Research

19 pages, 5419 KiB

Open AccessArticle

Thermodynamic and Ab Initio Design of Multicomponent Alloys Based on (Fe₅₀Mn₃₀Co₁₀Cr₁₀)-xBx (x = 0, 5, 7, 10, and 15 at.%)

by Rodrigo Vargas-Osorio, Laura Gabriela Torres-Mejia, Lais Mujica-Roncery, Jose Y. Aguilar-Hurtado and Katherine Paredes-Gil

Materials 2023, 16(16), 5579; https://doi.org/10.3390/ma16165579 - 11 Aug 2023

Cited by 1 | Viewed by 1074

Abstract

Multicomponent alloys have attained general interest in recent years due to their remarkable performance. Non-equiatomic alloys with boron addition as an interstitial element are being studied, exhibiting outstanding mechanical properties. In order to estimate the mechanical behavior of potential alloys, thermodynamic and ab [...] Read more.

Multicomponent alloys have attained general interest in recent years due to their remarkable performance. Non-equiatomic alloys with boron addition as an interstitial element are being studied, exhibiting outstanding mechanical properties. In order to estimate the mechanical behavior of potential alloys, thermodynamic and ab initio calculations were utilized in this work to investigate phase stability and stacking fault energy (SFE) for (Fe₅₀Mn₃₀Co₁₀Cr₁₀)-xBx (x = 0, 5, 7, 10, and 15 at.%) systems. Thermodynamic experiments revealed two structural variations of borides, M₂B(C16) with a tetragonal structure and M₂B(CB) with an orthorhombic structure. Borides precipitate when boron content increases, and the FCC matrix becomes deficient in Mn and Cr. According to ab initio calculations, the presence of boron in the FCC and HCP structures primarily disrupts the surroundings of the Fe and Mn atoms, resulting in an increased distortion of the crystal lattice. This is related to the antiferromagnetic condition of the alloys. Furthermore, for alloys with a low boron concentration, the stacking fault energy was found to be near 20 mJ/m² and greater than 50 mJ/m² when 10 and 15 at.% boron was added. As boron concentrations increase, M₂B borides are formed, generating changes in the matrix composition prone to fault-induced phase transitions that could modify and potentially impair mechanical properties. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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19 pages, 6871 KiB

Open AccessArticle

Study of the Mechanisms of Radiation Softening and Swelling upon Irradiation of TiTaNbV Alloys with He²⁺ Ions with an Energy of 40 keV

by Sholpan G. Giniyatova, Kayrat K. Kadyrzhanov, Dmitriy I. Shlimas, Daryn B. Borgekov, Vladimir V. Uglov, Artem L. Kozlovskiy and Maxim V. Zdorovets

Materials 2023, 16(11), 4031; https://doi.org/10.3390/ma16114031 - 28 May 2023

Cited by 1 | Viewed by 1227

Abstract

This paper presents simulation results of the ionization losses of incident He²⁺ ions with an energy of 40 keV during the passage of incident ions in the near-surface layer of alloys based on TiTaNbV with a variation of alloy components. For comparison, [...] Read more.

This paper presents simulation results of the ionization losses of incident He²⁺ ions with an energy of 40 keV during the passage of incident ions in the near-surface layer of alloys based on TiTaNbV with a variation of alloy components. For comparison, data on the ionization losses of incident He²⁺ ions in pure niobium, followed by the addition of vanadium, tantalum, and titanium to the alloy in equal stoichiometric proportions, are presented. With the use of indentation methods, the dependences of the change in the strength properties of the near-surface layer of alloys were determined. It was established that the addition of Ti to the composition of the alloy leads to an increase in resistance to crack resistance under high-dose irradiation, as well as a decrease in the degree of swelling of the near-surface layer. During tests on the thermal stability of irradiated samples, it was found that swelling and degradation of the near-surface layer of pure niobium affects the rate of oxidation and subsequent degradation, while for high-entropy alloys, an increase in the number of alloy components leads to an increase in resistance to destruction. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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21 pages, 8081 KiB

