Research

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14 pages, 4205 KiB

Open AccessArticle

Mechanical and Corrosion Behavior of Zr-Doped High-Entropy Alloy from CoCrFeMoNi System

by Santiago Brito-Garcia, Julia Mirza-Rosca, Victor Geanta and Ionelia Voiculescu

Materials 2023, 16(5), 1832; https://0-doi-org.brum.beds.ac.uk/10.3390/ma16051832 - 23 Feb 2023

Cited by 5 | Viewed by 1368

The aim of the paper is to study the Zr addition effect on the mechanical properties and corrosion behavior of a high-entropy alloy from the CoCrFeMoNi system. This alloy was designed to be used for components in the geothermal industry that are exposed [...] Read more.

The aim of the paper is to study the Zr addition effect on the mechanical properties and corrosion behavior of a high-entropy alloy from the CoCrFeMoNi system. This alloy was designed to be used for components in the geothermal industry that are exposed to high temperature and corrosion. Two alloys, one Zr-free (named Sample 1) and another one doped with 0.71 wt.% Zr (named Sample 2), were obtained in a vacuum arc remelting equipment from high-purity granular raw materials. Microstructural characterization and quantitative analysis by SEM and EDS were performed. The Young modulus values for the experimental alloys were calculated on the basis of a three-point bending test. Corrosion behavior was estimated by linear polarization test and by electrochemical impedance spectroscopy. The addition of Zr resulted in a decrease in the value of the Young modulus but also in a decrease in corrosion resistance. The beneficial effect of Zr on the microstructure was the grain refinement, and this ensured a good deoxidation of the alloy. Full article

(This article belongs to the Special Issue Multi-Functional High Entropy Alloys: From Design to Application)

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9 pages, 5134 KiB

Open AccessArticle

Investigations on the Phase Transformations, Equilibria and Athermal ω in Ni-Ga-Cr Ternary System

by Jingjing Ruan, Yuyuan Chen, Kosei Kobayashi, Nobufumi Ueshima and Katsunari Oikawa

Materials 2022, 15(21), 7617; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15217617 - 30 Oct 2022

Viewed by 1165

Abstract

In the present work, the phase equilibria of the Ni-Ga-Cr ternary system at 850, 1000 and 1150 °C were experimentally investigated to provide the essential data for developing the high-entropy shape memory alloys (HESMAs) containing Ni, Ga and Cr. At 850 °C, in [...] Read more.

In the present work, the phase equilibria of the Ni-Ga-Cr ternary system at 850, 1000 and 1150 °C were experimentally investigated to provide the essential data for developing the high-entropy shape memory alloys (HESMAs) containing Ni, Ga and Cr. At 850 °C, in the Ni-rich portion, the B2 phase shows equilibrium with the L12 phase when the Cr content is less than 10.49 at. %, while displaying the equilibrium with L12 and BCC phases when the Cr content increases. The B2 + L12 + BCC changes into B2 + FCC + BCC three-phase equilibria from 850 to 1150 °C, as the L12 phase region becomes narrow with rising temperature. The two-phase equilibrium, B2 + BCC, was found at all the isothermal sections investigated. Other three-phase equilibria were also discovered: B2 + α-Cr3Ga + BCC and Ni2Ga3 + α-Cr3Ga + L at 850 °C, and B2 + α-Cr3Ga + L at 1000 °C. Significantly, an athermal ω intermetallic compound with the space group of P

\bar{3}

m1 was observed distributing at the B2 phase in the quenched Ni45.98-Ga25.50-Cr28.52, Ni42.23-Ga15.70-Cr42.07 and Ni16.54-Ga13.63-Cr69.83 (at. %) alloys after being annealed at 1150 °C for 10 days. The high-resolution transmission electron microscopy (HRTEM) results reveal that the ω shows a crystallographic orientation of

[1 \bar{1} 0]_{B 2} / / [11 \bar{2} 0]_{ω}

;

