Ceramic Coatings for High-Temperature Applications

A special issue of Ceramics (ISSN 2571-6131).

Deadline for manuscript submissions: closed (30 April 2023) | Viewed by 29827

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Guest Editor
Coating Department, FunGlass - Centre for Functional and Surface Functionalised Glass, Alexander Dubcek University of Trencin, 91150 Trencin, Slovakia
Interests: thermal barrier coatings; hot corrosion; splat morphology; ceramic and metallic composite; high entropy alloys

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Guest Editor
Department of Coating Processes, Centre for Functional and Surface Functionalized Glass, Alexander Dubček University of Trenčín, Študentská 2, 911 50 Trenčín, Slovakia
Interests: thin films; coatings; ceramics; thermal barrier coatings; coatings on bioimplants; corrosion; diffusion barrier coatings; geopolymer coatings; PVD coatings; PECVD
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Special Issue Information

Dear Colleagues,

High-temperature ceramic coatings, as we know, are gaining popularity in industries such as the aeronautics, chemical and petrochemical, fossil or renewable energy generation, and automotive industries because they provide an ideal option for providing thermal insulation and preventing deterioration and corrosion in harsh conditions.

Ceramic coatings are frequently used on metallic components to offer thermal shock protection, surface seals, erosion protection, diffusion barriers, sealants, and thermal insulation. Understanding the microstructure and behavior of ceramic coatings is critical for optimizing their functioning. Durability, ease of application, repairability, reliability, and long-term performance are all critical characteristics of such coatings. As such, this Special Issue will feature research and review articles on ceramic (for example, ZrO2, Al2O3, SiC, SiO2, HfC, TaC, and ZrC) and composite coatings used in high-temperature environments, as well as the factors influencing their selection and processing. Along with ceramic coatings, cermet-based coatings for use in high-temperature situations are also welcome.

This is a great opportunity for the high-temperature-coatings research community since it could lead to several applications in which ceramic coatings can improve the efficiency and longevity of coated metallic components.

Dr. Amirhossein Pakseresht
Dr. A. M. Kamalan Kirubaharan
Guest Editors

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Keywords

  • thermal barrier coatings
  • ultra-high-temperature ceramic coatings
  • hot corrosion
  • plasma spraying
  • oxidation
  • erosion
  • wear
  • thermal protection
  • thermal spray coatings

Published Papers (16 papers)

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13 pages, 13425 KiB  
Article
Comparative Study of Mechanical Performance of AlCrSiN Coating Deposited on WC-Co and cBN Hard Substrates
by Jing Liang, Marc Serra, Sandra Gordon, Jonathan Fernández de Ara, Eluxka Almandoz, Luis Llanes and Emilio Jimenez-Piqué
Ceramics 2023, 6(2), 1238-1250; https://doi.org/10.3390/ceramics6020075 - 09 Jun 2023
Cited by 1 | Viewed by 1336
Abstract
The objective of this study is to explore and compare the mechanical response of AlCrSiN coatings deposited on two different substrates, namely, WC-Co and cBN. Nano-indentation was used to measure the hardness and elastic modulus of the coatings, and micro-indentation was used for [...] Read more.
