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Special Issue "High-Entropy Alloy Coatings and Surface Functionalization"

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A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Corrosion, Wear and Erosion".

Deadline for manuscript submissions: closed (10 July 2023) | Viewed by 9296

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Dr. Thomas Lindner

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Guest Editor

Materials and Surface Engineering Group, Institute of Materials Science and Engineering, Chemnitz University of Technology, 09107 Chemnitz, Germany
Interests: high-entropy alloys; coatings; thermal spraying; laser-cladding; thermochemical treatment; spark plasma sintering; additive manufacturing

Special Issue Information

Dear Colleagues,

High-entropy alloys (HEAs) offer a wide range of research and development potential due to their outstanding properties. The limited material usage for surface technology especially promises a sustainable and demand-oriented ecological and economical use of these high-performance materials. The development of suitable processing methods for coating technologies, heat treatment, as well as mechanical finishing routines enables new system solutions in the area of complex surface stresses. The large number of potential processing technologies enables the realization of coating systems for different scale ranges. Mechanical finishing and modification of the surface by thermochemical processes are additional possibilities to adjust the functional properties of coating systems. However, there is still a great need for a profound understanding of the process–microstructure–property relationships. The central focus of this Special Issue is on current development trends for HEAs in the fields of casting, powder metallurgy, additive manufacturing, and coating technology, as well as surface functionalization and finishing.

In particular, the topics of interest include but are not limited to:

Casting and powder metallurgical manufacturing;
Coating processes (e.g., thermal spraying, laser cladding and magnetron sputter deposition);
Additive manufacturing and spark plasma sintering;
Mechanical finishing and plasma polishing;
Heat treatment and thermochemical surface hardening;
Computational modeling and simulation.

Dr. Thomas Lindner
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Published Papers (7 papers)

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Research

Open AccessArticle

Influence of Milling Conditions on Al_xCoCrFeNiMo_y Multi-Principal-Element Alloys

and

Coatings 2023, 13(3), 662; https://doi.org/10.3390/coatings13030662 - 22 Mar 2023

Viewed by 751

Abstract

Multi-Principal-Element or High-Entropy Alloys (MPEAs/HEAs) have gained increasing interest in the past two decades largely due to their outstanding properties such as superior mechanical strength and corrosion resistance. However, research studies on their processability are still scarce. This work assesses the effect of different machining conditions on the machinability of these novel alloys, with the objective of advancing the introduction of MPEA systems into industrial applications. The present study focuses on the experimental analysis of finish-milling conditions and their effects on the milling process and resulting surface finish of CoCrFeNi, Al_0.3CoCrFeNi and Al_0.3CoCrFeNiMo_0.2 alloys fabricated via Spark Plasma Sintering. Ball-nose-end milling experiments have been carried out various milling parameters such as cutting speed, feed per cutting edge, and ultrasonic assistance. In situ measurements of cutting forces and temperature on the tool edge were performed during the experiments, and surface finish and tool wear were analyzed afterwards. The results exhibited decreasing cutting forces by means of low feed per cutting edge and reduced process temperatures at low cutting speed, with the use of ultrasonic-assisted milling. It was shown that the machinability of these modern alloys through conventional, as well as modern machining methods such as ultrasonic-assisted milling, is viable, and common theories in machining can be transferred to these novel MPEAs. Full article

(This article belongs to the Special Issue High-Entropy Alloy Coatings and Surface Functionalization)

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Open AccessArticle

Microstructure Evolution and Wear Resistance of the Eutectic High-Entropy Alloy Al_0.3CoCrFeNiNb_0.5 Produced by Laser Metal Deposition

Bianca Preuß

Thomas Lindner

Thomas Uhlig

Jorge Eduardo Tapia Cabrera

and

Coatings 2023, 13(3), 585; https://doi.org/10.3390/coatings13030585 - 08 Mar 2023

