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Intermetallics: Synthesis, Structure, Function

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A special issue of Molecules (ISSN 1420-3049). This special issue belongs to the section "Materials Chemistry".

Deadline for manuscript submissions: closed (31 July 2020) | Viewed by 14739

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Dr. Pavel Novak

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Department of Metals and Corrosion Engineering, University of Chemistry and Technology, Technická 5, 166 28 Prague, Czech Republic
Interests: intermetallic alloys; powder metallurgy; titanium alloys; aluminum alloys; mechanical alloying; spark plasma sintering; high-entropy alloys
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Dear Colleagues,

Intermetallics are promising compounds with various functional properties, such as excellent corrosion resistance and high temperature mechanical properties, hydrogen storage ability, shape memory or superconductivity. Due to them, they already found many interesting applications, ranging from dental amalgams and nitinol stents in medicine to modern high-temperature alloys for new generation of jet engines for airplanes. I believe that the application range of them can be even wider, because many of their properties are still not described and some interesting compounds not discovered yet. Please help us to foster the science in this amazing field of science.

We kindly invite you to submit a manuscript(s) for this Special Issue. Full papers, communications, and reviews are all welcome.

Dr. Pavel Novak
Guest Editor

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Keywords

synthesis and processing of intermetallics
structure of intermetallics
functional intermetallic materials
high-temperature intermetallics
shape memory materials
hydrogen storage in intermetallics

Published Papers (6 papers)

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Research

11 pages, 4051 KiB

Open AccessArticle

The Effect of Simultaneous Si and Ti/Mo Alloying on High-Temperature Strength of Fe₃Al-Based Iron Aluminides

by Věra Vodičková, Martin Švec, Pavel Hanus, Pavel Novák, Antonín Záděra, Vojtěch Keller and Petra Pazourková Prokopčáková

Molecules 2020, 25(18), 4268; https://doi.org/10.3390/molecules25184268 - 17 Sep 2020

Cited by 9 | Viewed by 1904

Abstract

The effect of phase composition and morphology on high-temperature strength in the compression of Fe-Al-Si-based iron aluminides manufactured by casting was investigated. The structure and high-temperature strength in the compression of three alloys—Fe28Al5Si, Fe28Al5Si2Mo, and Fe28Al5Si2Ti—were studied. Long-term (at 800 °C for 100 h) annealing was performed for the achievement of structural stability. The phase composition and grain size of alloys were primarily described by means of scanning electron microscopy equipped with energy dispersive analysis and Electron Backscatter Diffraction (EBSD). The phase composition was verified by X-ray diffraction (XRD) analysis. The effect of Mo and Ti addition as well as the effect of long-term annealing on high-temperature yield stress in compression were investigated. Both additives—Mo and Ti—affected the yield stress values positively. Long-term annealing of Fe28Al5Si-X iron aluminide alloyed with Mo and Ti deteriorates yield stress values slightly due to grain coarsening. Full article

(This article belongs to the Special Issue Intermetallics: Synthesis, Structure, Function)

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17 pages, 8531 KiB

Open AccessArticle

Comparative Study of Microstructure and Mechanical Properties of Two TiAl-Based Alloys Reinforced with Carbide Particles

by Juraj Lapin, Kateryna Kamyshnykova and Alena Klimova

Molecules 2020, 25(15), 3423; https://doi.org/10.3390/molecules25153423 - 28 Jul 2020