Open AccessArticle

Evaluation of Equiatomic CrMnFeCoNiCu System and Subsequent Derivation of a Non-Equiatomic MnFeCoNiCu Alloy

by Artashes Ter-Isahakyan and Thomas John Balk

Materials 2023, 16(6), 2455; https://doi.org/10.3390/ma16062455 - 19 Mar 2023

Viewed by 1068

Abstract

Investigation into non-equiatomic high-entropy alloys has grown in recent years due to questions about the role of entropy stabilization in forming single-phase solid solutions. Non-equiatomic alloys have been shown to retain the outstanding mechanical properties exhibited by their equiatomic counterparts and even improve [...] Read more.

Investigation into non-equiatomic high-entropy alloys has grown in recent years due to questions about the role of entropy stabilization in forming single-phase solid solutions. Non-equiatomic alloys have been shown to retain the outstanding mechanical properties exhibited by their equiatomic counterparts and even improve electrical, thermal, and magnetic properties, albeit with relaxed composition bounds. However, much remains to understand the processing–structure–property relationships in all classes of so-called high-entropy alloys (HEAs). Here, we are motivated by the natural phenomena of crystal growth and equilibrium conditions to introduce a method of HEA development where controlled processing conditions determine the most probable and stable composition. This is demonstrated by cooling an equiatomic CrMnFeCoNiCu alloy from the melt steadily over 3 days (cooling rate ~4 °C/h). The result is an alloy containing large Cr-rich precipitates and an almost Cr-free matrix exhibiting compositions within the MnFeCoNiCu system (with trace amounts of Cr). From this juncture, it is argued that the most stable composition is within the CrMnFeCoNiCu system rather than the CrMnFeCoNi system. With further optimization and evaluation, a unique non-equiatomic alloy, Mn₁₇Fe₂₁Co₂₄Ni₂₄Cu₁₄, is derived. The alloy solidifies and recrystallizes into a single-phase face-centered cubic (FCC) polycrystal. In addition to possible applications where Invar is currently utilized, this alloy can be used in fundamental studies that contrast its behavior with its equiatomic counterpart and shed light on the development of HEAs. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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14 pages, 2328 KiB

Open AccessArticle

Structure and Physical Properties of Mg_93−xZn_xCa₇ Metallic Glasses

by Štefan Michalik, Zuzana Molčanová, Michaela Šulíková, Katarína Kušnírová, Pál Jóvári, Jacques Darpentigny and Karel Saksl

Materials 2023, 16(6), 2313; https://doi.org/10.3390/ma16062313 - 14 Mar 2023

Viewed by 1180

Abstract

The Mg-Zn-Ca system has previously been proposed as the most suitable biodegradable candidate for biomedical applications. In this work, a series of ribbon specimens was fabricated using a melt-spinning technique to explore the glass-forming ability of the Mg-Zn-Ca system along the concentration line [...] Read more.

The Mg-Zn-Ca system has previously been proposed as the most suitable biodegradable candidate for biomedical applications. In this work, a series of ribbon specimens was fabricated using a melt-spinning technique to explore the glass-forming ability of the Mg-Zn-Ca system along the concentration line of 7 at.% of calcium. A glassy state is confirmed for Mg₅₀Zn₄₃Ca₇, Mg₆₀Zn₃₃Ca₇, and Mg₇₀Zn₂₃Ca₇. Those samples were characterised by standard methods to determine their mass density, hardness, elastic modulus, and crystallisation temperatures during devitrification. Their amorphous structure is described by means of pair distribution functions obtained by high-energy X-ray and neutron diffraction (HEXRD and ND) measurements performed at large-scale facilities. The contributions of pairs Mg-Mg, Mg-Zn, and Zn-Zn were identified. In addition, a transformation process from an amorphous to crystalline structure is followed in situ by HEXRD for Mg₆₀Zn₃₃Ca₇ and Mg₅₀Zn₄₃Ca₇. Intermetallic compounds IM1 and IM3 and hcp-Mg phase are proposed to be formed in multiple crystallisation eventss. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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12 pages, 1354 KiB