The objective of this study is to explore and compare the mechanical response of AlCrSiN coatings deposited on two different substrates, namely, WC-Co and cBN. Nano-indentation was used to measure the hardness and elastic modulus of the coatings, and micro-indentation was used for observing the contact damage under Hertzian contact with monotonic and cyclic (fatigue) loads. Microscratch and contact damage tests were also used to evaluate the strength of adhesion between the AlCrSiN coatings and the two substrates under progressive and constant loads, respectively. The surface damages induced via different mechanical tests were observed using scanning electron microscopy (SEM). A focused ion beam (FIB) was used to produce a cross-section of the coating–substrate system in order to further detect the mode and extent of failure that was induced. The results show that the AlCrSiN coating deposited on the WC-Co substrate performed better in regard to adhesion strength and contact damage response than the same coating deposited on the cBN substrate; this is attributed to the lower plasticity of the cBN substrate as well as its less powerful adhesion to the coating. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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11 pages, 4067 KiB  
Article
Structural-Phase Change of Multilayer Ceramics Zr-Y-O/Si-Al-N under High Temperature
by Marina Fedorischeva, Mark Kalashnikov, Irina Bozhko, Tamara Dorofeeva and Victor Sergeev
Ceramics 2023, 6(2), 1227-1237; https://doi.org/10.3390/ceramics6020074 - 08 Jun 2023
Viewed by 1034
Abstract
To increase the thermocyclic resistance of material, multilayer coatings with alternating layers of Zr-Y-O and Si-Al-N were obtained via magnetron sputtering. It was established that a coating layer based on Zr-Y-O has a columnar structure; the height of the columns is determined by [...] Read more.
To increase the thermocyclic resistance of material, multilayer coatings with alternating layers of Zr-Y-O and Si-Al-N were obtained via magnetron sputtering. It was established that a coating layer based on Zr-Y-O has a columnar structure; the height of the columns is determined by the thickness of the layer. The Si-Al-N-based layer is amorphous. There were monoclinic and tetragonal phases with a large lattice parameter in the composition of the Zr-Y-O-based coating layer. After high-temperature annealing, a tetragonal phase with a small lattice parameter appeared in the microscope column. In the “in situ” mode, a change in the structural state of the Zr-Y-O coating layer was detected in the temperature range of 450–500 °C; namely, a change in the grain size and coherent scattering regions, and an increase in internal elastic stresses. It was found that the thermocyclic resistance increased by more than two times for multilayer samples compared to the single-layer ones we studied earlier. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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17 pages, 26680 KiB  
Article
On the Statistics of Mechanical Failure in Flame-Sprayed Self-Supporting Components
by Florian Kerber, Magda Hollenbach, Marc Neumann, Tony Wetzig, Thomas Schemmel, Helge Jansen and Christos G. Aneziris
Ceramics 2023, 6(2), 1050-1066; https://doi.org/10.3390/ceramics6020062 - 25 Apr 2023
Cited by 4 | Viewed by 1442
Abstract
The objective of this study was to investigate the variability of flexural strength for flame-sprayed ceramic components and to determine which two-parametric distribution function was best suited to represent the experimental data. Moreover, the influence of the number of tested specimens was addressed. [...] Read more.
The objective of this study was to investigate the variability of flexural strength for flame-sprayed ceramic components and to determine which two-parametric distribution function was best suited to represent the experimental data. Moreover, the influence of the number of tested specimens was addressed. The stochastic nature of the flame-spraying process causes a pronounced variation in the properties of potential components, making it crucial to characterise the fracture statistics. To achieve this, this study used two large data sets consisting of 1000 flame-sprayed specimens each. In addition to the standard Weibull approach, the study examined the quality of representing the experimental data using other two-parametric distribution functions (Normal, Log-Normal, and Gamma). To evaluate the accuracy of the distribution functions and their characteristic parameters, random subsamples were generated by resampling of the experimental data, and the results were assessed based on the sampling size. It was found that the experimental data were best represented by either the Weibull or Gamma distribution, and the quality of the fit was correlated with the number of positive and negative outliers. The Weibull fit was more sensitive to positive outliers, whereas the Gamma fit was more sensitive to negative outliers. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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10 pages, 1773 KiB  
Article
Thermal Fracture of Functionally Graded Coatings with Systems of Cracks: Application of a Model Based on the Rule of Mixtures
by Vera Petrova, Siegfried Schmauder and Alexandros Georgiadis
Ceramics 2023, 6(1), 255-264; https://doi.org/10.3390/ceramics6010015 - 11 Jan 2023
Cited by 3 | Viewed by 1294
Abstract
This paper is devoted to the problem of the thermal fracture of a functionally graded coating (FGC) on a homogeneous substrate (H), i.e., FGC/H structures. The FGC/H structure was subjected to thermo-mechanical loadings. Systems of interacting cracks were located in the FGC. Typical [...] Read more.