{(111)}_{B 2} / / {(0001)}_{ω}

with the B2 parent phase. Full article

(This article belongs to the Special Issue Multi-Functional High Entropy Alloys: From Design to Application)

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15 pages, 6383 KiB

Open AccessArticle

Non-Aqueous Electrodeposition and Characterization of AlCrCuFeNi High Entropy Alloy Thin Films

by Beatrice-Adriana Serban, Mihai-Tudor Olaru, Ioana-Cristina Badea, Dumitru Mitrica, Marian Burada, Ioana Anasiei, Mihai Ghita, Albert-Ioan Tudor, Cristian-Alexandru Matei, Ana Maria Julieta Popescu, Virgil Constantin, Florina Branzoi, Cristian Dobrescu and Nicolae Constantin

Materials 2022, 15(17), 6007; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15176007 - 31 Aug 2022

Cited by 4 | Viewed by 1832

Abstract

Materials used in the marine industry are exposed to extreme conditions, so it is necessary to meet remarkable characteristics, such as mechanical resistance, low density, and good corrosion resistance. The challenging environment requires continuous performance improvements, so this work is focused on developing [...] Read more.

Materials used in the marine industry are exposed to extreme conditions, so it is necessary to meet remarkable characteristics, such as mechanical resistance, low density, and good corrosion resistance. The challenging environment requires continuous performance improvements, so this work is focused on developing new materials with superior properties, using the electrochemical deposition technique, which are convenient for marine engineering. High-entropy alloys have been attracting tremendous interest in many applications, due to their simple crystal structures and advantageous physical-chemical properties, such as high strength, anti-corrosion, erosion, and electro-magnetic capabilities. To identify the most appropriate compositions, MatCalc software was used to predict the structure and characteristics of the required materials, and thermodynamic and kinetic criteria calculations were performed. The modelling processes generated a series of optimal compositions in the AlCrCuFeNi alloy system, that are suitable to be used in anticorrosive and tribological applications. The composition and morphology of the obtained high entropy alloy thin films revealed a uniform structure, with a small grain profile. The corrosion resistance was investigated in artificial seawater to observe the behavior of the newly developed materials in demanding conditions, and the results showed improved results compared to the copper foil substrate. Full article

(This article belongs to the Special Issue Multi-Functional High Entropy Alloys: From Design to Application)

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11 pages, 24481 KiB

Open AccessArticle

Microstructural Evolution and Mechanical Properties of Non-Equiatomic (CoNi)_74.66Cr₁₇Fe₈C_0.34 High-Entropy Alloy

by You Sub Kim, Hobyung Chae, E-Wen Huang, Jayant Jain, Stefanus Harjo, Takuro Kawasaki, Sun Ig Hong and Soo Yeol Lee

Materials 2022, 15(4), 1312; https://0-doi-org.brum.beds.ac.uk/10.3390/ma15041312 - 10 Feb 2022

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Abstract

In this study, we manufactured a non-equiatomic (CoNi)_74.66Cr₁₇Fe₈C_0.34 high-entropy alloy (HEA) consisting of a single-phase face-centered-cubic structure. We applied in situ neutron diffraction coupled with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) to investigate [...] Read more.

In this study, we manufactured a non-equiatomic (CoNi)_74.66Cr₁₇Fe₈C_0.34 high-entropy alloy (HEA) consisting of a single-phase face-centered-cubic structure. We applied in situ neutron diffraction coupled with electron backscattered diffraction (EBSD) and transmission electron microscopy (TEM) to investigate its tensile properties, microstructural evolution, lattice strains and texture development, and the stacking fault energy. The non-equiatomic (CoNi)_74.66Cr₁₇Fe₈C_0.34 HEA revealed a good combination of strength and ductility in mechanical properties compared to the equiatomic CoNiCrFe HEA, due to both stable solid solution and precipitation-strengthened effects. The non-equiatomic stoichiometry resulted in not only a lower electronegativity mismatch, indicating a more stable state of solid solution, but also a higher stacking fault energy (SFE, ~50 mJ/m²) due to the higher amount of Ni and the lower amount of Cr. This higher SFE led to a more active motion of dislocations relative to mechanical twinning, resulting in severe lattice distortion near the grain boundaries and dislocation entanglement near the twin boundaries. The abrupt increase in the strain hardening rate (SHR) at the 1~3% strain during tensile deformation might be attributed to the unusual stress triaxiality in the {200} grain family. The current findings provide new perspectives for designing non-equiatomic HEAs. Full article