Open AccessArticle

(Magneto)Transport Properties of (TiZrNbNi)_1−xCu_x and (TiZrNbCu)_1−xCo_x Complex Amorphous Alloys

by Marko Kuveždić, Emil Tafra, Ignacio A. Figueroa and Mario Basletić

Materials 2023, 16(4), 1711; https://doi.org/10.3390/ma16041711 - 18 Feb 2023

Cited by 1 | Viewed by 997

Abstract

We present a systematic study of electrical resistivity, superconductive transitions and the Hall effect for three systems of compositionally complex amorphous alloys of early (TE) and late (TL) transition metals:

{(TiZrNbNi)}_{1 - x} {Cu}_{x}

and [...] Read more.

We present a systematic study of electrical resistivity, superconductive transitions and the Hall effect for three systems of compositionally complex amorphous alloys of early (TE) and late (TL) transition metals:

{(TiZrNbNi)}_{1 - x} {Cu}_{x}

and

{(TiZrNbCu)}_{1 - x} {Co}_{x}

in a broad composition range of

0 < x < 0.5

as well as

{Ti}_{0.30} {Zr}_{0.15} {Nb}_{0.15} {Cu}_{0.2} {Ni}_{0.2}

,

{Ti}_{0.15} {Zr}_{0.30} {Nb}_{0.15} {Cu}_{0.2} {Ni}_{0.2}

and

{Ti}_{0.15} {Zr}_{0.15} {Nb}_{0.30} {Cu}_{0.2} {Ni}_{0.2}

. All samples showed high resistivity at room temperature, 140–240

μ

Ω cm, and the superconducting transition temperatures decreased with increasing late transition metal content, similar to binary amorphous and crystalline high-entropy TE-TL alloys. The Hall coefficient

R_{H}

was temperature-independent and positive for all samples (except for (TiZrNbCu)

_{0.57}

Co

_{0.43}

), in good agreement with binary TE-TL alloys. Finally, for the temperature dependence of resistivity, as far as the authors are aware, we present a new model with two conduction channels, one of them being variable range hopping, such as the parallel conduction mode in the temperature range 20–200 K, with the exponent

p = 1 / 2

. We examine this in the context of variable range hopping in granular metals. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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16 pages, 3228 KiB

Open AccessArticle

Compositionally Complex Alloys: Some Insights from Photoemission Spectroscopy

by Petar Pervan, Vesna Mikšić Trontl, Ignacio Alejandro Figueroa, Tonica Valla, Ivo Pletikosić and Emil Babić

Materials 2023, 16(4), 1486; https://doi.org/10.3390/ma16041486 - 10 Feb 2023

Viewed by 1359

Abstract

Photoemission spectroscopy (PES) is an underrepresented part of current and past studies of compositionally complex alloys (CCA) such as high-entropy alloys (HEA) and their derivatives. PES studies are very important for understanding the electronic structure of materials, and are therefore essential in some [...] Read more.

Photoemission spectroscopy (PES) is an underrepresented part of current and past studies of compositionally complex alloys (CCA) such as high-entropy alloys (HEA) and their derivatives. PES studies are very important for understanding the electronic structure of materials, and are therefore essential in some cases for a correct description of the intrinsic properties of CCAs. Here, we present several examples showing the importance of PES. First, we show how the difference between the split-band structure and the common-band structure of the valence band (VB), observed by PES, can explain a range of properties of CCAs and alloys in general. A simple description of the band crossing in CCAs composed from the early and late transition metals showing a split band is discussed. We also demonstrate how a high-accuracy PES study can determine the variation in the density of states at the Fermi level as a function of Cu content in Ti-Zr-Nb-Ni-Cu metallic glasses. Finally, the first results of an attempt to single out the contributions of particular constituents in Cantor-type alloys to their VBs are presented. The basic principles of PES, the techniques employed in studies presented, and some issues associated with PES measurements are also described. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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14 pages, 8127 KiB