Cited by 1 | Viewed by 1095

Abstract

Eutectic high-entropy alloys (EHEAs) are characterized by a fine lamellar microstructure. This allows for homogeneous functional surface properties. Furthermore, the risk of coarse precipitate formation during coating processes from the liquid state is avoided. However, the influence of the size and the texture of the local microstructure domain on functional properties is still unknown. The present work is devoted to the microstructural evolution of the EHEA Al_0.3CoCrFeNiNb_0.5. Inert gas atomized powder was processed by laser metal deposition (LMD) and spark plasma sintering (SPS). Both specimens were heat treated near their liquidus temperatures. The different production routes have a decisive influence on the orientation of the lamellar structure. The SPS bulk material has a statistically distributed orientation of the lamellae defined by the microstructure of the powder. However, the remelting of the powder during the LMD process causes a directional vertical solidification of the lamellar structure. Based on these differences, positive effects on their functional properties were detected for directionally solidified LMD coatings. As a result of the heat treatment, the influence of the lamellar orientation on their tribological properties is reduced, whereas the influence of the lamellar size on their property profile can be derived. Full article

(This article belongs to the Special Issue High-Entropy Alloy Coatings and Surface Functionalization)

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Open AccessArticle

Non-Metallic Alloying Constituents to Develop a Wear-Resistant CrFeNi-BSiC High-Entropy Alloy for Surface Protective Coatings by Thermal Spraying and High-Speed Laser Metal Deposition

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Coatings 2023, 13(2), 291; https://doi.org/10.3390/coatings13020291 - 27 Jan 2023

Cited by 1 | Viewed by 1001

Abstract

Compositional alterations to high-entropy alloys (HEAs) allow further evolution of these materials by adjusting their property profiles. This way, they can be used for coating technologies and surface-protection applications. In the present work, minor quantities of the non-metallic alloying constituents, BSiC, were added to the CrFeNi base system. The alloy development was carried out in an electric arc furnace in comparison with the nickel-based alloy Ni-600. With regard to the BSiC-free variant, the wear resistance can be significantly increased. The powder was manufactured by inert gas atomization and characterized, followed by processing via high-velocity oxy-fuel spraying (HVOF) and high velocity laser metal deposition (HS-LMD). Depending on the manufacturing conditions, the proportion and shape of the precipitates within the microstructure differ. Compared to both the reference system and the as-cast condition, the coating systems demonstrated comparable or improved resistance to wear. The evaluation of the process–structure–property relationships confirmed the great potential of developing load-adapted HEA systems using non-metallic alloy constituents in the field of surface engineering. Full article

(This article belongs to the Special Issue High-Entropy Alloy Coatings and Surface Functionalization)

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Open AccessArticle

Nb and Mo Influencing the High-Temperature Wear Behavior of HVOF-Sprayed High-Entropy Alloy Coatings

Lisa-Marie Rymer

Thomas Lindner

and

Thomas Lampke

Coatings 2023, 13(1), 9; https://doi.org/10.3390/coatings13010009 - 21 Dec 2022

Cited by 1 | Viewed by 886

Abstract

To qualify high-entropy alloys (HEAs) as resource-saving and high-temperature wear-resistant coating materials, high-velocity oxygen fuel (HVOF) coatings produced from the inert gas-atomized powder of Al_0.3CrFeCoNi, Al_0.3CrFeCoNiNb_0.5 and Al_0.3CrFeCoNiMo_0.75 were investigated in reciprocating wear tests at temperatures at 25, 500, 700 and 900 °C. In addition to the high-temperature wear tests, the microstructure and chemical composition of the three HEAs were analyzed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). In particular, HVOF coatings are characterized by high hardness (Vickers hardness HV0.1) and low porosity, which were also determined. After high-temperature wear tests, the wear depth was measured using laser scanning microscopy (LSM). It was found that adding Nb and Mo to Al_0.3CrFeCoNi significantly reduces the wear depth with increasing temperature. The wear mechanisms change from abrasive wear and delamination (25 °C and 500 °C) to a combination of (abrasion), delamination, adhesion and oxidative wear. Thereby, oxidative wear will be the primary mechanism at 900 °C for all the HVOF coatings investigated. The most important finding is that the adhesion of the oxide layer formed is improved by adding Nb and Mo, resulting in significantly reduced wear depth at 900 °C. Full article