This paper is devoted to the problem of the thermal fracture of a functionally graded coating (FGC) on a homogeneous substrate (H), i.e., FGC/H structures. The FGC/H structure was subjected to thermo-mechanical loadings. Systems of interacting cracks were located in the FGC. Typical cracks in such structures include edge cracks, internal cracks, and edge/internal cracks. The material properties and fracture toughness of the FGC were modeled by formulas based on the rule of mixtures. The FGC comprised two constituents, a ceramic on the top and a metal as a homogeneous substrate, with their volume fractions determined by a power law function with the power coefficient λ as the gradation parameter for the FGC. For this study, the method of singular integral equations was used, and the integral equations were solved numerically by the mechanical quadrature method based on the Chebyshev polynomials. Attention was mainly paid to the determination of critical loads and energy release rates for the systems of interacting cracks in the FGCs in order to find ways to increase the fracture resistance of FGC/H structures. As an illustrative example, a system of three edge cracks in the FGC was considered. The crack shielding effect was demonstrated for this system of cracks. Additionally, it was shown that the gradation parameter λ had a great effect on the fracture characteristics. Thus, the proposed model provided a sound basis for the optimization of FGCs in order to improve the fracture resistance of FGC/H structures. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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10 pages, 2532 KiB  
Article
Increasing the Flow Stress during High-Temperature Deformation of Aluminum Matrix Composites Reinforced with TiC-Coated CNTs
by Artemiy V. Aborkin, Dmitriy V. Bokaryov, Sergey A. Pankratov and Alexey I. Elkin
Ceramics 2023, 6(1), 231-240; https://doi.org/10.3390/ceramics6010013 - 10 Jan 2023
Cited by 2 | Viewed by 1323
Abstract
In this work, composites based on AA5049 aluminium alloy reinforced with multiwalled carbon nanotubes (CNTs) and multiwalled TiC-coated CNTs were prepared by powder metallurgy. For the first time, the effect of TiC coating on the CNT surface on the flow stress of aluminum [...] Read more.
In this work, composites based on AA5049 aluminium alloy reinforced with multiwalled carbon nanotubes (CNTs) and multiwalled TiC-coated CNTs were prepared by powder metallurgy. For the first time, the effect of TiC coating on the CNT surface on the flow stress of aluminum matrix composites under compressive conditions at 300–500 °C has been investigated. It was found that composites reinforced with TiC-coated CNTs have a higher flow stress during high-temperature deformation compared to composites reinforced with uncoated CNTs. Moreover, with an increasing temperature in the 300–500 °C range, the strengthening effect increases from 14% to 37%. Compared to the reference sample of the matrix material without reinforcing particles, obtained by the same technological route, the composites reinforced with CNTs and CNT-hybrid structures had a 1.8–2.9 times higher flow stress during high-temperature deformation. The presented results show that the modification of the CNTs surface with ceramic nanoparticles is a promising structure design strategy that improves the heat resistance of aluminum matrix composites. This extends the potential range of application of aluminum matrix composites as a structural material for operation at elevated temperatures. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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22 pages, 5104 KiB  
Article
Optimization of Plasma Electrolytic Oxidation Technological Parameters of Deformed Aluminum Alloy D16T in Flowing Electrolyte
by Liubomyr Ropyak, Thaer Shihab, Andrii Velychkovych, Vitalii Bilinskyi, Volodymyr Malinin and Mykola Romaniv
Ceramics 2023, 6(1), 146-167; https://doi.org/10.3390/ceramics6010010 - 10 Jan 2023
Cited by 14 | Viewed by 1966
Abstract
The prospects of plasma electrolytic oxidation (PEO) technology applied for surface hardening of aluminum alloys are substantiated. The work aims to optimize the technological process of PEO for aluminum in flowing electrolyte. The design of the equipment and the technological process of the [...] Read more.