Open AccessArticle

Strange Metallicity and Magnetic Order in the CoNi(Cr/V) Medium-Entropy Alloy System

by Faisal Mustafa, Mehmet Egilmez, Wael Abuzaid, Sami El-Khatib, Tahir Nawaz, Shahbaz Ahmad and Serhat Alagoz

Materials 2023, 16(3), 1044; https://doi.org/10.3390/ma16031044 - 24 Jan 2023

Cited by 9 | Viewed by 1251

Abstract

CoNiCr is a prototypical example of topical multi-principle element alloys with superior cryogenic and high-temperature mechanical strength, corrosion, oxidation resistance, and yet-to-be-explored magnetic and electronic functionalities. The remarkable properties of this transition metal ternary system are not only due to atomic radii, electronic [...] Read more.

CoNiCr is a prototypical example of topical multi-principle element alloys with superior cryogenic and high-temperature mechanical strength, corrosion, oxidation resistance, and yet-to-be-explored magnetic and electronic functionalities. The remarkable properties of this transition metal ternary system are not only due to atomic radii, electronic configurational mismatch, and atomic volume misfit but are also dependent on the debated magnetically driven chemical short-range order. The current study focuses on the electric and magnetic properties of the single-phase face-centered cubic CoNi(Cr/V) system in which V is introduced to the system at the expense of Cr to fine-tune the volume misfit in the system. All the samples exhibited ultra-small magnetic moments due to the complex magnetic interactions of the constituent elements. The electric transport measurements revealed a strange metallicity evidenced through the observation of the linear temperature dependence of the resistivity. Our findings support the recent theoretical studies on the magnetically driven chemical short-range order of the CoNiCr system. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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12 pages, 3098 KiB

Open AccessArticle

Effect of Si and B on the Electrochemical Behavior of FeCoNiCr-Based High-Entropy Amorphous Alloys

by S. Leila Panahi, Pere Bruna and Eloi Pineda

Materials 2022, 15(24), 8897; https://doi.org/10.3390/ma15248897 - 13 Dec 2022

Cited by 3 | Viewed by 1257

Abstract

The ability to produce high-entropy alloys with an amorphous structure, so-called high-entropy metallic glasses (HEMGs), offers the possibility to produce new compositions with good mechanical properties and resistance to corrosion. In this study, corrosion behavior was studied in two HEMGs, FeCoNiCrB and FeCoNiCr(BSi). [...] Read more.

The ability to produce high-entropy alloys with an amorphous structure, so-called high-entropy metallic glasses (HEMGs), offers the possibility to produce new compositions with good mechanical properties and resistance to corrosion. In this study, corrosion behavior was studied in two HEMGs, FeCoNiCrB and FeCoNiCr(BSi). In both cases, the total amount of metalloid atoms was kept constant at 20 at.%. The electrochemical behavior of these alloys was studied by means of linear polarization resistance (LPR) measurements and electrochemical impedance spectroscopy in a 3 wt.% NaCl solution. The effect of corrosion was characterized by using X-ray photoelectron spectroscopy (XPS) and the surface morphology was checked using a scanning electron microscope (SEM). The results show that samples with B but without Si exhibit better corrosion resistance due to its chemical homogeneity and lack of structural heterogeneity. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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17 pages, 8748 KiB

Open AccessArticle

Structure, Properties, and Corrosion Behavior of Ti-Rich TiZrNbTa Medium-Entropy Alloys with β+α″+α′ for Biomedical Application

by Ka-Kin Wong, Hsueh-Chuan Hsu, Shih-Ching Wu, Tun-Li Hung and Wen-Fu Ho

Materials 2022, 15(22), 7953; https://doi.org/10.3390/ma15227953 - 10 Nov 2022

Cited by 5 | Viewed by 1322

Abstract

Five Ti-rich β+α″+α′ Ti–Zr–Nb–Ta biomedical medium-entropy alloys with excellent mechanical properties and corrosion resistance were developed by considering thermodynamic parameters and using the valence electron concentration formula. The results of this study demonstrated that the traditional valence electron concentration formula for predicting phases [...] Read more.

