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A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Laser Coatings".

Deadline for manuscript submissions: closed (31 January 2025) | Viewed by 16739

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Dr. Oana Catalina Mocioiu

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Institute of Physical Chemistry "Ilie Murgulescu", 202 Splaiul Independenţei, 060021 Bucharest, Romania
Interests: SiO2-ZnO materials; oxide systems obtained by sol-gel; ZnO-SnO-based ceramics; hybrid nanocomposites; oxide compounds and materials science
Special Issues, Collections and Topics in MDPI journals

Dr. Ana-Maria Mocioiu

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National Research & Development Institute for Non-ferrous and Rare Metals-INCDMR- IMNR, 102 Biruinţei Blvd, Pantelimon, 077145 Ilfov, Romania
Interests: advanced nanomaterials; functionalized textiles; coatings for special properties (corrosion resistance, antibacterial, self cleaning, etc); thin films; alloys with special properties and so on
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

We are launching this new Special Issue of Coatings that will collect original research articles and review papers. The theme of this Special Issue focuses on obtaining/characterizing/applying coatings that include thermal treatment (cooling or heating) or a laser-assisted process.

In the volume are targeted studies of materials for coatings that in the obtaining stage use heat/cooling treatment or laser-assisted processes or are obtained directly by combustion.

Materials for coatings characterized in terms of heating or cooling behavior, e.g., Differential Thermal Analysis, Differential Scanning Calorimetry, Thermal Mechanic Analysis, measurements in the cryogenic environment are included. Materials characterized by Dynamic Light Scattering or materials for applications as lasers (glasses or oxides) can be published.

New manufacturing technologies covering different materials, such as 3D Printing, Selective Laser Sintering, Rapid Prototyping, Rapid Thermal Annealing, Chemical Vapor Deposition, E-Gun Technology, RF Sputtering are welcome.

Dr. Oana Catalina Mocioiu
Dr. Ana-Maria Mocioiu
Guest Editors

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.

Keywords

thermal treatment
laser process
coatings
advanced materials

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Published Papers (10 papers)

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Research

9 pages, 2573 KiB

Open AccessArticle

Influence of Laser Remelting on Creep Resistance in Ti-6Al-4V Alloy with Thermal Barrier Coating

by Filipe Estevão de Freitas, Roberta Aguiar Luna da Silva, Renata Jesuina Takahashi, Adriano Gonçalves dos Reis, Aline Gonçalves Capella and Danieli Aparecida Pereira Reis

Coatings 2025, 15(2), 220; https://doi.org/10.3390/coatings15020220 - 12 Feb 2025

Viewed by 586

Abstract

Ti-6Al-4V alloys with a thermal barrier coating (TBC) have been applied in aeronautical components as turbine blades to provide oxidation resistance and thermal protection, enabling higher operating temperatures and extending component lifespan. Research into TBCs with laser surface modification has investigated improving their mechanical and thermal properties. This study assessed the creep behavior of Ti-6Al-4V alloy with a TBC, where the coating was applied via CO₂ laser-remelted plasma spraying. Creep tests were conducted at a constant temperature and a load ranging from 500 to 700 °C at 125 MPa. The microstructure and fractography of the specimens were also investigated. The investigation also included microstructural and fractographic analyses of the specimens. The results indicate that the laser-remelted TBC provided effective thermal protection and increased oxidation resistance, with the stationary creep rate at 600 °C reduced by 50% and the creep rupture life extended by 20%. Observations revealed typical ductile fractures characterized by equiaxed dimples and a homogeneous microstructure with an equiaxed dual-phase (α+β) structure near the fracture zone. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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21 pages, 17862 KiB

