Research

Open AccessArticle

Optimization of Sputtering Process for Medium Entropy Alloy Nanotwinned CoCrFeNi Thin Films by Taguchi Method

by

Jing-Yi Zhong

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Jian-Jie Wang

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Fan-Yi Ouyang

Materials 2022, 15(22), 8238; https://doi.org/10.3390/ma15228238 - 20 Nov 2022

Viewed by 481

Abstract

We demonstrate a systematic study optimizing the properties of CoCrFeNi medium entropy alloy (MEA) thin films by tuning the deposition parameters of the pulsed direct current (DC) magnetron sputtering process. The chemical composition and microstructure of thin films were studied with energy dispersive [...] Read more.

We demonstrate a systematic study optimizing the properties of CoCrFeNi medium entropy alloy (MEA) thin films by tuning the deposition parameters of the pulsed direct current (DC) magnetron sputtering process. The chemical composition and microstructure of thin films were studied with energy dispersive X-ray spectroscopy (EDS), an X-ray diffractometer (XRD) and a transmission electron microscope (TEM). Abundant nanotwins and the dual face-centered cubic−hexagonal close-packed (FCC-HCP) phases were formed in some specimens. The Taguchi experimental method and analysis of variance (ANOVA) were applied to find the optimized parameters. The control factors are five deposition parameters: substrate bias, substrate temperature, working pressure, rotation speed and pulsed frequency. According to the signal-to-noise ratio results, the optimized parameters for low electrical resistivity (98.2 ± 0.8 μΩ·cm), low surface roughness (0.5 ± 0.1 nm) and high hardness (9.3 ± 0.2 GPa) were achieved and verified with confirmed experiments. Full article

(This article belongs to the Special Issue Future Trends in High-Entropy Alloys)

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Open AccessArticle

Irradiation Damage Independent Deuterium Retention in WMoTaNbV

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Materials 2022, 15(20), 7296; https://doi.org/10.3390/ma15207296 - 19 Oct 2022

Cited by 1 | Viewed by 729

Abstract

High entropy alloys are a promising new class of metal alloys with outstanding radiation resistance and thermal stability. The interaction with hydrogen might, however, have desired (H storage) or undesired effects, such as hydrogen-induced embrittlement or tritium retention in the fusion reactor wall. [...] Read more.

High entropy alloys are a promising new class of metal alloys with outstanding radiation resistance and thermal stability. The interaction with hydrogen might, however, have desired (H storage) or undesired effects, such as hydrogen-induced embrittlement or tritium retention in the fusion reactor wall. High entropy alloy WMoTaNbV and bulk W samples were used to study the quantity of irradiation-induced trapping sites and properties of D retention by employing thermal desorption spectrometry, secondary ion mass spectrometry, and elastic recoil detection analysis. The D implantation was not found to create additional hydrogen traps in WMoTaNbV as it does in W, while 90 at% of implanted D is retained in WMoTaNbV, in contrast to 35 at% in W. Implantation created damage predicted by SRIM is 0.24 dpa in WMoTaNbV, calculated with a density of

6.044 \times 10^{22}

atoms/cm

^{3}

. The depth of the maximum damage was 90 nm. An effective trapping energy for D in WMoTaNbV was found to be about 1.7 eV, and the D emission temperature was close to 700 °C. Full article

(This article belongs to the Special Issue Future Trends in High-Entropy Alloys)

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Open AccessArticle

Effect of Varying Plasma Powers on High-Temperature Applications of Plasma-Sprayed Al_0.5CoCrFeNi₂Ti_0.5 Coatings

by

Sammy Kiplangat Rotich

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Ngetich Gilbert Kipkirui

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Tzu-Tang Lin

and

Shih-Hsun Chen

Materials 2022, 15(20), 7198; https://doi.org/10.3390/ma15207198 - 15 Oct 2022

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Abstract

In this work, the microstructure and mechanical properties of atmospheric plasma-sprayed coatings of Al_0.5CoCrFeNi₂Ti_0.5, prepared using gas-atomized powders at varying spray powers, are studied in as-sprayed and heat-treated conditions. Gas-atomized powders had spherical shapes and uniform element distributions, [...] Read more.

