Editorial

18 pages, 7679 KiB

Open AccessEditorial

The Critical Raw Materials Issue between Scarcity, Supply Risk, and Unique Properties

by Mihaela Girtan, Antje Wittenberg, Maria Luisa Grilli, Daniel P. S. de Oliveira, Chiara Giosuè and Maria Letizia Ruello

Materials 2021, 14(8), 1826; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14081826 - 07 Apr 2021

Cited by 22 | Viewed by 4685

Abstract

This editorial reports on a thorough analysis of the abundance and scarcity distribution of chemical elements and the minerals they form in the Earth, Sun, and Universe in connection with their number of neutrons and binding energy per nucleon. On one hand, understanding [...] Read more.

This editorial reports on a thorough analysis of the abundance and scarcity distribution of chemical elements and the minerals they form in the Earth, Sun, and Universe in connection with their number of neutrons and binding energy per nucleon. On one hand, understanding the elements’ formation and their specific properties related to their electronic and nucleonic structure may lead to understanding whether future solutions to replace certain elements or materials for specific technical applications are realistic. On the other hand, finding solutions to the critical availability of some of these elements is an urgent need. Even the analysis of the availability of scarce minerals from European Union sources leads to the suggestion that a wide-ranging approach is essential. These two fundamental assumptions represent also the logical approach that led the European Commission to ask for a multi-disciplinary effort from the scientific community to tackle the challenge of Critical Raw Materials. This editorial is also the story of one of the first fulcrum around which a wide network of material scientists gathered thanks to the support of the funding organization for research and innovation networks, COST (European Cooperation in Science and Technology). Full article

(This article belongs to the Special Issue Materials under Extreme Conditions: Technologies for CRMs Reduction, Substitution and Recovery)

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Research

Jump to: Editorial, Review

13 pages, 4012 KiB

Open AccessArticle

Microstructural Features in Multicore Cu–Nb Composites

by Elena N. Popova, Irina L. Deryagina, Evgeniya G. Valova-Zaharevskaya, Maria Letizia Ruello and Vladimir V. Popov, Jr.

Materials 2021, 14(22), 7033; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14227033 - 19 Nov 2021

Cited by 5 | Viewed by 1843

Abstract

The study is devoted to heavily drawn multicore Cu–18Nb composites of cylindrical and rectangular shapes. The composites were fabricated by the melt-and-deform method, namely, 600 in situ rods of Cu–18%Nb alloy were assembled in a copper shell and cold-drawn to a diameter of [...] Read more.

The study is devoted to heavily drawn multicore Cu–18Nb composites of cylindrical and rectangular shapes. The composites were fabricated by the melt-and-deform method, namely, 600 in situ rods of Cu–18%Nb alloy were assembled in a copper shell and cold-drawn to a diameter of 15.4 mm (e = 10.2) and then rolled into a rectangular shape the size of 3 × 5.8 mm (e = 12.5). The specimens were analyzed from the viewpoints of their microstructure, microhardness, and thermal stability. The methods of SEM, TEM, X-ray analysis, and microhardness measurements were applied. It is demonstrated that, at higher strain, the fiber texture

⟨110⟩ Nb ∥ ⟨111⟩ Cu ∥ DD

(drawing direction), characteristic of this material, becomes sharper. The distortions of niobium lattice can be observed, namely, the

\{110\}_{N b}

interplanar distance is broadened in longitudinal direction of specimens and compacted in transverse sections. The copper matrix lattice is distorted as well, though its distortions are much less pronounced due to its recrystallization. Evolution of microstructure under annealing consists mainly in the coagulation of ribbon-like Nb filaments and in the vanishing of lattice distortions. The structural changes in Nb filaments start at 300–400 °C, then develop actively at 600 °C and cause considerable decrease of strength at 700–800 °C. Full article

(This article belongs to the Special Issue Materials under Extreme Conditions: Technologies for CRMs Reduction, Substitution and Recovery)

