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Surface Treatments and Coating of Metallic Materials (2nd Edition)
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Surface Treatments and Coating of Metallic Materials (2nd Edition)

A special issue of Metals (ISSN 2075-4701). This special issue belongs to the section "Corrosion and Protection".

Deadline for manuscript submissions: 31 July 2026 | Viewed by 4147

Special Issue Editor

Dr. Luca Pezzato

E-Mail Website
Guest Editor
Institute of Condensed Matter Chemistry and Energy Technologies, National Research Council of Italy, 35127 Padova, Italy
Interests: metallurgy; corrosion; coatings
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Surface treatments and coating technologies are of extremely great interest in the metallurgical sector because they permit the functionalization of the metal surface, thus modifying the part of the metal that interacts with the environment and permitting the obtaining of particular properties that cannot be obtained with only the bulk material. There are a wide range of properties that can be modified with surface treatments; the most common treatments are performed in order to improve the wear and corrosion properties of metals, but treatments are also often performed in order to provide some particular functionality to the metal surfaces. The classification of surface treatments is generally performed on the basis of the thickness of the coating (thick or thin coating) or on the basis of the type of deposition (deposition from the liquid, solid, or vapor phase). The type of coating generally depends both on the type of application of the final product and on the composition of the metallic substrate.

The purpose of this Special Issue, for which a second edition is now being published thanks to the success of the first one, is to publish studies that deal with surface treatments of metallic materials. These may include, but are not limited to, the following:

  • Coatings deposited from the vapor phase (PVD, CVD, and PA-CVD);
  • Coatings deposited from the liquid phase: anodizing, plasma electrolytic oxidation, other conversion treatments, electroplating of metallic coatings, hot-dip galvanizing, or electroless deposition;
  • Coatings deposited from the solid phase: thermal spray coating, laser cladding, or welded coatings;

We invite you to submit both original contributions and review works on these topics, with papers that deal with both production methods and the characterization of the coatings produced on different metal substrates being particularly encouraged. 

Dr. Luca Pezzato
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 250 words) can be sent to the Editorial Office for assessment.

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. Metals 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

  • coatings
  • surface treatments
  • corrosion resistance
  • wear resistance
  • PVD
  • CVD
  • PEO
  • anodizing
  • electroplating
  • hot-dip galvanizing
  • thermal spray
  • laser cladding

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Further information on MDPI's Special Issue policies can be found here.

Published Papers (7 papers)