In this work, the microstructure and mechanical properties of atmospheric plasma-sprayed coatings of Al_0.5CoCrFeNi₂Ti_0.5, prepared using gas-atomized powders at varying spray powers, are studied in as-sprayed and heat-treated conditions. Gas-atomized powders had spherical shapes and uniform element distributions, with major FCC phases and metastable BCC phases. The metastable BCC phase transformed to ordered and disordered BCC phases when sufficient energy was applied during the plasma-spraying process. During the heat treatment process for 2 hrs, disordered BCCs transformed into ordered BCCs, while the intensity of the FCC peaks increased. Spraying power plays a significant role in the microstructure and mechanical properties of plasma sprayed because at a high power, coatings exhibit better mechanical properties due to their dense microstructures resulting in less defects. As the plasma current was increased from 500 A to 700 A, the coatings’ hardness increased by approximately 21%, which is directly proportional to the decreased wear rate of the coatings at high spraying powers. As the coatings experienced heat treatments, the coatings sprayed with a higher spraying power showed higher hardness and wear resistances. Precipitation strengthening played a significant role in the hardness and wear resistances of the coatings due to the addition of the titanium element. Full article

(This article belongs to the Special Issue Future Trends in High-Entropy Alloys)

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Open AccessArticle

Dynamic Polarization Behaviors of Equimolar CoCrFeNi High-Entropy Alloy Compared with 304 Stainless Steel in 0.5 M H₂SO₄ Aerated Aqueous Solution

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Materials 2022, 15(19), 6976; https://doi.org/10.3390/ma15196976 - 08 Oct 2022

Viewed by 573

Abstract

Three corrosion potentials and three corrosion current densities are clearly identified before the passivation for both dynamic polarization curves of equimolar CoCrFeNi high-entropy alloy (HEA) and 304 stainless steel (304SS) in 0.5 M H₂SO₄ aerated aqueous solution, by decomposing anodic [...] Read more.

Three corrosion potentials and three corrosion current densities are clearly identified before the passivation for both dynamic polarization curves of equimolar CoCrFeNi high-entropy alloy (HEA) and 304 stainless steel (304SS) in 0.5 M H₂SO₄ aerated aqueous solution, by decomposing anodic and cathodic polarization curves. The passivated current density of the former is greater than the latter, compliant with not only the constant of solubility product (k_sp) and redox equilibrium potential (E_eq) of each metal hydroxide but also the sequence of bond energy (E_b) for monolayer hydroxide on their facets derived from the first principle founded on density function theory. However, the total amount of ion releasing from HEA is less than 304SS, since the hydroxide/oxide film formed in the air of the latter containing greater amounts of Fe(Ⅱ) and Mn(Ⅱ) is less stable around corrosion potentials while they are further oxidized into more stable Fe(Ⅲ) and Mn(ⅢorⅣ) with much lower k_sp, leading to the much less increasing ratios of ion releases from 0.25 to 0.6 V. Full article

(This article belongs to the Special Issue Future Trends in High-Entropy Alloys)

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Open AccessArticle

Microstructure and Mechanical Properties of Intergranular Boride Precipitation-Toughened HfMoNbTaTiZr Refractory High-Entropy Alloy

by

Ping-Hsu Ko

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Ya-Jing Lee

and

Shou-Yi Chang

Materials 2022, 15(19), 6666; https://doi.org/10.3390/ma15196666 - 26 Sep 2022

Viewed by 572

Abstract

To develop strong refractory high-entropy alloys for use at elevated temperatures as well as to overcome grain-boundary brittleness, an equimolar HfMoNbTaTiZr alloy was prepared, and a minor amount of boron (0.1 at.%) was added into the alloy. The microstructures of the alloys were [...] Read more.

To develop strong refractory high-entropy alloys for use at elevated temperatures as well as to overcome grain-boundary brittleness, an equimolar HfMoNbTaTiZr alloy was prepared, and a minor amount of boron (0.1 at.%) was added into the alloy. The microstructures of the alloys were characterized, and their macro-to-microscale mechanical properties were measured. The microstructural observations indicated that the matrices of both the alloys were composed of a body-centered cubic solid-solution structure, and the added boron induced the precipitation of hexagonal close-packed borides (most likely the (Hf, Zr)B₂) at the grain boundaries. The modulus and hardness of differently oriented grains were about equivalent, suggesting a diminished anisotropy, and many small slips occurred on multiple {110} planes. While the hardness of the matrix was not increased, the intergranular precipitation of the borides markedly raised the hardness of the grain boundaries. Owing to the enhanced grain boundary cohesion, the work hardenability and ductility were effectively improved with the addition of boron. Full article

