only a processing tool to improve the properties of existing high-entropy materials but also as a synthesis tool to synthesize novel high-entropy materials with superior properties compared with conventional engineering materials

Microstructure and mechanical properties of oxide dispersion strengthened high-entropy alloys CoCrFeMnNi and CrFe₂MnNi

High-entropy alloys (HEAs) CoCrFeMnNi and CrFe₂MnNi, dispersion-strengthened by pre-synthesized nanooxides composition of 80%Y₂O₃+20%ZrO₂ (mol.%) were obtained by mechanical alloying followed by compaction and sintering. Average grain size of the oxide dispersion-strengthened (ODS) alloys was about 2 μm. Oxide precipitates in alloys are characterized by the presence of small particles with an average size of about 10 nm and a density of ≈ 10²¹ m⁻³, as well as small amount of larger particles sizes of 50…150 nm. The qualitative composition of particles of different sizes has been established. Mechanical properties of HEAs were studied at different temperatures. It is shown that strengthening of the studied alloys by nanooxide particles leads to a significant increase in strength characteristics.Методом механічного легування з наступним компактуванням та спіканням отримано високоентропійні сплави CoCrFeMnNi та CrFe₂MnNi, що зміцнені попередньо синтезованими нанооксидами складу 80%Y₂O₃+20%ZrO₂ (mol.%). Середній розмір зерен у дисперсно-зміцнених сплавах близько 2 мкм. Оксидні виділення в сплавах характеризуються присутністю дрібних часток з середнім розміром близько 10 нм і щільністю ≈ 10²¹ м⁻³, а також незначної кількості більших часток з розмірами 50…150 нм. Встановлено якісний склад часток різного розміру. Досліджені механічні властивості сплавів при різних температурах. Показано, що міцнісні характеристики суттєво підвищуються при зміцненні сплавів нанооксидними частками.Методом механического легирования с последующим компактированием и спеканием получены высокоэнтропийные сплавы CoCrFeMnNi и CrFe₂MnNi, дисперсно-упрочненные предварительно синтезированными нанооксидами состава 80%Y₂O₃+20%ZrO₂ (mol.%). Средний размер зерен в дисперсно-упрочненных сплавах составил примерно 2 мкм. Оксидные выделения в сплавах характеризуются наличием мелких частиц со средним размером около 10 нм и плотностью ≈ 10²¹ м⁻³, а также незначительного количества больших частиц с размерами 50…150 нм. Установлен качественный состав частиц разного размера. Исследованы механические свойства сплавов при разных температурах. Показано, что прочностные характеристики значительно повышаются при упрочнении сплавов нанооксидными частицами

High Entropy Materials: Challenges and Prospects

This book is a reprint of a special issue of Metals (ISSN 2075-4701), titled High Entropy Materials: Challenges and Prospects. It is a compilation of nine articles from different aspects of high-entropy materials. The book primarily focuses on high-entropy alloys, the first emergent high-entropy materials, but also covers high-entropy ceramics and high-entropy composites, which are the extensions of high-entropy alloys. The articles on high-entropy alloys cover some important facets in the field such as phase structures, mechanical properties, laser beam welding, design of soft magnetic alloys, and potential as biomaterials. In addition, there are one article introducing the potential of using high-entropy carbides as hard metals for machining, and one another on high-entropy composite studying the microstructures and tribological properties of the FeCoNiCuAl-TiC composite. The goal of this reprinted book is essentially two-fold. In the first place, it offers a platform for researchers in the broad field of high-entropy materials to communicate their views and recent research on the subject. Next, it reports challenges in the sub-fields of high-entropy materials and inspires researchers to continue to practice diligence to resolve these challenges and advance high-entropy materials solidly. We hope that readers in the field feel encouraged, inspired, and challenged by the book, and readers outside the field can grasp some basic ideals of high-entropy materials and their potential to the society as a family of novel materials

Complex Concentrated Alloys (CCAs)

This book is a collection of several unique articles on the current state of research on complex concentrated alloys, as well as their compelling future opportunities in wide ranging applications. Complex concentrated alloys consist of multiple principal elements and represent a new paradigm in structural alloy design. They show a range of exceptional properties that are unachievable in conventional alloys, including high strength–ductility combination, resistance to oxidation, corrosion/wear resistance, and excellent high-temperature properties. The research articles, reviews, and perspectives are intended to provide a wholistic view of this multidisciplinary subject of interest to scientists and engineers

Effect of heat treatments on the microstructure and hardness of high-entropy alloy

V tejto práci je študovaná neekviatomická Al0.2Co1.5CrFeNi1.5Ti vysoko entropická zliatina, ktorá bola vyrobená pomocou vákuového indukčného tavenia. Zliatina v odliatom stave bola analyzovaná a tepelne spracovaná pri teplote 1000 °C po dobu 5h, a následne podrobená tepelnému spracovaniu pri teplote 750 °C po dobu ďalších 5h, s cieľom skúmania vplyvu teploty a doby tepelného spracovania na fázové zloženie, mikroštruktúru a mechanické vlastnosti. Na vyhodnotenie možných fáz prítomných v zliatine bol použitý pseudobinárny fázový diagram (CALPHAD). Mikroštruktúra zliatin bola charakterizovaná a chemicky analyzovaná pomocou röntgenovej difrakcie (XRD), elektrónovej mikroskopie (SEM) a energeticky disperznej spektroskopie. Výsledné vyhodnotenie tvrdosti materiálu prebehlo pomocou skúšok mikrotvrdosti a nanoindentácie.In this work, a non-equiatomic Al0.2Co1.5CrFeNi1.5Ti high-entropy alloy was produced through the vacuum induction melting process. The as-cast alloy was analyzed, then heat treated at 1000 °C for 5h, and subsequent heat treatment at 750 °C for an additional 5h took place, in order to investigate the effect of heat treatment temperature and time on the phase composition, microstructure, and mechanical properties of the alloy in all states. A pseudo binary phase diagram (CALPHAD) was performed to evaluate the possible phases present in the alloy. The alloy‘s microstructures were characterized and analyzed chemically by X-ray diffraction (XRD), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). Microhardness and nanoindentation testing was performed to evaluate the hardness of the material.