Five Ti-rich β+α″+α′ Ti–Zr–Nb–Ta biomedical medium-entropy alloys with excellent mechanical properties and corrosion resistance were developed by considering thermodynamic parameters and using the valence electron concentration formula. The results of this study demonstrated that the traditional valence electron concentration formula for predicting phases is not entirely applicable to medium-entropy alloys. All solution-treated samples with homogeneous compositions were obtained at a low temperature (900 °C) and within a short period (20 min). All solution-treated samples exhibited low elastic moduli ranging from 49 to 57 GPa, which were significantly lower than those of high-entropy alloys with β phase. Solution-treated Ti₆₅–Zr₂₉–Nb₃–Ta₃ exhibited an ultra-high bending strength (1102 MPa), an elastic recovery angle (>30°), and an ultra-low elastic modulus (49 GPa), which are attributed to its α″ volume fraction as high as more than 60%. The pitting potentials of all samples were higher than 1.8 V, and their corrosion current densities were lower than 10^–5 A/cm³ in artificially simulated body fluid at 37 °C. The surface oxide layers on Ti₆₅–Zr₂₉–Nb₃–Ta₃ comprised TiO₂, ZrO₂, Nb₂O₅, and Ta₂O₅ (as discovered through X-ray photoelectron spectroscopy) and provided the alloy with excellent corrosion and pitting resistance. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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8 pages, 2370 KiB

Open AccessArticle

Different Types of Particle Effects in Creep Tests of CoCrFeNiMn High-Entropy Alloy

by Ferdinand Dobeš, Hynek Hadraba, Zdeněk Chlup and Jiří Matějíček

Materials 2022, 15(20), 7363; https://doi.org/10.3390/ma15207363 - 20 Oct 2022

Viewed by 1161

Abstract

Compressive creep tests were performed on a CoCrFeNiMn equiatomic alloy with the dispersion of (i) aluminum nitride or (ii) boron nitride at temperatures of 973 K and 1073 K. The results are compared with previously published creep rates of the unreinforced matrix alloy [...] Read more.

Compressive creep tests were performed on a CoCrFeNiMn equiatomic alloy with the dispersion of (i) aluminum nitride or (ii) boron nitride at temperatures of 973 K and 1073 K. The results are compared with previously published creep rates of the unreinforced matrix alloy and the alloy when strengthened by yttrium + titanium oxides. The comparison reveals that the creep rate is essentially unchanged by the presence of aluminum nitride particles, whereas it is reduced by the presence of oxide particles. Boron nitride particles do not influence the creep rate at low stresses but reduce it substantially at high stresses. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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43 pages, 94001 KiB

Open AccessArticle

The Effect of Fe Addition in the RM(Nb)IC Alloy Nb–30Ti–10Si–2Al–5Cr–3Fe–5Sn–2Hf (at.%) on Its Microstructure, Complex Concentrated and High Entropy Phases, Pest Oxidation, Strength and Contamination with Oxygen, and a Comparison with Other RM(Nb)ICs, Refractory Complex Concentrated Alloys (RCCAs) and Refractory High Entropy Alloys (RHEAs)

by Nikos Vellios and Panos Tsakiropoulos

Materials 2022, 15(17), 5815; https://doi.org/10.3390/ma15175815 - 23 Aug 2022

Cited by 4 | Viewed by 1273

Abstract

In this work, the RM(Nb)IC alloy Nb–30Ti–10Si–5Cr–5Sn–3Fe–2Al–2Hf (NV2) was studied in the as-cast and heat-treated conditions; its isothermal oxidation at 700, 800 and 900 °C and its room temperature hardness and specific strength were compared with other Sn-containing RM(Nb)ICs—in particular, the alloy Nb–24Ti–18Si–5Cr–5Fe–5Sn [...] Read more.