Open AccessArticle

The Laser Processing of the Stainless-Steel Surface Layer of a Heat Exchanger Membrane in Order to Enhance Its Heat Transfer Coefficient

by Ewa Dorota Kozłowska, Marek Szkodo, Tomasz Muszyński and Paulina Adamska

Coatings 2025, 15(1), 72; https://doi.org/10.3390/coatings15010072 - 10 Jan 2025

Viewed by 807

Abstract

Research on temperature regulation is essential for ensuring thermal comfort and optimizing machine performance. Effective cooling systems are critical in industrial processes and everyday electronic devices in order to prevent overheating. Laser-modified heat exchangers can enhance heat dissipation without increasing weight, addressing the need for energy-efficient solutions in the market. The main aim of this experimental research was to establish an efficient method for altering the surface layer of AISI 316L stainless steel with laser pulses and to determine the effectiveness of the laser alterations to the surface layer in the context of intensifying the convective heat transfer. A series of laser-texturing processes was performed on the surface layer of AISI 316L steel using a Nd: YAG pulse laser. Selected samples were subjected to a series of measurements using a recuperator-type heat exchanger. Based on the measurements’ results, the heat transfer coefficients, α, obtained from the modified surfaces were determined. The results were compared with other data from the existing literature and those obtained from unmodified reference samples. The intensification of the convective heat transfer was achieved for 43% of the modifications conducted with a pulsed laser. The highest observed average increase in the heat transfer coefficient, α, was 16.53%. However, the effective intensification of the convective heat transfer, in some cases, was only observed for a certain range of temperatures or flow dynamics parameters. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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24 pages, 26404 KiB

Open AccessArticle

Effects of Different Surface Treatment Methods on Laser Welding of Aluminum Alloy and Glass

by Changjun Chen, Lei Li, Min Zhang and Wei Zhang

Coatings 2024, 14(10), 1318; https://doi.org/10.3390/coatings14101318 - 15 Oct 2024

Cited by 1 | Viewed by 1509

Abstract

Hermetic glass-to-metal sealing (GMTS) technology combines metal and glass and can be used to construct vacuum tubes; electric discharge tubes; semiconductor diodes; reed switches; and pressure-tight glass-to-metal windows, optical windows, and lenses in electronics or electronic systems. The hermetic and mechanically strong seals engineered using GTMS are highly reliable, making them suitable for deployment in harsh environments and for applications requiring high performance. However, it has always been challenging to precisely and robustly join glass and metal due to the significant disparities in their properties. In this study, the laser transmission welding of borosilicate glass and aluminum alloy using a pulsed Nd:YAG laser to achieve hermetic glass–metal seals was experimentally investigated. This research focused on various processing parameters and the influence of surface conditions on bonding quality. Three different types of surfaces—a polished surface, a surface subjected to preoxidation, and a laser-modified surface—were compared. To evaluate the weld strength, shear-tensile separation forces were measured. The analysis of fracture and separation encompassed detailed examinations of the weld morphology, microstructure, and elemental composition. The results revealed that increasing the laser welding energy initially enhanced the weld strength until a saturation point was reached. Among the three different surface treatments tested, the laser surface modification of aluminum alloy yielded the highest weld strength. The maximum achieved bond force exceeded 35.38 N, demonstrating the feasibility of using cost-effective pulsed laser welding for glass-to-metal sealing. The results were significantly better than those from previous research in which aluminum alloy surfaces were pretreated using microarc oxidation. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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17 pages, 3996 KiB

Open AccessArticle

Study of Ceramic Hollow Buoyant Balls Prepared Based on Slip Mold Casting and Brazing Process

by Yu Lei, Jian Zhou, Guizhen Liu, Lin Wang and Zhongjun Ding

Coatings 2024, 14(6), 767; https://doi.org/10.3390/coatings14060767 - 17 Jun 2024