The prospects of plasma electrolytic oxidation (PEO) technology applied for surface hardening of aluminum alloys are substantiated. The work aims to optimize the technological process of PEO for aluminum in flowing electrolyte. The design of the equipment and the technological process of the PEO for aluminum deformed alloy D16T in flowing silicate–alkaline electrolyte have been developed. Oxide coatings were formed according to various technological parameters of the PEO process. The properties of the oxide coatings were evaluated, respectively, by measurements of coating thickness, geometric dimensions of the samples, microhardness, wear tests, and optical and scanning electron microscopy. To study the influence of the technological parameters of the PEO process of forming oxide coatings on geometrical, physical, and mechanical properties, planning of the experiment was used. According to the results of the conducted experiments, a regression equation of the second order was obtained and the response surfaces were constructed. We determined the optimal values of the technological parameters of the PEO process: component concentration ratio (Na2SiO3/KOH), current density, flow rate, and electrolyte temperature, which provide the oxide coating with minimal wear and sufficiently high physical and mechanical properties and indicators of the accuracy of the shape of the parts. The research results showed that the properties of oxide coatings mainly depend on almost all constituent modes of the PEO process. Samples with Al2O3 oxide coating were tested during dry friction according to the “ring–ring” scheme. It was established that the temperature in the friction zone of aluminum samples with an oxide coating is lower compared to steel samples without a coating, and this indicates high frictional heat resistance of the oxide coating. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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13 pages, 5153 KiB  
Article
Tensile Adhesion Strength of Atmospheric Plasma Sprayed MgAl2O4, Al2O3 Coatings
by Andrey Zayatzev, Albina Lukianova, Dmitry Demoretsky and Yulia Alexandrova
Ceramics 2022, 5(4), 1242-1254; https://doi.org/10.3390/ceramics5040088 - 09 Dec 2022
Cited by 5 | Viewed by 1416
Abstract
This study analyses the distribution of stress during the testing of glued cylindrical specimens with thermally sprayed MgAl2O4, Al2O3 oxide coatings in order to evaluate the tensile adhesion strength. The set of studies that make up [...] Read more.
This study analyses the distribution of stress during the testing of glued cylindrical specimens with thermally sprayed MgAl2O4, Al2O3 oxide coatings in order to evaluate the tensile adhesion strength. The set of studies that make up this work were conducted in order to evaluate the influence of the geometric parameters of cylindrical test specimens, 25 mm in diameter by 16–38.1 mm in height, on the measured tensile adhesion strength of the specimens. The stress and strain states inside the coating and at the coating-substrate interface were determined using the finite element modelling method. The debonding mechanisms, failure mode and influence of the coating microstructure on bond strength are also discussed. The finite element stress analysis shows a significant level of non-uniform stress distribution in the test specimens. The analysis of the results of the modelling stresses and strains using the finite element method for six types of cylindrical specimens, as well as the values obtained for the adhesion testing of MgAl2O4, Al2O3 coatings, show a need to increase the height of the standard cylindrical specimen (according to ASTM C633-13 (2021), GOST 9.304-87). The height should be increased by no less than 1.5–2.0 times to reduce the level of a non-uniform stress distribution in the separation area. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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18 pages, 10048 KiB  
Article
Comparative Study on the Scratch and Wear Resistance of Diamond-like Carbon (DLC) Coatings Deposited on X42Cr13 Steel of Different Surface Conditions
by Shiraz Ahmed Siddiqui and Maria Berkes Maros
Ceramics 2022, 5(4), 1207-1224; https://doi.org/10.3390/ceramics5040086 - 08 Dec 2022
Cited by 1 | Viewed by 2213
Abstract
Tribological investigations are of great importance, especially in the case of novel combinations of materials used for the tribosystem. In the current research, multilayer diamond-like carbon coating deposited by plasma enhanced chemical vapour deposition on an X42Cr13 plastic mould tool steel is studied [...] Read more.