In this work, the RM(Nb)IC alloy Nb–30Ti–10Si–5Cr–5Sn–3Fe–2Al–2Hf (NV2) was studied in the as-cast and heat-treated conditions; its isothermal oxidation at 700, 800 and 900 °C and its room temperature hardness and specific strength were compared with other Sn-containing RM(Nb)ICs—in particular, the alloy Nb–24Ti–18Si–5Cr–5Fe–5Sn (NV5)—and with RCCAs and RHEAs. The addition of Fe (a) stabilised Nb_ss; A15–Nb₃X (X = Al, Si and Sn) and Nb₃Si; metastable Nb₃Si-m’ and Nb₅Si₃ silicides; (b) supported the formation of eutectic Nb_ss + Nb₅Si₃; (c) suppressed pest oxidation at all three temperatures and (d) stabilised a Cr- and Fe-rich phase instead of a C14–Nb(Cr,Fe)₂ Laves phase. Complex concentrated (or compositionally complex) and/or high entropy phases co-existed with “conventional” phases in all conditions and after oxidation at 800 °C. In NV2, the macrosegregation of Si decreased but liquation occurred at T >1200 °C. A solid solution free of Si and rich in Cr and Ti was stable after the heat treatments. The relationships between solutes in the various phases, between solutes and alloy parameters and between alloy hardness or specific strength and the alloy parameters were established (parameters δ, Δχ and VEC). The oxidation of NV2 at 700 °C was better than the other Sn-containing RM(Nb)ICs with/without Fe addition, even better than RM(Nb)IC alloys with lower vol.% Nb_ss. At 800 °C, the mass change of NV2 was slightly higher than that of NV5, and at 900 °C, both alloys showed scale spallation. At 800 °C, both alloys formed a more or less continuous layer of A15–Nb₃X below the oxide scale, but in NV5, this compound was Sn-rich and severely oxidised. At 800 °C, in the diffusion zone (DZ) and the bulk of NV2, Nb_ss was more severely contaminated with oxygen than Nb₅Si₃, and the contamination of A15–Nb₃X was in-between these phases. The contamination of all three phases was more severe in the DZ. The contamination of all three phases in the bulk of NV5 was more severe compared with NV2. The specific strength of NV2 was comparable with that of RCCAs and RHEAs, and its oxidation at all three temperatures was significantly better than RHEAs and RCCAs. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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17 pages, 5751 KiB

Open AccessArticle

Vacancy Energetics and Diffusivities in the Equiatomic Multielement Nb-Mo-Ta-W Alloy

by Xinran Zhou, Sicong He and Jaime Marian

Materials 2022, 15(15), 5468; https://doi.org/10.3390/ma15155468 - 08 Aug 2022

Cited by 10 | Viewed by 1902

Abstract

In this work, we study vacancy energetics in the equiatomic Nb-Mo-Ta-W alloy, especially vacancy formation and migration energies, using molecular statics calculations based on a spectral neighbor analysis potential specifically developed for Nb-Mo-Ta-W. We consider vacancy properties in bulk environments as well as [...] Read more.

In this work, we study vacancy energetics in the equiatomic Nb-Mo-Ta-W alloy, especially vacancy formation and migration energies, using molecular statics calculations based on a spectral neighbor analysis potential specifically developed for Nb-Mo-Ta-W. We consider vacancy properties in bulk environments as well as near edge dislocation cores, including the effect of short-range order (SRO) by preparing supercells through Metropolis Monte-Carlo relaxations and temperature on the calculation. The nudged elastic band (NEB) method is applied to study vacancy migration energies. Our results show that both vacancy formation energies and vacancy migration energies are statistically distributed with a wide spread, on the order of 1.0 eV in some cases, and display a noticeable dependence on SRO. We find that, in some cases, vacancies can form with very low energies at edge dislocation cores, from which we hypothesize the formation of stable ‘superjogs’ on edge dislocation lines. Moreover, the large spread in vacancy formation energies results in an asymmetric thermal sampling of the formation energy distribution towards lower values. This gives rise to effective vacancy formation energies that are noticeably lower than the distribution averages. We study the effect that this phenomenon has on the vacancy diffusivity in the alloy and discuss the implications of our findings on the structural features of Nb-Mo-Ta-W. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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18 pages, 11862 KiB