Viewed by 1534

Abstract

In the domain of deep-sea buoyancy material applications, hollow ceramic spheres, known for their high strength and low mass-to-drainage ratio, contribute to increased buoyancy and payload capacity enhancement for deep submersibles, constituting buoyancy materials of exceptional overall performance. This study entails the brazing of two ceramic hemispherical shells, obtained through slurry molding, to form a ceramic float. This process, which integrates slurry molding and ceramic brazing, facilitates buoyancy provision. Further refinement involves welding a ceramic connector onto the ceramic shell, incorporating a top opening to create a ceramic float equipped with an observation window seat. The ceramic float maintains uniform wall thickness, while the observation window facilitates external environmental observation in deep-sea research. Two pressure-resistant spherical shells, produced using this process, underwent testing, revealing the wall thickness of the prepared alumina ceramic hollow spheres to be 1.00 mm, with a mass-to-drainage ratio of 0.47 g/cm³ and a buoyancy coefficient of 53%. The resultant ceramic hollow floating ball can withstand hydrostatic pressure of 120 MPa, while the pressure-resistant ball shell with an observation window seat can endure hydrostatic pressure of 100 MPa, ensuring safe operation at depths of 5000–6000 m. This process provides a production method for subsequent large-scale ceramic float manufacturing for the transportation of objects or personnel. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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17 pages, 3472 KiB

Open AccessArticle

Determination of Fe₃O₄ Content and Total Nonhydraulic Minerals in Steel Slag

by Xinkai Hou, Jiaoyang Sun, Xiangfeng Wang, Xiaoqi Fan and Ying Wang

Coatings 2024, 14(5), 593; https://doi.org/10.3390/coatings14050593 - 9 May 2024

Viewed by 1284

Abstract

The nonhydraulic minerals (Fe₃O₄, RO phase, Fe) in slag are important indicators for evaluating the pozzolanic activity and detecting the quality of the slag activation processing technology. Fe₃O₄ is an important characteristic mineral among the nonhydraulic minerals. In order to accurately assess the pozzolanic activity of steel slag powder and to monitor the quality of the activation process of steel slag powder for separate nonhydraulic minerals, it is imperative to precisely determine the nonhydraulic mineral content within the steel slag. Further refinement and enhancement are required for both the HNO₃ dissolution method used in determining Fe₃O₄ content in steel slag, as well as for the EDTA-DEA-TEA (ethylenediamine tetraacetate sodium-diethylamine-triethanolamine) dissolution method employed in determining total nonhydraulic minerals, due to potential deviations caused by challenging impurity separations. The results show that the content of Fe₃O₄ is determined by 10%HNO₃-20%NaOH-chemical analysis method, which solves the problem that the impurities of refractory materials (quartz, corundum, mullite) and amorphous phase affects the content determination in HNO₃ dissolution method. The total amount of nonhydraulic minerals (Fe₃O₄, RO phase, Fe) was determined by the EDTA-NaOH-TEA dissolution method, which solved the problem that the incomplete dissolution of C₂F in the EDTA-DEA-TEA dissolution method affected the content determination. The maximum error between the content determination value and the theoretical calculation value of the two methods is less than 0.50%. The improved Fe₃O₄ and total nonhydraulic mineral quantification methods are feasible and reliable. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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12 pages, 25548 KiB

Open AccessArticle

Hydrophobic and Transparent Tantalum Pentoxide-Based Coatings for Photovoltaic (PV) Solar Panels

by Oana Cătălina Mocioiu, Irina Atkinson, Ludmila Aricov, Veronica Bratan, Ana-Maria Mocioiu, Ioan Albert Tudor and Diana Irinel Băilă

Coatings 2024, 14(3), 273; https://doi.org/10.3390/coatings14030273 - 23 Feb 2024

Viewed by 1686

Abstract

Photovoltaic (PV) solar panels suffer from efficiency losses due to the accumulation of dust on their surface during operation, as well as the loss of transparency in the top glass. The efficiency can be increased when hydrophobic films are deposited on the top glass of the solar cells. The top glass of solar cells must have three characteristics: high transmittance in the 380–750 nm range, a band gap greater than 3.2 eV and a refractive index higher than 1.23. So, the films require the same characteristics. This work presents an increase in the contact angle (related to an increase in the hydrophobic character) when Ta₂O₅ is partially substituted with ZnO. The studied films, physically deposited on glass by e-gun technology, present a non-crystalline state in the form of the X-ray patterns shown. The films have a transmission of 75%–80% in the visible range. The morphology and roughness of the coatings were evaluated by atomic force microscopy. All films show the values of the Millipore water contact angle higher than 91 degrees, leading to the acquisition of hydrophobic properties on the surface. In comparison, the substrate is hydrophilic, with an average contact angle of 53.81 ± 2.16. The hydrophobic properties and self-cleaning ability make the films recommendable for application. The band gap of the coatings was calculated with the Tauc method, and they have values of 4.5–4.6 eV. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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18 pages, 39004 KiB