Tribological investigations are of great importance, especially in the case of novel combinations of materials used for the tribosystem. In the current research, multilayer diamond-like carbon coating deposited by plasma enhanced chemical vapour deposition on an X42Cr13 plastic mould tool steel is studied with two different surface conditions of the substrate. On the one hand, it is secondary hardened; on the other hand, it is additively plasma nitrided preceding the diamond-like carbon coating. This latter combined treatment, called duplex treatment, has an increasingly wide range of applications today. However, its effectiveness largely depends on applying the appropriate nitriding technology. The tribological behaviour was characterised by an instrumented scratch test and a reciprocating ball-on-plate wear test. The results demonstrate better scratch resistance for the duplex-treated samples, while they show weaker performance in the applied wear type of loading. The current comparative study reveals the reason for the unexpected behaviour and highlights some critical aspects of the heat treatment procedure. The architecture of the tested multilayer DLC coating is unique, and no tribological results have yet been published on tribosystems combined with an X42Cr13 steel substrate. The presented results may particularly interest tribologists and the materials research community. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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26 pages, 7825 KiB  
Article
Structural, Optical, Magnetic and Electrical Properties of Sputtered ZnO and ZnO:Fe Thin Films: The Role of Deposition Power
by Ahmed Faramawy, Hamada Elsayed, Carlo Scian and Giovanni Mattei
Ceramics 2022, 5(4), 1128-1153; https://doi.org/10.3390/ceramics5040080 - 01 Dec 2022
Cited by 11 | Viewed by 1914
Abstract
Structural, optical, magnetic, and electrical properties of zinc oxide (henceforth, ZO) and iron doped zinc oxide (henceforth, ZOFe) films deposited by sputtering technique are described by means of Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, scanning electron microscope (SEM), UV–Vis spectrometer, vibrating sample [...] Read more.
Structural, optical, magnetic, and electrical properties of zinc oxide (henceforth, ZO) and iron doped zinc oxide (henceforth, ZOFe) films deposited by sputtering technique are described by means of Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, scanning electron microscope (SEM), UV–Vis spectrometer, vibrating sample magnetometer, and room temperature electrical conductivity, respectively. GIXRD analysis revealed that the films were polycrystalline with a hexagonal phase, and all films had a preferred (002) c-axis orientation. The lattice parameters a and c of the wurtzite structure were calculated for all films. The a parameter remains almost the same (around 3 Å), while c parameter varies slightly with increasing Fe content from 5.18 to 5.31 Å throughout the co-deposition process. The optical gap for undoped and doped ZO was obtained from different numerical methods based on the experimental data and it was increased with the increment of the concentration of Fe dopant from 3.26 eV to 3.35 eV. The highest magnetization (4.26 × 10−4 emu/g) and lowest resistivity (4.6 × 107 Ω·cm) values of the ZO films were found to be at an Fe content of 5% at. %. An explanation for the dependence of the optical, magnetic, and electrical properties of the samples on the Fe concentrations is also given. The enhanced magnetic properties such as saturated magnetization and coercivity with optical properties reveal that Fe doped ZO thin films are suitable for magneto-optoelectronic (optoelectronic and spintronics) device applications. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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18 pages, 7516 KiB  
Article
Tribological Study of Simply and Duplex-Coated CrN-X42Cr13 Tribosystems under Dry Sliding Wear and Progressive Loading Scratching
by Maria Berkes Maros and Shiraz Ahmed Siddiqui
Ceramics 2022, 5(4), 1084-1101; https://doi.org/10.3390/ceramics5040077 - 24 Nov 2022
Viewed by 1607
Abstract
CrN coatings are widely used in the industry due to their excellent mechanical features and outstanding wear and corrosion resistance. Using scratch and ball-on-disk wear tests, the current study deals with the tribological characterisation of CrN coatings deposited onto an X42Cr13 plastic mould [...] Read more.