Open AccessArticle

Characterisation of a Novel Complex Concentrated Alloy for Marine Applications

by Ioana-Cristina Badea, Ioana Csaki, Beatrice-Adriana Serban, Nicolae Constantin, Dumitru Mitrica, Marian Burada, Ioana Anasiei, Mihai Tudor Olaru, Andreea-Nicoleta Ghita and Ana-Maria Julieta Popescu

Materials 2022, 15(9), 3345; https://doi.org/10.3390/ma15093345 - 06 May 2022

Viewed by 1269

Abstract

Complex concentrated alloys (CCAs) are a new family of materials with near equimolar compositions that fluctuate depending on the characteristics and destination of the material. CCAs expand the compositional limits of the traditional alloys, displaying new pathways in material design. A novel light [...] Read more.

Complex concentrated alloys (CCAs) are a new family of materials with near equimolar compositions that fluctuate depending on the characteristics and destination of the material. CCAs expand the compositional limits of the traditional alloys, displaying new pathways in material design. A novel light density Al₅Cu_0.5Si_0.2Zn_1.5Mg_0.2 alloy was studied to determine the structural particularities and related properties. The alloy was prepared in an induction furnace and then annealed under a protective atmosphere. The resulted specimens were analysed by chemical, structural, mechanical, and corrosion resistance. The structural analyses revealed a predominant FCC and BCC solid solution structure. The alloy produced a compression strength of 500–600 MPa, comparable with conventional aluminium alloys. The corrosion resistance in 3.5% NaCl solution was 0.3424 mm/year for as-cast and 0.1972 mm/year for heat-treated alloy, superior to steel, making the alloy a good candidate for marine applications. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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8 pages, 3778 KiB

Open AccessArticle

Reducing the Core Losses of Fe-Si-B Amorphous Alloy Ribbons by High Cooling Rate Planar Flow Casting

by Deren Li, Wenjun Wang, Tiancheng Liu, Lijun Li and Zhichao Lu

Materials 2022, 15(3), 894; https://doi.org/10.3390/ma15030894 - 25 Jan 2022

Cited by 2 | Viewed by 2209

Abstract

In the planar flow casting (PFC) process, the cooling rate significantly affects the structure and properties of a cast ribbon. The influence of the thermal conductivity of the cooling wheel substrate on cooling rate was simulated by a numerical method, and it is [...] Read more.

In the planar flow casting (PFC) process, the cooling rate significantly affects the structure and properties of a cast ribbon. The influence of the thermal conductivity of the cooling wheel substrate on cooling rate was simulated by a numerical method, and it is shown that a higher thermal conductivity of the cooling wheel substrate leads to a higher cooling rate in the PFC process. Two copper-beryllium (Cu-2Be) rings with thermal conductivities of 175.3 W/m·K and 206.5 W/m·K were manufactured and installed onto a wheel core as the substrate of the cooling wheel. The effects of cooling rate on the soft magnetic properties of Fe-Si-B amorphous ribbons were investigated by pragmatic ribbon casting. The results show that the increment in the thermal conductivity of the cooling wheel substrate from 175.3 W/m·K to 206.5 W/m·K lowered the coercive force of amorphous ribbon from 2.48 A/m to 1.92 A/m and reduced the core losses at 1.4 T and 50 Hz by up to 22.1%. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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38 pages, 6183 KiB

Open AccessArticle

Transition from High-Entropy to Conventional Alloys: Which Are Better?