Open AccessArticle

Influence of Thermo-Mechanical Process and Nb-V Microalloying on Microstructure and Mechanical Properties of Fe–Mn–Al–C Austenitic Steel

by Ting Zhao, Xiaohong Hao, Yuefeng Wang, Chen Chen and Tiansheng Wang

Coatings 2023, 13(9), 1513; https://doi.org/10.3390/coatings13091513 - 27 Aug 2023

Cited by 2 | Viewed by 1447

Abstract

In present study, a novel Nb-V microalloyed Fe–Mn–Al–C steel and a non-microalloyed Fe–Mn–Al–C austenitic steel were treated with different thermo-mechanical processes. The microstructure of the test steels was observed by scanning electron microscope, transmission electron microscope, electron probe micro-analyzer, and X-ray diffractometer. A tensile test was conducted to estimate the mechanical properties of the test steels. Results show that the equiaxed austenitic grains are obtained in both test steels, while hot rolling reduces the grain size significantly. The grain size of the Fe–Mn–Al–C steel decreases by 40%–55% after the addition of Nb-V due to the precipitation of nanoscale (Nb,V)C particles within the austenite matrix. Compared with the solid solution treated specimens, the strength of the hot-rolled or aged specimens is improved. Meanwhile, the strength of the Fe–Mn–Al–C steel with Nb-V microalloying is also increased by 55 MPa due to the precipitation strengthening and fine grain strengthening, while the elongation is decreased. The Nb-V microalloyed Fe–Mn–Al–C steel, after hot rolling + aging treatment, obtains the maximum strength, with the yield and tensile strength of 669 MPa and 1001 MPa, respectively. The strengthening mechanisms that contribute significantly to the yield strength are solid solution strengthening and dislocation strengthening. They are 185 MPa and 211 MPa, respectively, for the Nb-V microalloyed Fe–Mn–Al–C steel at hot rolling + aging conditions. Meanwhile, the segregation of carbon atoms after aging treatment also improves the yield strength significantly. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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12 pages, 3938 KiB

Open AccessArticle

Effects of Er,Cr: YSGG Laser Application in De-Bonding of Different Ceramic Veneer Materials (In Vitro Study)

by Bassam Karem Amin

Coatings 2023, 13(8), 1352; https://doi.org/10.3390/coatings13081352 - 2 Aug 2023