(This article belongs to the Special Issue Multi-Functional High Entropy Alloys: From Design to Application)

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9 pages, 40748 KiB

Open AccessArticle

Effect of Grain Size on Carburization Characteristics of the High-Entropy Equiatomic CoCrFeMnNi Alloy

by Hyunbin Nam, Jeongwon Kim, Namkyu Kim, Sangwoo Song, Youngsang Na, Jun-Ho Kim and Namhyun Kang

Materials 2021, 14(23), 7199; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14237199 - 25 Nov 2021

Cited by 5 | Viewed by 1733

Abstract

In this study, the carburization characteristics of cast and cold-rolled CoCrFeMnNi high-entropy alloys (HEAs) with various grain sizes were investigated. All specimens were prepared by vacuum carburization at 940 °C for 8 h. The carburized/diffused layer was mainly composed of face-centered cubic structures [...] Read more.

In this study, the carburization characteristics of cast and cold-rolled CoCrFeMnNi high-entropy alloys (HEAs) with various grain sizes were investigated. All specimens were prepared by vacuum carburization at 940 °C for 8 h. The carburized/diffused layer was mainly composed of face-centered cubic structures and Cr₇C₃ carbide precipitates. The carburized/diffused layer of the cold-rolled specimen with a fine grain size (~1 μm) was thicker (~400 μm) than that of the carburized cast specimen (~200 μm) with a coarse grain size (~1.1 mm). In all specimens, the carbides were formed primarily through grain boundaries, and their distribution varied with the grain sizes of the specimens. However, the carbide precipitates of the cast specimen were formed primarily at the grain boundaries and were unequally distributed in the specific grains. Owing to the non-uniform formation of carbides in the carburized cast specimen, the areas in the diffused layer exhibited various carbide densities and hardness distributions. Therefore, to improve the carburization efficiency of equiatomic CoCrFeMnNi HEAs, it is necessary to refine the grain sizes. Full article

(This article belongs to the Special Issue Multi-Functional High Entropy Alloys: From Design to Application)

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7 pages, 3751 KiB

Open AccessArticle

In-Situ TEM Annealing Observation of Helium Bubble Evolution in Pre-Irradiated FeCoNiCrTi_0.2 Alloys

by Huanhuan He, Zhiwei Lin, Shengming Jiang, Xiaotian Hu, Jian Zhang and Zijing Huang

Materials 2021, 14(13), 3727; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14133727 - 02 Jul 2021

Cited by 1 | Viewed by 2097

Abstract

The FeCoNiCrTi_0.2 high-entropy alloys fabricated by vacuum arc melting method, and the annealed pristine material, are face centered cubic structures with coherent γ’ precipitation. Samples were irradiated with 50 keV He⁺ ions to a fluence of 2 × 10¹⁶ ions/cm [...] Read more.