(This article belongs to the Special Issue High-Entropy Alloy Coatings and Surface Functionalization)

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Open AccessCommunication

High-Speed Laser Metal Deposition of CrFeCoNi and AlCrFeCoNi HEA Coatings with Narrow Intermixing Zone and their Machining by Turning and Diamond Smoothing

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Coatings 2022, 12(7), 879; https://doi.org/10.3390/coatings12070879 - 21 Jun 2022

Cited by 6 | Viewed by 1094

Abstract

The processing of high-entropy alloys (HEAs) via laser metal deposition (LMD) is well known. However, it is still difficult to avoid chemical intermixing of the elements between the coating and the substrate. Therefore, the produced coatings do not have the same chemical composition as the HEA feedstock material. Single-layer CrFeCoNi and AlCrFeCoNi HEA coatings were deposited using high-speed laser metal deposition (HS-LMD). Elemental mapping confirmed a good agreement with the chemical composition of the powder feedstock material, and revealed that chemical intermixing was confined to the immediate substrate interface. The coatings are characterized by a homogeneous structure with good substrate bonding. The machining of these coatings via turning is possible. Subsequent diamond smoothing results in a strong decrease in the surface roughness. This study presents a complete manufacturing chain for the production of high-quality HS-LMD HEA coatings. Full article

(This article belongs to the Special Issue High-Entropy Alloy Coatings and Surface Functionalization)

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Open AccessArticle

Hardness Enhancement in CoCrFeNi_1−x(WC)_x High-Entropy Alloy Thin Films Synthesised by Magnetron Co-Sputtering

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Coatings 2022, 12(2), 269; https://doi.org/10.3390/coatings12020269 - 17 Feb 2022

Viewed by 1471

Abstract

We demonstrate the systematic hardness enhancement of the CoCrFeNi high-entropy alloy (HEA) by the addition of tungsten carbide (WC). Mixed thin films are fabricated by magnetron co-sputtering using a home-made spark plasma-sintered CoCrFeNi target and a commercially available WC target. The WC content in the thin films is adjusted via the ratio of deposition powers applied to the targets. X-ray photoelectron spectroscopy (XPS) and energy dispersive X-ray spectroscopy (EDX) measurements were taken to determine the surface and bulk stoichiometry, respectively. The uniform distribution of the elements is confirmed via EDX mapping. X-ray diffraction (XRD) is carried out on the samples to determine the crystal phase formation. The Vickers hardness of the thin films is investigated using nanoindentation and shows an increase in the hardness in the thin films following an increased WC content. The data obtained are presented in comparison to pure WC and CoCrFeNi thin films fabricated by magnetron sputtering, respectively. Full article

(This article belongs to the Special Issue High-Entropy Alloy Coatings and Surface Functionalization)

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Open AccessArticle

Vertical Graphene Growth on AlCu4Mg Alloy by PECVD Technique

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Coatings 2021, 11(9), 1108; https://doi.org/10.3390/coatings11091108 - 14 Sep 2021

Cited by 3 | Viewed by 1784

Abstract

Vertical graphene, which belongs to nanomaterials, is a very promising tool for improving the useful properties of long-used and proven materials. Since the growth of vertical graphene is different on each base material and has specific deposition setting parameters, it is necessary to examine each base material separately. For this reason, a full factor design of experiment was performed with 2⁶ = 64 rounds, which contained additional 5 central points, i.e., a total of 69 rounds of individual experiments, which was to examine the effect of input factors Temperature, Pressure, Flow, CH₄, Plasma Power, and Annealing in H₂ on the growth of vertical graphene on aluminum alloy AlCu4Mg. The deposition was performed using plasma-enhanced chemical vapor deposition (PECVD) technology. Mainly, the occurrence of graphene was analyzed, which was confirmed by Raman spectroscopy, as well as its thickness. The characterization was performed using electron and transmission microscopy, including an atomic force microscope. It was found that the growth of graphene occurred in 7 cases and its thickness is affected only by the interaction flow (sccm) × pretreatment H₂ (sccm). Full article

(This article belongs to the Special Issue High-Entropy Alloy Coatings and Surface Functionalization)

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