Cited by 1 | Viewed by 2127

Abstract

Background: Ceramic restorations are widely used nowadays as the esthetic demand has increased in the worldwide population, and lithium disilicate and feldspathic porcelain materials are the most widely used veneer materials. The traditional removal procedure for veneers was recently replaced with the use of laser technology to debond the veneers so that the de-bonded veneers can be preserved and re-used. Aim: Up to now, there have been few studies regarding using lasers to remove ceramic laminate; thus, it is clear why this research topic is important for examining the efficiency of lasers in the use of de-bonding for different ceramic laminates with varying compositions and materials. Materials and Methods: This study employed forty-five normal human maxillary first premolars with comparable proportions. The forty-five teeth were initially split into three groups of fifteen teeth, and the teeth were chosen at random. Each group fused pairs of various ceramic materials. A total of fifteen teeth in the first group underwent feldspathic porcelain restorations. The second group contained fifteen restorations made of lithium disilicate glass-ceramic CAD-CAM. In the third group, fifteen teeth were restored using glass-ceramic that had a lithium disilicate glass-ceramic ingot. The RelyX Veneer A1 shade, available from 3M EPSE in the United States, was used to bond all the samples. The specimens were then submerged for approximately 24 h in distilled water at 37 degrees Celsius in order to simulate the conditions in an oral cavity. An Er,Cr: YSGG laser (Waterlase, iPlus, Biolase, from USA) was used with a turbo headpiece and an MX7 sapphire tip for irradiation. Results: The time needed for the ceramic disc to debond was calculated using a digital stopwatch. The average removal times for the feldspathic porcelain, lithium disilicate glass-ceramic ingot, and lithium disilicate glass-ceramic CAD-CAM were 10.067 ± 1.668 s, 5.200 ± 1.146 s, and 5.133 ± 1.125 s, while the removal times ranged from 8–12 s, 4–7 s, and 4–7 s, respectively. Compared to the other ceramic materials, de-bonding the feldspathic porcelain took longer. Conclusions: According to this study, the Er,Cr: YSGG laser application using the same study parameters made it simpler to de-bond lithium disilicate and feldspathic porcelain. Lithium disilicate, as opposed to feldspathic porcelain, transmits laser light more effectively; hence, the results varied depending on the materials, and the debonding occurred primarily at the veneer–cement interface. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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10 pages, 3412 KiB

Open AccessArticle

Comparison of RF and High Impulse Magnetron Sputtered Gallium-Doped Zinc Oxide Thin Films

by Justin Ryan Phelps, Ashwin Kumar Saikumar, Reza Abdolvand and Kalpathy B. Sundaram

Coatings 2023, 13(1), 71; https://doi.org/10.3390/coatings13010071 - 31 Dec 2022

Cited by 2 | Viewed by 2156

Abstract

For the first time in the literature, the material properties of gallium-doped zinc oxide, grown from a high impulse magnetron sputtering system (HiPIMS), are reported. These material properties are compared to those of a typical radio frequency (RF) sputtering deposition. The films were grown without thermal assistance and were compared across multiple average deposition powers. The films’ resistivity, crystallinity, absorption coefficient, band gap, and refractive index were measured for each of the samples. It was observed that very similar results could be obtained between the HiPIMS and RF sputtering processes under the same average power conditions. It was found that the RF depositions demonstrated a slightly higher band gap and deposition rate as well as lower resistivity and optical absorption coefficient. Band gaps and grain size were found to increase with the power of the deposition for both HiPIMS and RF. These values ranged between 3.45 eV and 3.79 eV and 9 nm and 23 nm in this study, respectively. The absorption coefficient and resistivity were both found to decline with increasing power in both methods but reached minimums of 2800 cm⁻¹ and 0.94 mOhm-cm, respectively, when sputtered using an RF power supply. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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15 pages, 5239 KiB

Open AccessArticle

Laser Curing of Digitally Printed Polymer–Silver Composite Conductive Tracks on Polycarbonate Substrates

by Jonas Mertin, Tamila Rozibakieva, Christian Vedder and Jochen Stollenwerk

Coatings 2023, 13(1), 10; https://doi.org/10.3390/coatings13010010 - 21 Dec 2022

Viewed by 2033

Abstract

In this article, we present an approach to fabricate conductive tracks on polymer substrates. Here, a digital printing process is used together with subsequent processing by a laser. For this purpose, a silver flake-based composite is printed onto a polycarbonate substrate using a jet-dispensing process. The printed tracks are then cured using a pyrometer-controlled laser beam source. The fabricated samples are analyzed for electrical resistivity and the cross-sectional area of the conductive tracks and compared to conventionally oven-cured samples. Four-point measurements and an optical measurement method are used for this purpose. Based on the resulting resistance, two different process regimes can be observed for the laser curing process. By using a laser instead of an oven for post-treatment, the achieved resistance of the conductive tracks can be reduced by a factor of 2. Moreover, the tracks produced in this way are more reproducible in terms of the resistance that can be achieved. Full article

(This article belongs to the Special Issue Laser-Assisted Processes and Thermal Treatments of Materials)

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