The FeCoNiCrTi_0.2 high-entropy alloys fabricated by vacuum arc melting method, and the annealed pristine material, are face centered cubic structures with coherent γ’ precipitation. Samples were irradiated with 50 keV He⁺ ions to a fluence of 2 × 10¹⁶ ions/cm² at 723 K, and an in situ annealing experiment was carried out to monitor the evolution of helium bubbles during heating to 823 and 923 K. The pristine structure of FeCoNiCrTi_0.2 samples and the evolution of helium bubbles during in situ annealing were both characterized by transmission electron microscopy. The annealing temperature and annealing time affect the process of helium bubbles evolution and formation. Meanwhile, the grain boundaries act as sinks to accumulate helium bubbles. However, the precipitation phase seems have few effects on the helium bubble evolution, which may be due to the coherent interface and same structure of γ’ precipitation and matrix. Full article

(This article belongs to the Special Issue Multi-Functional High Entropy Alloys: From Design to Application)

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16 pages, 6177 KiB

Open AccessArticle

Effects of the Replacement of Co with Ni on the Microstructure, Mechanical Properties, and Age Hardening of AlCo_1−xCrFeNi_1+x High-Entropy Alloys

by Che-Fu Lee and Tao-Tsung Shun

Materials 2021, 14(10), 2665; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14102665 - 19 May 2021

Cited by 5 | Viewed by 1687

Abstract

In this study, effects of the replacement of Co with Ni on the microstructure, mechanical properties, and age hardening of high-entropy alloys of AlCo_1−xCrFeNi_1+x (x = molar ratio; x = 0, 0.5, 1, denoted as X₀, X_0.5 [...] Read more.

In this study, effects of the replacement of Co with Ni on the microstructure, mechanical properties, and age hardening of high-entropy alloys of AlCo_1−xCrFeNi_1+x (x = molar ratio; x = 0, 0.5, 1, denoted as X₀, X_0.5, and X₁, respectively) were investigated. These three alloys exhibited a dendritic structure comprising an ordered BCC matrix, a BCC phase, and an FCC or an ordered FCC phase. From X₀ to X₁ alloys, the yield stress and compressive stress decreased from 1202 and 1790 MPa to 693 and 1537 MPa, respectively. However, fracture strain increased from 0.15 to 0.42. Peak age hardening at 600 °C for the X₀ alloy was due to the precipitation of the (Cr,Fe)-rich σ phase. Peak age hardening for the X_0.5 and X₁ alloys was observed at 500 °C because of the precipitation of the σ phase and BCC phase, respectively. Full article

(This article belongs to the Special Issue Multi-Functional High Entropy Alloys: From Design to Application)

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Review

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35 pages, 1839 KiB

Open AccessReview

Synthesis Route, Microstructural Evolution, and Mechanical Property Relationship of High-Entropy Alloys (HEAs): A Review

by Omoyemi Temitope Onawale, Prince Valentine Cobbinah, Rivel Armil Nzeukou and Wallace Rwisayi Matizamhuka

Materials 2021, 14(11), 3065; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14113065 - 04 Jun 2021

Cited by 18 | Viewed by 4627

Abstract

Microstructural phase evolution during melting and casting depends on the rate of cooling, the collective mobility of constituent elements, and binary constituent pairs. Parameters used in mechanical alloying and spark plasma sintering, the initial structure of binary alloy pairs, are some of the [...] Read more.

Microstructural phase evolution during melting and casting depends on the rate of cooling, the collective mobility of constituent elements, and binary constituent pairs. Parameters used in mechanical alloying and spark plasma sintering, the initial structure of binary alloy pairs, are some of the factors that influence phase evolution in powder-metallurgy-produced HEAs. Factors such as powder flowability, laser power, powder thickness and shape, scan spacing, and volumetric energy density (VED) all play important roles in determining the resulting microstructure in additive manufacturing technology. Large lattice distortion could hinder dislocation motion in HEAs, and this could influence the microstructure, especially at high temperatures, leading to improved mechanical properties in some HEAs. Mechanical properties of some HEAs can be influenced through solid solution hardening, precipitation hardening, grain boundary strengthening, and dislocation hardening. Despite the HEA system showing reliable potential engineering properties if commercialized, there is a need to examine the effects that processing routes have on the microstructure in relation to mechanical properties. This review discusses these effects as well as other factors involved. Full article

(This article belongs to the Special Issue Multi-Functional High Entropy Alloys: From Design to Application)

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