by Emil Babić, Đuro Drobac, Ignacio Alejandro Figueroa, Mathilde Laurent-Brocq, Željko Marohnić, Vesna Mikšić Trontl, Damir Pajić, Loїc Perrière, Petar Pervan, Gyorgy Remenyi, Ramir Ristić, Amra Salčinović Fetić, Damir Starešinić and Krešo Zadro

Materials 2021, 14(19), 5824; https://doi.org/10.3390/ma14195824 - 05 Oct 2021

Cited by 6 | Viewed by 2852

Abstract

The study of the transition from high-entropy alloys (HEAs) to conventional alloys (CAs) composed of the same alloying components is apparently important, both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of the corresponding [...] Read more.

The study of the transition from high-entropy alloys (HEAs) to conventional alloys (CAs) composed of the same alloying components is apparently important, both for understanding the formation of HEAs and for proper evaluation of their potential with respect to that of the corresponding CAs. However, this transition has thus far been studied in only two types of alloy systems: crystalline alloys of iron group metals (such as the Cantor alloy and its derivatives) and both amorphous (a-) and crystalline alloys, TE-TL, of early (TE = Ti, Zr, Nb, Hf) and late (TL = Co, Ni, Cu) transition metals. Here, we briefly overview the main results for the transition from HEAs to CAs in these alloy systems and then present new results for the electronic structure (ES), studied with photoemission spectroscopy and specific heat, atomic structure, thermal, magnetic and mechanical properties of a-TE-TL and Cantor-type alloys. A change in the properties of the alloys studied on crossing from the HEA to the CA concentration range mirrors that in the ES. The compositions of the alloys having the best properties depend on the alloy system and the property selected. This emphasizes the importance of knowing the ES for the design of new compositional complex alloys with the desired properties. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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17 pages, 5911 KiB

Open AccessArticle

Microstructure, Hardness, and Elastic Modulus of a Multibeam-Sputtered Nanocrystalline Co-Cr-Fe-Ni Compositional Complex Alloy Film

by Péter Nagy, Nadia Rohbeck, Zoltán Hegedűs, Johann Michler, László Pethö, János L. Lábár and Jenő Gubicza

Materials 2021, 14(12), 3357; https://doi.org/10.3390/ma14123357 - 17 Jun 2021

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Abstract

A nanocrystalline Co-Cr-Ni-Fe compositional complex alloy (CCA) film with a thickness of about 1 micron was produced by a multiple-beam-sputtering physical vapor deposition (PVD) technique. The main advantage of this novel method is that it does not require alloy targets, but rather uses [...] Read more.

A nanocrystalline Co-Cr-Ni-Fe compositional complex alloy (CCA) film with a thickness of about 1 micron was produced by a multiple-beam-sputtering physical vapor deposition (PVD) technique. The main advantage of this novel method is that it does not require alloy targets, but rather uses commercially pure metal sources. Another benefit of the application of this technique is that it produces compositional gradient samples on a disk surface with a wide range of elemental concentrations, enabling combinatorial analysis of CCA films. In this study, the variation of the phase composition, the microstructure (crystallite size and defect density), and the mechanical performance (hardness and elastic modulus) as a function of the chemical composition was studied in a combinatorial Co-Cr-Ni-Fe thin film sample that was produced on a surface of a disk with a diameter of about 10 cm. The spatial variation of the crystallite size and the density of lattice defects (e.g., dislocations and twin faults) were investigated by X-ray diffraction line profile analysis performed on the patterns taken by synchrotron radiation. The hardness and the elastic modulus were measured by the nanoindentation technique. It was found that a single-phase face-centered cubic (fcc) structure was formed for a wide range of chemical compositions. The microstructure was nanocrystalline with a crystallite size of 10–27 nm and contained a high lattice defect density. The hardness and the elastic modulus values measured for very different compositions were in the ranges of 8.4–11.8 and 182–239 GPa, respectively. Full article

(This article belongs to the Special Issue Compositional Complex Alloys: From Amorphous to High-Entropy)

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