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12 pages, 4313 KiB

Open AccessCommunication

Corrosion Resistance of Al–CNT Metal Matrix Composites

by Vladimir V. Popov, Alla Pismenny, Natalya Larianovsky, Anna Lapteva and Daniel Safranchik

Materials 2021, 14(13), 3530; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14133530 - 24 Jun 2021

Cited by 21 | Viewed by 2345

Abstract

The design of aluminium–graphite metal matrix composites (MMCs) with advanced mechanical properties and high corrosion resistance is in demand for aerospace, transportation, and industrial applications. Breakthroughs in this field are limited due to the tendency of aluminium–graphite MMCs to corrode. In the present [...] Read more.

The design of aluminium–graphite metal matrix composites (MMCs) with advanced mechanical properties and high corrosion resistance is in demand for aerospace, transportation, and industrial applications. Breakthroughs in this field are limited due to the tendency of aluminium–graphite MMCs to corrode. In the present research, aluminium-based MMCs were produced by a relatively novel combined two-staged method. Multiwall carbon nanotubes (MWCNTs) were added into molten Al1070 and processed by high-pressure die casting followed by cyclic extrusion. For the composites produced by this method, it was previously demonstrated that mechanical properties are improved in comparison with pure aluminium alloys. In the current study, the manufactured Al–MWCNT composites were investigated by electrochemical tests (such as open circuit potential), potentiodynamic tests, linear polarization tests, and electrochemical impedance spectra to understand the corrosion resistance of the obtained composite material. The experimental testing of the corrosion resistance of Al–MWCNT MMCs showed that due to the advantages of the fabrication method, the addition of CNTs to aluminium does not cause a radical decrease of corrosion resistance. Full article

(This article belongs to the Special Issue Materials under Extreme Conditions: Technologies for CRMs Reduction, Substitution and Recovery)

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23 pages, 7250 KiB

Open AccessArticle

Influence of Tool Geometry and Process Parameters on the Properties of Friction Stir Spot Welded Multiple (AA 5754 H111) Aluminium Sheets

by Danka Labus Zlatanovic, Sebastian Balos, Jean Pierre Bergmann, Stefan Rasche, Milan Pecanac and Saurav Goel

Materials 2021, 14(5), 1157; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14051157 - 01 Mar 2021

Cited by 12 | Viewed by 2715

Abstract

Friction stir spot welding is an emerging spot-welding technology that offers opportunities for joining a wide range of materials with minimum energy consumption. To increase productivity, the present work addresses production challenges and aims to find solutions for the lap-welding of multiple ultrathin [...] Read more.

Friction stir spot welding is an emerging spot-welding technology that offers opportunities for joining a wide range of materials with minimum energy consumption. To increase productivity, the present work addresses production challenges and aims to find solutions for the lap-welding of multiple ultrathin sheets with maximum productivity. Two convex tools with different edge radii were used to weld four ultrathin sheets of AA5754-H111 alloy each with 0.3 mm thickness. To understand the influence of tool geometries and process parameters, coefficient of friction (CoF), microstructure and mechanical properties obtained with the Vickers microhardness test and the small punch test were analysed. A scanning acoustic microscope was used to assess weld quality. It was found that the increase of tool radius from 15 to 22.5 mm reduced the dwell time by a factor of three. Samples welded with a specific tool were seen to have no delamination and improved mechanical properties due to longer stirring time. The rotational speed was found to be the most influential parameter in governing the weld shape, CoF, microstructure, microhardness and weld efficiency. Low rotational speeds caused a 14.4% and 12.8% improvement in joint efficiency compared to high rotational speeds for both tools used in this investigation. Full article

(This article belongs to the Special Issue Materials under Extreme Conditions: Technologies for CRMs Reduction, Substitution and Recovery)

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Review

Jump to: Editorial, Research

47 pages, 7416 KiB

Open AccessReview

Critical Raw Materials Saving by Protective Coatings under Extreme Conditions: A Review of Last Trends in Alloys and Coatings for Aerospace Engine Applications

by Maria Luisa Grilli, Daniele Valerini, Anca Elena Slobozeanu, Bogdan O. Postolnyi, Sebastian Balos, Antonella Rizzo and Radu Robert Piticescu

Materials 2021, 14(7), 1656; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14071656 - 28 Mar 2021

Cited by 28 | Viewed by 6854

Abstract

Several applications, where extreme conditions occur, require the use of alloys often containing many critical elements. Due to the ever increasing prices of critical raw materials (CRMs) linked to their high supply risk, and because of their fundamental and large utilization in high [...] Read more.