CrN coatings are widely used in the industry due to their excellent mechanical features and outstanding wear and corrosion resistance. Using scratch and ball-on-disk wear tests, the current study deals with the tribological characterisation of CrN coatings deposited onto an X42Cr13 plastic mould tool steel. Two surface conditions of the secondary-hardened substrate are compared—the plasma nitrided (duplex treated) and the un-nitrided (simply coated) states. The appropriate combination of secondary hardening providing the maximum toughness and the high-temperature nitriding of this high Cr steel is a great challenge due to the nitrogen-diffusion-inhibiting effect of Cr. The beneficial effect of the applied duplex treatment is proven by the 34% improvement of the adhesion strength and the 43% lower wear rate of the investigated duplex coatings. Detailed morphological analyses give insight into the characteristic damage mechanisms controlling the coating failure processes during scratching and wearing. For the simply CrN-coated sample, a new type of scratch damage mechanism, named “SAS-wings”, is identified, providing useful information in predicting the final failure of the coating. The tribological results obtained on tribosystems with the investigated high Cr steel/CrN constituents represent a novelty in the given field. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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14 pages, 6100 KiB  
Article
Characterization of Thermal Barrier Coatings Using an Active Thermography Approach
by Francesca Curà, Raffaella Sesana, Luca Corsaro and Riccardo Mantoan
Ceramics 2022, 5(4), 848-861; https://doi.org/10.3390/ceramics5040062 - 25 Oct 2022
Cited by 1 | Viewed by 1501
Abstract
The aim of this paper is to define and set up an experimental procedure, based on active thermography, for the characterization of coatings for industrial applications. This procedure is intended to be a fast and reliable method, alternative to the consolidated one described [...] Read more.
The aim of this paper is to define and set up an experimental procedure, based on active thermography, for the characterization of coatings for industrial applications. This procedure is intended to be a fast and reliable method, alternative to the consolidated one described in International Standards. In more detail, a classical active thermographic set up, and not a dedicated apparatus, was used for that aim, and data processing techniques referred to the analytical approach described in Standards. The active thermography procedure provided the measurement of the surface temperature of specimens undergoing a thermal excitation, applied by means of a laser pulse (Pulsed Technique). Temperature data processing, according to and adapting the Standard procedures, allowed to obtain thermal conductivity and diffusivity information. In particular, two coating processes (Atmospheric and Suspension Plasma Spray) applied to the same base material, Inconel 601, and the same coating material were investigated. These results were compared in terms of thermal properties variation with respect to base and coated materials, and in terms of different coating processes (APS and SPS). Obtained results were also compared to those available in literature. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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9 pages, 26580 KiB  
Article
Electron-Beam Deposition of Metal and Ceramic-Based Composite Coatings in the Fore-Vacuum Pressure Range
by A. V. Tyunkov, A. S. Klimov, K. P. Savkin, Y. G. Yushkov and D. B. Zolotukhin
Ceramics 2022, 5(4), 789-797; https://doi.org/10.3390/ceramics5040057 - 17 Oct 2022
Cited by 1 | Viewed by 1556
Abstract
We present the experimental results on the fabrication of metal-ceramic coatings by electron-beam evaporation of alumina ceramic and copper powder composites with different fractions of the components (with Cu powder fraction from 0.1 to 20%) pre-sintered by an electron beam. The mass-to-charge composition [...] Read more.