(This article belongs to the Special Issue Future Trends in High-Entropy Alloys)

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Open AccessArticle

The Observation of Cellular Precipitation in an Ni₃₆Co₁₈Cr₂₀Fe₁₉Al₇ High-Entropy Alloy after Quenching and Annealing

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Gurumayum Robert Kenedy

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Korir Rosemary Chemeli

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Wei-Chun Cheng

Materials 2022, 15(19), 6613; https://doi.org/10.3390/ma15196613 - 23 Sep 2022

Cited by 1 | Viewed by 602

Abstract

High-entropy alloys (HEAs) comprise a minimum of five major elements. These alloys show some special characteristics, such as excellent mechanical and high temperature properties. The development of the HEAs requires a knowledge of phase transformations during alloy making procedures. The phase transformations of [...] Read more.

High-entropy alloys (HEAs) comprise a minimum of five major elements. These alloys show some special characteristics, such as excellent mechanical and high temperature properties. The development of the HEAs requires a knowledge of phase transformations during alloy making procedures. The phase transformations of an Ni₃₆Co₁₈Cr₂₀Fe₁₉Al₇ HEA were studied in this research. The alloy underwent hot forging, cold rolling, annealing at and quenching from 1323 K, and isothermal holding at 873 K. The alloy is a single face-centered cubic (FCC) phase in the as-quenched condition. After annealing at 873 K, not only fine coherent L1₂ particles precipitated homogeneously in the FCC matrix, but lamellae of FCC and L1₂ phases also developed from the grain boundaries. Both lamellar FCC and L1₂ grains have a cubic-on-cubic orientation relationship (OR). The composition of the lamellar L1₂ phase is Ni₆₀Co₈Cr₆Fe₆Al₂₀, and that of the lamellar FCC phase is Ni₃₁Co₁₅Cr₂₈Fe₂₁Al₄. Cellular precipitation occurs in the HEA, and the high-temperature FCC (γ) transforms to a lamella of low-temperature FCC (γ₁), and an L1₂ phase, i.e., γ → γ₁+L1₂. Full article

(This article belongs to the Special Issue Future Trends in High-Entropy Alloys)

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Open AccessCommunication

Remarkable Enhanced Mechanical Properties of TiAlCrNbV Medium-Entropy Alloy with Zr Additions

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Jason Shian-Ching Jang

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Materials 2022, 15(18), 6324; https://doi.org/10.3390/ma15186324 - 12 Sep 2022

Viewed by 670

Abstract

Most medium entropy alloys (MEAs) exhibit excellent mechanical properties, but their applications are limited because of their high density. This study explores a series of lightweight nonequiatomic Ti₆₅(AlCrNbV)_35-xZr_x (x = 3, 5, 7, and 10) MEAs with a [...] Read more.

Most medium entropy alloys (MEAs) exhibit excellent mechanical properties, but their applications are limited because of their high density. This study explores a series of lightweight nonequiatomic Ti₆₅(AlCrNbV)_35-xZr_x (x = 3, 5, 7, and 10) MEAs with a low density, high strength, and high ductility. To achieve solid solution strengthening, Zr with a large atomic radius was used. In addition, various thermomechanical treatment parameters were adopted to further improve the MEAs’ mechanical properties. The density of the MEAs was revealed to be approximately 5 g/cm³, indicating that they were lightweight. Through an X-ray diffraction analysis, the MEAs were revealed to have a single body-centered cubic structure not only in the as-cast state but also after thermomechanical treatment. In terms of mechanical properties, all the as-cast MEAs with Zr additions achieved excellent performance (>1000 MPa tensile yield strength and 20% tensile ductility). In addition, hot rolling effectively eliminated the defects of the MEAs; under a given yield strength, hot-rolled MEAs exhibited superior ductility relative to non-hot-rolled MEAs. Overall, the Ti₆₅(AlCrNbV)₂₈Zr₇ MEAs exhibited an optimum combination of mechanical properties (yield strength > 1200 MPa, plastic strain > 15%) after undergoing hot rolling 50%, cold rolling 70%, and rapid annealing for 30 to 50 s (at a temperature of approximately 850 °C) with a heating rate of 15 K/s. With their extremely high specific yield strength (264 MPa·g/cm³) and high ductility (22%), the Ti₆₅(AlCrNbV)₂₈Zr₇ MEAs demonstrate considerable potential for energy and transportation applications. Full article