Cited by 8 | Viewed by 2248

Abstract

Microstructure and mechanical properties of two TiAl-based alloys with nominal composition Ti-42.6Al-8.7Nb-0.3Ta-2.0C and Ti-41.0Al-8.7Nb-0.3Ta-3.6C (in at.%) were investigated and compared. The alloys were prepared by vacuum induction melting, followed by centrifugal casting. The as-cast samples were subjected to hot isostatic pressing and heat treatment consisting of solution annealing in β (Ti-based solid solution) phase field, cooling at a constant rate and stabilization annealing. The microstructure of the alloys consists of α₂ (Ti₃Al) + γ (TiAl) lamellar grains, single γ phase, coarse Ti₂AlC particles, and irregular shaped α₂ phase. The increase in the content of C at the expense of decreasing Al in the studied alloys affects solid-state phase transformation temperatures and leads to a decrease in size of grains and primary Ti₂AlC particles, increase in the volume fraction of reinforcing carbide particles, decrease in the volume fraction of lamellar colonies, and widening of the grain boundaries. Long-term ageing at 800 °C has no effect on the grain size but leads to the formation of Ti₄Al₃Nb particles and increase in interlamellar spacing. The Vickers hardness, microhardness of lamellar grains, indentation nanohardness, and elastic modulus of the boundary γ phase decrease during ageing. The Ti-42.6Al-8.7Nb-0.3Ta-2.0C alloy shows improved creep resistance compared to that of Ti-41.0Al-8.7Nb-0.3Ta-3.6C and some reference TiAl-based alloys at a temperature of 800 °C and applied stress of 200 MPa. Full article

(This article belongs to the Special Issue Intermetallics: Synthesis, Structure, Function)

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16 pages, 5707 KiB

Open AccessArticle

The Influence of Powder Milling on Properties of SPS Compacted FeAl

by Alena Michalcová, Murat Özkan, Pavol Mikula, Ivo Marek, Anna Knaislová, Jaromír Kopeček and Dalibor Vojtěch

Molecules 2020, 25(9), 2263; https://doi.org/10.3390/molecules25092263 - 11 May 2020

Cited by 8 | Viewed by 2352

Abstract

The Fe-28 at.% Al alloy was studied in this article. The aim was to describe the influence of gas atomized powder pre-milling before SPS (Spark Plasma Sintering) sintering on the structure and properties of the bulk materials. The initial powder was milled for 0.5, 1, and 8 h. It was proven that 1 h milling leads to the change in size and morphology of the particles, B2→A2 phase transformation, and to the contamination with the material from a milling vessel. Powder materials were compacted by the SPS process at 900, 1000, and 1100 °C. The differences between the bulk materials were tested by LM, SEM, and TEM microscopy, XRD, and neutron diffraction methods. It was proven that, although the structures of initial powder (B2) and milled powder (A2) were different, both provide after-sintering material with the same structure (D0₃) with similar structural parameters. Higher hardness and improved ductility of the material sintered from the milled powder are likely caused by the change in chemical composition during the milling process. Full article

(This article belongs to the Special Issue Intermetallics: Synthesis, Structure, Function)

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15 pages, 5098 KiB

Open AccessArticle

Metallurgical Preparation of Nb–Al and W–Al Intermetallic Compounds and Characterization of Their Microstructure and Phase Transformations by DTA Technique

by Tomas Cegan, Daniel Petlak, Katerina Skotnicova, Jan Jurica, Bedrich Smetana and Simona Zla

Molecules 2020, 25(8), 2001; https://doi.org/10.3390/molecules25082001 - 24 Apr 2020

Cited by 9 | Viewed by 2718

Abstract

The possibilities of metallurgical preparation of 40Nb-60Al and 15W-85Al intermetallic compounds (in at.%) by plasma arc melting (PAM) and vacuum induction melting (VIM) were studied. Both methods allow easy preparation of Nb–Al alloys; however, significant evaporation of Al was observed during the melting, which affected the resulting chemical composition. The preparation of W–Al alloys was more problematic because there was no complete re-melting of W during PAM and VIM. However, the combination of PAM and VIM allowed the preparation of W–Al alloy without any non-melted parts. The microstructure of Nb–Al alloys consisted of Nb₂Al and NbAl₃ intermetallic phases, and W–Al alloys consisted mainly of needle-like WAl₄ intermetallic phase and Al matrix. The effects of melting conditions on chemical composition, homogeneity, and microstructure were determined. Differential thermal analysis was used to determine melting and phase transformation temperatures of the prepared alloys. Full article