Several applications, where extreme conditions occur, require the use of alloys often containing many critical elements. Due to the ever increasing prices of critical raw materials (CRMs) linked to their high supply risk, and because of their fundamental and large utilization in high tech products and applications, it is extremely important to find viable solutions to save CRMs usage. Apart from increasing processes’ efficiency, substitution, and recycling, one of the alternatives to preserve an alloy and increase its operating lifetime, thus saving the CRMs needed for its manufacturing, is to protect it by a suitable coating or a surface treatment. This review presents the most recent trends in coatings for application in high temperature alloys for aerospace engines. CRMs’ current and future saving scenarios in the alloys and coatings for the aerospace engine are also discussed. The overarching aim of this paper is to raise awareness on the CRMs issue related to the alloys and coating for aerospace, suggesting some mitigation measures without having the ambition nor to give a complete overview of the topic nor a turnkey solution. Full article

(This article belongs to the Special Issue Materials under Extreme Conditions: Technologies for CRMs Reduction, Substitution and Recovery)

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17 pages, 3181 KiB

Open AccessReview

Complex Concentrated Alloys for Substitution of Critical Raw Materials in Applications for Extreme Conditions

by Dumitru Mitrica, Ioana Cristina Badea, Beatrice Adriana Serban, Mihai Tudor Olaru, Denisa Vonica, Marian Burada, Radu-Robert Piticescu and Vladimir V. Popov

Materials 2021, 14(5), 1197; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14051197 - 04 Mar 2021

Cited by 19 | Viewed by 3135

Abstract

The paper is proposing a mini-review on the capability of the new complex concentrated alloys (CCAs) to substitute or reduce the use of critical raw materials in applications for extreme conditions. Aspects regarding the regulations and expectations formulated by the European Union in [...] Read more.

The paper is proposing a mini-review on the capability of the new complex concentrated alloys (CCAs) to substitute or reduce the use of critical raw materials in applications for extreme conditions. Aspects regarding the regulations and expectations formulated by the European Union in the most recent reports on the critical raw materials were presented concisely. A general evaluation was performed on the CCAs concept and the research directions. The advantages of using critical metals for particular applications were presented to acknowledge the difficulty in the substitution of such elements with other materials. In order to establish the level of involvement of CCAs in the reduction of critical metal in extreme environment applications, a presentation was made of the previous achievements in the field and the potential for the reduction of critical metal content through the use of multi-component compositions. Full article

(This article belongs to the Special Issue Materials under Extreme Conditions: Technologies for CRMs Reduction, Substitution and Recovery)

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21 pages, 6293 KiB

Open AccessReview

Development of TiAl–Si Alloys—A Review

by Anna Knaislová, Pavel Novák, Marcello Cabibbo, Lucyna Jaworska and Dalibor Vojtěch

Materials 2021, 14(4), 1030; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14041030 - 22 Feb 2021

Cited by 19 | Viewed by 4027

Abstract

This paper describes the effect of silicon on the manufacturing process, structure, phase composition, and selected properties of titanium aluminide alloys. The experimental generation of TiAl–Si alloys is composed of titanium aluminide (TiAl, Ti₃Al or TiAl₃) matrix reinforced by [...] Read more.