(This article belongs to the Special Issue Future Trends in High-Entropy Alloys)

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Open AccessArticle

Corrosion Behavior of CrFeCoNiV_x (x = 0.5 and 1) High-Entropy Alloys in 1M Sulfuric Acid and 1M Hydrochloric Acid Solutions

by

Chun-Huei Tsau

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Jo-Yi Chen

and

Tien-Yu Chien

Materials 2022, 15(10), 3639; https://doi.org/10.3390/ma15103639 - 19 May 2022

Viewed by 683

Abstract

CrFeCoNiV_x high-entropy alloys were prepared by arc-melting, and the microstructures and corrosion properties of these alloys were studied. The CrFeCoNiV_0.5 alloy had a granular structure; the matrix was a face-centered cubic (FCC) structure, and the second phase was a σ phase [...] Read more.

CrFeCoNiV_x high-entropy alloys were prepared by arc-melting, and the microstructures and corrosion properties of these alloys were studied. The CrFeCoNiV_0.5 alloy had a granular structure; the matrix was a face-centered cubic (FCC) structure, and the second phase was a σ phase with a tetragonal structure. The CrFeCoNiV alloy had a dendritic structure; the dendrites in this alloy showed an FCC phase, and the interdendrities had a eutectic structure of FCC and σ phases. Therefore, CrFeCoNiV was much harder than the CrFeCoNiV_0.5 alloy due to the dendritic structures. The potentiodynamic polarization test and electrochemical impedance spectroscopy were used to evaluate the corrosion behavior of the CrFeCoNiV_x high-entropy alloys in deaerated 1M sulfuric acid and 1M hydrochloric acid solutions. The results indicated that the CrFeCoNiV_0.5 alloy had a better corrosion resistance because of the granular structure. Full article

(This article belongs to the Special Issue Future Trends in High-Entropy Alloys)

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Open AccessArticle

The Effect of Increasing Nickel Content on the Microstructure, Hardness, and Corrosion Resistance of the CuFeTiZrNi_x High-Entropy Alloys

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Andromeda Dwi Laksono

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Yee-Wen Yen

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Alberto S. Pasana

Materials 2022, 15(9), 3098; https://doi.org/10.3390/ma15093098 - 25 Apr 2022

Viewed by 1013

Abstract

In recent years, high-entropy alloys (HEAs) that contain fine grains of intermetallic compounds (IMCs) have gained increasing attention as they have been shown to exhibit both high mechanical strength and strong corrosion resistance. One such class of HEAs is that of CuFeTiZrNi alloys. [...] Read more.

In recent years, high-entropy alloys (HEAs) that contain fine grains of intermetallic compounds (IMCs) have gained increasing attention as they have been shown to exhibit both high mechanical strength and strong corrosion resistance. One such class of HEAs is that of CuFeTiZrNi alloys. In this study, we have investigated the effect of increasing Ni content on the microstructure, hardness, and corrosion resistance of the CuFeTiZrNi_x alloys (where x = 0.1, 0.3, 0.5, 0.8, 1.0 in a molar ratio). The alloys used in this study were prepared in an arc melting furnace and then annealed at 900 °C. First-principles calculations of the bulk modulus were also performed for each alloy. The results revealed that increasing the Ni content had several effects. Firstly, the microstructure of the CuFeTiZrNi_x alloys changed from B2_BCC and Laves_C14 in the CuFeTiZrNi_0.1 and CuFeTiZrNi_0.3 alloys to FCC, B2_BCC, and Laves_C14 in the CuFeTiZrNi_0.5 alloys; and to FCC, B2_BCC, Cu₅₁Zr₁₄, and Laves_C14 in the CuFeTiZrNi_0.8 and CuFeTiZrNi_1.0 alloys. Secondly, IMCs arising from a combination of the refractory elements (Ti and Zr) and atomic size differences were found in the interdendritic region. Thirdly, as the Ni content in the CuFeTiZrNi_x alloys increased, the hardness decreased, but the corrosion resistance increased. Full article

(This article belongs to the Special Issue Future Trends in High-Entropy Alloys)

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