(This article belongs to the Special Issue Intermetallics: Synthesis, Structure, Function)

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13 pages, 6533 KiB

Open AccessArticle

Formation of Phases in Reactively Sintered TiAl₃ Alloy

by Andrea Školáková, Pavel Salvetr, Jindřich Leitner, Tomáš Lovaši and Pavel Novák

Molecules 2020, 25(8), 1912; https://doi.org/10.3390/molecules25081912 - 21 Apr 2020

Cited by 15 | Viewed by 2688

Abstract

This work highlights new results on the synthesis of the TiAl₃ intermetallic phase using self-propagating high-temperature synthesis. This method is considered a promising sintering route for intermetallic compounds. It was found that the reactions proceed in two stages. Below the melting point of aluminum, the Ti₂Al₅ phase forms at 450 °C after long annealing times by a direct solid-state reaction between the aluminum and titanium, and is converted consequently to TiAl₃. This is a completely new finding; until now, many authors have believed in the preferential formation of the TiAl₃ phase. The second stage, the self-propagating strongly exothermic reaction, proceeds above the melting point of aluminum. It leads to the formation of the TiAl₃ phase accompanied by Ti₂Al₅ and Ti₃Al phases. The reaction mechanism was shown in the form of chemical equations, which were supported by calculating Gibbs energy. Reaction temperatures (T_onset, T_maximum, and T_offset) were determined after induction heating thanks to recording by an optical pyrometer. This finding provides completely new opportunities for the determination of activation energy at heating rates, in which common calorimeters are not able to detect a response or even measure. Now, the whole procedure will become accessible. Full article

(This article belongs to the Special Issue Intermetallics: Synthesis, Structure, Function)

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11 pages, 4726 KiB

Open AccessArticle

Formation of Mo₅Si₃/Mo₃Si–MgAl₂O₄ Composites via Self-Propagating High-Temperature Synthesis

by Chun-Liang Yeh and Yin-Chien Chen

Molecules 2020, 25(1), 83; https://doi.org/10.3390/molecules25010083 - 24 Dec 2019

Cited by 10 | Viewed by 2210

Abstract

In situ formation of intermetallic/ceramic composites composed of molybdenum silicides (Mo₅Si₃ and Mo₃Si) and magnesium aluminate spinel (MgAl₂O₄) was conducted by combustion synthesis with reducing stages in the mode of self-propagating high-temperature synthesis (SHS). The SHS process combined intermetallic combustion between Mo and Si with metallothermic reduction of MoO₃ by Al in the presence of MgO. Experimental evidence showed that combustion velocity and temperature decreased with increasing molar content of Mo₅Si₃ and Mo₃Si, and therefore, the flammability limit determined for the reaction at Mo₅Si₃ or Mo₃Si/MgAl₂O₄ = 2.0. Based upon combustion wave kinetics, the activation energies, E_a = 68.8 and 63.8 kJ/mol, were deduced for the solid-state SHS reactions producing Mo₅Si₃– and Mo₃Si–MgAl₂O₄ composites, respectively. Phase conversion was almost complete after combustion, with the exception of trivial unreacted Mo existing in both composites and a minor amount of Mo₃Si in the Mo₅Si₃–MgAl₂O₄ composite. Both composites display a dense morphology formed by connecting MgAl₂O₄ crystals, within which micro-sized molybdenum silicide grains were embedded. For equimolar Mo₅Si₃– and Mo₃Si–MgAl₂O₄ composites, the hardness and fracture toughness are 14.6 GPa and 6.28 MPa m^1/2, and 13.9 GPa and 5.98 MPa m^1/2, respectively. Full article

(This article belongs to the Special Issue Intermetallics: Synthesis, Structure, Function)

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