This paper describes the effect of silicon on the manufacturing process, structure, phase composition, and selected properties of titanium aluminide alloys. The experimental generation of TiAl–Si alloys is composed of titanium aluminide (TiAl, Ti₃Al or TiAl₃) matrix reinforced by hard and heat-resistant titanium silicides (especially Ti₅Si₃). The alloys are characterized by wear resistance comparable with tool steels, high hardness, and very good resistance to oxidation at high temperatures (up to 1000 °C), but also low room-temperature ductility, as is typical also for other intermetallic materials. These alloys had been successfully prepared by the means of powder metallurgical routes and melting metallurgy methods. Full article

(This article belongs to the Special Issue Materials under Extreme Conditions: Technologies for CRMs Reduction, Substitution and Recovery)

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37 pages, 2608 KiB

Open AccessReview

Powder Bed Fusion Additive Manufacturing Using Critical Raw Materials: A Review

by Vladimir V. Popov, Maria Luisa Grilli, Andrey Koptyug, Lucyna Jaworska, Alexander Katz-Demyanetz, Damjan Klobčar, Sebastian Balos, Bogdan O. Postolnyi and Saurav Goel

Materials 2021, 14(4), 909; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14040909 - 14 Feb 2021

Cited by 64 | Viewed by 9742

Abstract

The term “critical raw materials” (CRMs) refers to various metals and nonmetals that are crucial to Europe’s economic progress. Modern technologies enabling effective use and recyclability of CRMs are in critical demand for the EU industries. The use of CRMs, especially in the [...] Read more.

The term “critical raw materials” (CRMs) refers to various metals and nonmetals that are crucial to Europe’s economic progress. Modern technologies enabling effective use and recyclability of CRMs are in critical demand for the EU industries. The use of CRMs, especially in the fields of biomedicine, aerospace, electric vehicles, and energy applications, is almost irreplaceable. Additive manufacturing (also referred to as 3D printing) is one of the key enabling technologies in the field of manufacturing which underpins the Fourth Industrial Revolution. 3D printing not only suppresses waste but also provides an efficient buy-to-fly ratio and possesses the potential to entirely change supply and distribution chains, significantly reducing costs and revolutionizing all logistics. This review provides comprehensive new insights into CRM-containing materials processed by modern additive manufacturing techniques and outlines the potential for increasing the efficiency of CRMs utilization and reducing the dependence on CRMs through wider industrial incorporation of AM and specifics of powder bed AM methods making them prime candidates for such developments. Full article

(This article belongs to the Special Issue Materials under Extreme Conditions: Technologies for CRMs Reduction, Substitution and Recovery)

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36 pages, 7264 KiB

Open AccessReview

Solutions of Critical Raw Materials Issues Regarding Iron-Based Alloys

by Pavel Novák, Tiziano Bellezze, Marcello Cabibbo, Ernst Gamsjäger, Manfred Wiessner, Dragan Rajnovic, Lucyna Jaworska, Pavel Hanus, Andrei Shishkin, Gaurav Goel and Saurav Goel

Materials 2021, 14(4), 899; https://0-doi-org.brum.beds.ac.uk/10.3390/ma14040899 - 13 Feb 2021

Cited by 5 | Viewed by 4343

Abstract

The Critical Raw Materials (CRMs) list has been defined based on economic importance and supply risk by the European Commission. This review paper describes two issues regarding critical raw materials: the possibilities of their substitution in iron-based alloys and the use of iron-based [...] Read more.

The Critical Raw Materials (CRMs) list has been defined based on economic importance and supply risk by the European Commission. This review paper describes two issues regarding critical raw materials: the possibilities of their substitution in iron-based alloys and the use of iron-based alloys instead of other materials in order to save CRMs. This review covers strategies for saving chromium in stainless steel, substitution or lowering the amounts of carbide-forming elements (especially tungsten and vanadium) in tool steel and alternative iron-based CRM-free and low-CRM materials: austempered ductile cast iron, high-temperature alloys based on intermetallics of iron and sintered diamond tools with an iron-containing low-cobalt binder. Full article

(This article belongs to the Special Issue Materials under Extreme Conditions: Technologies for CRMs Reduction, Substitution and Recovery)

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