We present the experimental results on the fabrication of metal-ceramic coatings by electron-beam evaporation of alumina ceramic and copper powder composites with different fractions of the components (with Cu powder fraction from 0.1 to 20%) pre-sintered by an electron beam. The mass-to-charge composition of the multi-component plasma, generated in the electron beam transport region, was measured, demonstrating that the fraction of target ions in plasma grows with the electron beam power density. The morphology and electrical conductivity of fabricated coatings were investigated; it was found that the increase in Cu fraction in the deposited coating from 0 to 20% decreases both the volumetric and surface resistance of the coatings in around 8 orders of magnitude, thereby being a convenient tool to control the coating properties. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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13 pages, 3154 KiB  
Article
Electron-Beam Sintering of Al2O3-Cr-Based Composites Using a Forevacuum Electron Source
by Aleksandr Klimov, Ilya Bakeev, Anna Dolgova, Efim Oks, Van Tu Tran and Aleksey Zenin
Ceramics 2022, 5(4), 748-760; https://doi.org/10.3390/ceramics5040054 - 14 Oct 2022
Viewed by 1309
Abstract
We describe our studies of the influence of Cr content in an Al2O3-Cr composite on its thermal and electrical conductivity properties during and after electron-beam sintering in the forevacuum range of pressure. Sintering was carried out using a plasma-cathode [...] Read more.
We describe our studies of the influence of Cr content in an Al2O3-Cr composite on its thermal and electrical conductivity properties during and after electron-beam sintering in the forevacuum range of pressure. Sintering was carried out using a plasma-cathode forevacuum-pressure electron source of an original design, capable of processing non-conducting materials directly. It is shown that the chromium content affects the efficiency of the beam power transfer to the irradiated composite. The efficiency decreases with increasing chromium content. Measurement of the composite’s coefficient of thermal conductivity, in the temperature range 50–400 °C, shows that it varies almost linearly from 25 W/(m∙K) to 68 W/(m∙K) as the Cr content in the composite increases from 25% to 75% wt. The electrical conductivity properties after sintering exhibit a non-linear behavior. The conduction activation energy Ea, measured via the dependence of the current through composites of different compositions, is slightly lower than the Al2O3 band-gap. The addition of metallic Cr results in a disproportionate decrease in Ea, almost by an order of magnitude, from 6.9 eV to 0.68 eV. By varying the chromium content, it is possible to form a material with thermal and electrical conductivities controllable over a wide range. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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15 pages, 2623 KiB  
Article
Electron-Beam Synthesis and Modification and Properties of Boron Coatings on Alloy Surfaces
by Yury Yushkov, Efim Oks, Andrey Kazakov, Andrey Tyunkov and Denis Zolotukhin
Ceramics 2022, 5(4), 706-720; https://doi.org/10.3390/ceramics5040051 - 10 Oct 2022
Cited by 4 | Viewed by 1927
Abstract
In this study, fore-vacuum plasma electron beam sources were used to deposit a few micron-thick boron coatings on A284 and ZrNb1 alloys and modify their surfaces. The coating deposition rate with a continuous 1 kW electron beam that evaporated the boron target at [...] Read more.
In this study, fore-vacuum plasma electron beam sources were used to deposit a few micron-thick boron coatings on A284 and ZrNb1 alloys and modify their surfaces. The coating deposition rate with a continuous 1 kW electron beam that evaporated the boron target at a distance of 10 cm was 0.5 µm/min, and the boron coating density was 2.2 g/cm3. Based on the comparison of data on the mass-to-charge composition, beam plasma density, and coating parameters, the contribution of the plasma phase of the evaporated material to the growth of coatings was greater than that of the vapor phase. Using the scanning electron and atomic force microscopy techniques, surface modification by repeated electron beam pulses with electron energies of 8 and 6 keV and a beam power per pulse of 2 J/cm2 and 2.25 J/cm2, respectively, transformed a relatively smooth coating surface into a hilly structure. Based on a structural phase analysis of coatings using synchrotron radiation, it was concluded that the formation of the hilly coating structure was due to surface melting under the repeated action of electron beam pulses. The microhardness, adhesion, and wear resistance of coatings were measured, and their corrosion tests are presented herein. The pure boron coatings obtained and studied are expected to be of use in various applications. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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13 pages, 4325 KiB  
Article
CaO-SiO2-B2O3 Glass as a Sealant for Solid Oxide Fuel Cells
by Andrey O. Zhigachev, Ekaterina A. Agarkova, Danila V. Matveev and Sergey I. Bredikhin
Ceramics 2022, 5(4), 642-654; https://doi.org/10.3390/ceramics5040047 - 21 Sep 2022
Viewed by 2152
Abstract
Solid oxide fuel cells (SOFCs) are promising devices for electrical power generation from hydrogen or hydrocarbon fuels. The paper reports our study of CaO-SiO2-B2O3 material with composition 36 mol.% SiO2, 26 mol.% B2O3 [...] Read more.