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Research

Jump to: Review

19 pages, 6340 KB  
Article
Validation of a Surface Chemical Attack Process on Precision Metal Spheres for Use in Non-Contact Metrology
by Eduardo Cuesta, Víctor M. Meana, Braulio J. Álvarez, José Ablanedo and Sara Giganto
Metals 2026, 16(4), 381; https://doi.org/10.3390/met16040381 - 30 Mar 2026
Viewed by 456
Abstract
This work aims to find a chemical process that modifies the surface finish of precision metal spheres to enable their use as reference elements in optical metrology. The chemical process should not substantially alter the original quality or dimensional accuracy, but it should [...] Read more.
This work aims to find a chemical process that modifies the surface finish of precision metal spheres to enable their use as reference elements in optical metrology. The chemical process should not substantially alter the original quality or dimensional accuracy, but it should give the spheres a matte finish, eliminating reflections. The spheres used are AISI 316L stainless steel bearing spheres, which are of low cost, high availability and great dimensional accuracy, making them suitable as reference elements if their high gloss is removed. Two procedures are tested in the research. On the one hand, different passivation acids are tested, and on the other, a chemical attack with a much more aggressive acid, aqua regia (hydrochloric acid, HCl, and nitric acid, HNO3, in a 1:3 ratio). Tests showed that none of the passivation methods sufficiently eliminated glare and reflections. However, chemical etching by immersion in aqua regia did produce a matte and homogeneous surface finish, reducing reflectivity and promoting the diffusion of incident light without loss of precision. The paper presents the tests to find the optimal exposure time to aqua regia as well as the influence of chemical etching from a dimensional and geometrical point of view, both in contact and laser sensor optical measurement. The research has considered a representative series of the chemical attack procedure to validate the repeatability of the method. Finally, it has been verified that the method is repeatable and that improvements (close to 45%) in the metrological accuracy of the laser sensor measurements are achieved when using spheres treated with aqua regia compared to original spheres. In conclusion, it has been demonstrated that the chemical attack with aqua regia is not only a valid method for generating matte surfaces suitable for optical metrology, but a process that can also be implemented at low cost and with high reproducibility. Full article
(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials (2nd Edition))
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24 pages, 8730 KB  
Article
Research on the Mechanism of Fabricating Hierarchical Microstructured Hydrophobic Surfaces via Laser Ablation Imprinting
by Genyi Li, Pin Li, Rui Zhang, Haoran Sun, Zheng Shi and Zongbao Shen
Metals 2026, 16(3), 349; https://doi.org/10.3390/met16030349 - 20 Mar 2026
Viewed by 299
Abstract
This study aims to reveal the mechanism of a novel method for fabricating hierarchical microstructured hydrophobic surfaces. Specifically, plasma shock waves induced by laser ablation are applied to the workpiece to replicate the microstructures on the mold surface, thus obtaining primary microstructures. Meanwhile, [...] Read more.
This study aims to reveal the mechanism of a novel method for fabricating hierarchical microstructured hydrophobic surfaces. Specifically, plasma shock waves induced by laser ablation are applied to the workpiece to replicate the microstructures on the mold surface, thus obtaining primary microstructures. Meanwhile, the material splashing effect induced by laser ablation is utilized to form secondary microstructures on the basis of the primary microstructures. Subsequently, fluorination treatment and aging treatment are adopted to alter the chemical composition of the hierarchical microstructures on the workpiece surface, thereby reducing the surface energy and enhancing hydrophobicity. In addition, this study investigates the effects of a different number of laser shocks, laser fluence and mold periods on the forming results. Under a laser fluence of 28.97 J/cm2, within the range of one to five laser shocks, the forming effect of the aluminum foil workpiece improves with the increase in the number of laser shocks. When the number of laser shocks is set to 3, within the laser fluence range of 19.1–76.39 J/cm2, the forming result of the aluminum foil workpiece is enhanced as the laser fluence increases. The larger the mold period, the better the forming effect of the workpiece. An analysis of aging treatment and fluorination treatment reveals their impacts on the workpiece through assessments of wettability, surface chemical composition, and surface morphology. The findings reveal that both aging and fluorination treatments significantly enhance the contact angle of the aluminum foil workpiece, all while preserving its original surface structure. The main changes occur in terms of element content and chemical composition, and a large number of non-polar groups are generated on the workpiece surface after the modification treatments. Full article
(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials (2nd Edition))
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17 pages, 4709 KB  
Article
Experimental Investigations of Oxidation Formation During Pulsed Laser Surface Structuring on Stainless Steel AISI 304
by Tuğrul Özel and Faik Derya Ince
Metals 2026, 16(2), 224; https://doi.org/10.3390/met16020224 - 15 Feb 2026
Viewed by 499
Abstract
Laser surface texturing (LST) structures or laser-induced periodic surface structures (LIPSS) are typically created using laser pulses with durations ranging from femtoseconds to nanoseconds. However, nanosecond pulsed lasers, as cost-effective and more productive alternatives, can also be used to generate LST structures on [...] Read more.