Solid oxide fuel cells (SOFCs) are promising devices for electrical power generation from hydrogen or hydrocarbon fuels. The paper reports our study of CaO-SiO2-B2O3 material with composition 36 mol.% SiO2, 26 mol.% B2O3, and 38 mol.% CaO as a high-temperature sealant for SOFCs with an operating temperature of 850 °C. The material was studied as an alternative to presently existing commercial glass and glass-ceramics sealants for SOFCs with operating temperature of 850 °C. Many of these sealants have limited adhesion to the surface of Crofer 22APU steel, commonly used in these SOFCs. The present study included X-ray diffraction, dilatometric, thermal, and microstructural analysis The study has shown that the softening point of the CaO-SiO2-B2O3 glass is around 900 °C, allowing sealing of the SOFCs with this glass at convenient temperature of 925 °C. The CaO-SiO2-B2O3 glass sealant has shown excellent adhesion to the surface of Crofer 22APU steel; SEM images demonstrated evidences of chemical reaction and formation of strong interface on sealant–steel contact surface. Furthermore, the glass has shown a coefficient of thermal expansion about 8.4 × 10−6 1/K after sealing, making it thermomechanically compatible with the existing SOFC materials. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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Review

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29 pages, 5658 KiB  
Review
State-of-the-Art Developments in Advanced Hard Ceramic Coatings Using PVD Techniques for High-Temperature Tribological Applications
by Dinesh Kumar Devarajan, Baskaran Rangasamy and Kamalan Kirubaharan Amirtharaj Mosas
Ceramics 2023, 6(1), 301-329; https://doi.org/10.3390/ceramics6010019 - 21 Jan 2023
Cited by 8 | Viewed by 2863
Abstract
Hard and wear-resistant coatings created utilizing physical vapor deposition (PVD) techniques are extensively used in extreme tribological applications. The friction and wear behavior of coatings vary significantly with temperature, indicating that advanced coating concepts are essential for prolonged load-bearing applications. Many coating concepts [...] Read more.
Hard and wear-resistant coatings created utilizing physical vapor deposition (PVD) techniques are extensively used in extreme tribological applications. The friction and wear behavior of coatings vary significantly with temperature, indicating that advanced coating concepts are essential for prolonged load-bearing applications. Many coating concepts have recently been explored in this area, including multicomponent, multilayer, gradient coatings; high entropy alloy (HEA) nitride; and functionally modified coatings. In this review, we highlighted the most significant findings from ongoing research to comprehend crucial coating properties and design aspects. To obtain enhanced tribological properties, the microstructure, composition, residual stress, hardness, and HT oxidation resistance are tuned through doping or addition of appropriate materials at an optimized level into the primary coatings. Such improvements are achieved by optimizing PVD process parameters such as input power, partial pressure, reactive gas flow rates, substrate bias, and temperature. The incorporation of ideal amounts of Si, Cr, Mo, W, Ag, and Cu into ternary and quaternary coatings, as well as unique multilayer designs, considerably increases the tribological performance of the coatings. Recent discoveries show that not only mechanical hardness and fracture toughness govern wear resistance, but also that oxidation at HT plays a significant role in the lubrication or wear failure of coatings. The tribo-induced metal oxides and/or Magnéli phases concentrated in the tribolayer are the key governing factors of friction and wear behavior at high temperatures. This review includes detailed insights into the advancements in wear resistance as well as various failure mechanisms associated with temperature changes. Full article
(This article belongs to the Special Issue Ceramic Coatings for High-Temperature Applications)
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