Laser surface texturing (LST) structures or laser-induced periodic surface structures (LIPSS) are typically created using laser pulses with durations ranging from femtoseconds to nanoseconds. However, nanosecond pulsed lasers, as cost-effective and more productive alternatives, can also be used to generate LST structures on stainless steel (SS) surfaces, making these structures more suitable for industrial applications. In this study, pulsed laser processing is employed to create LST structures on SS (AISI 304), with varying pulse and accumulated fluences, effective pulse counts, and scan parameters, such as pulse-to-pulse distance (pitch) and hatch spacing between scanning lines. A methodology for calculating oxidation density on processed AISI 304 surfaces is presented. Oxidation density, defined as the ratio of the oxidized area to the total processed area, is determined as a function of accumulated fluence, laser power, pulse-to-pulse distance, and hatch spacing. Optical images of the surfaces are analyzed, and oxidation regions are identified using machine learning techniques. The images are converted to grayscale, and machine learning algorithms are applied to classify the images into oxidation and non-oxidation regions based on pixel intensity values. This approach identifies the optimal threshold for separating the two regions by maximizing inter-class variance. Experimental modeling using response surface methodology is applied to experimentally generated data. Optimization algorithms are then employed to determine the process parameters that maximize pulsed laser irradiation performance while minimizing surface oxidation and processing time. This paper also presents a novel method for characterizing oxidation density using image segmentation and machine learning. The results provide a comprehensive understanding of the process and offer optimized models, contributing valuable insights for practical applications. Full article
(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials (2nd Edition))
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19 pages, 17087 KB  
Article
Microstructural and Wear Characterisation of Aluminium 7075-Based Metal Matrix Composites Reinforced with High-Entropy Alloy Particles and Manufactured via Friction Stir Processing
by Leire Garcia-Sesma, Javier Vivas, Iban Quintana and Egoitz Aldanondo
Metals 2026, 16(2), 132; https://doi.org/10.3390/met16020132 - 23 Jan 2026
Viewed by 409
Abstract
This study investigates the microstructural evolution and wear behaviour of aluminium 7075-based metal matrix composites (MMCs) reinforced with high-entropy alloy (HEA) particles and fabricated via friction stir processing (FSP). A detailed characterisation of the grain refinement in the 7075 matrix was conducted, revealing [...] Read more.
This study investigates the microstructural evolution and wear behaviour of aluminium 7075-based metal matrix composites (MMCs) reinforced with high-entropy alloy (HEA) particles and fabricated via friction stir processing (FSP). A detailed characterisation of the grain refinement in the 7075 matrix was conducted, revealing significant dynamic recrystallization and grain size reduction induced by the severe plastic deformation inherent to FSP. The interaction between the matrix and HEA particles was analysed, showing strong interfacial bonding, which was further influenced by post-processing heat treatments. These microstructural modifications were correlated with the wear performance of the composites, demonstrating enhanced resistance due to the synergistic effect of precipitates and particle reinforcement. The findings highlight the potential of FSP as a viable route for tailoring surface properties in advanced MMCs for demanding tribological applications. Full article
(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials (2nd Edition))
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18 pages, 5019 KB  
Article
A High-Solid-Content and Low-Surface-Treatment Epoxy-Polysiloxane Ceramic Metal Coating for Metal Anti-Corrosion in Harsh Environments
by Xiufen Liao, Liang Fan, Qiumei Jiang, Maomi Zhao, Songqiang Huang, Junxiang Lai, Congtao Sun and Baorong Hou
Metals 2026, 16(1), 123; https://doi.org/10.3390/met16010123 - 21 Jan 2026
Viewed by 596
Abstract
Conventional anticorrosive coatings suffer from limitations of low solid content and rigorous surface pretreatment, posing environmental and cost challenges in field applications. In this study, a novel high-solid-content (>95%) epoxy-polysiloxane (Ep-PSA) ceramic metal coating was prepared that enables low-surface-treatment application. The originality lies [...] Read more.
Conventional anticorrosive coatings suffer from limitations of low solid content and rigorous surface pretreatment, posing environmental and cost challenges in field applications. In this study, a novel high-solid-content (>95%) epoxy-polysiloxane (Ep-PSA) ceramic metal coating was prepared that enables low-surface-treatment application. The originality lies in the synergistic combination of nano-sized ceramic powders, high-strength metallic powders, polysiloxane resin (PSA), and solvent-free epoxy resin (Ep), which polymerize through an organic–inorganic interpenetrating network to form a dense shielding layer. The as-prepared Ep-PSA coating system chemically bonds with indigenous metal substrate via Zn3(PO4)2 and resin functionalities during curing, forming a conversion layer that reduces surface preparation requirements. Differentiating from existing high-solid coatings, this approach achieves superior long-term barrier properties, evidenced by |Z|0.01Hz value of 9.64 × 108 Ω·cm2, after 6000 h salt spray exposure—four orders of magnitude higher than commercial 60% epoxy zinc-rich coatings (2.26 × 104 Ω·cm2, 3000 h salt spray exposure). The coating exhibits excellent adhesion (14.28 MPa) to standard sandblasted steel plates. This environmentally friendly, durable, and easily applicable composite coating demonstrates significant field application value for large-scale energy infrastructure. Full article
(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials (2nd Edition))
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21 pages, 11015 KB  
Article
Enhancement of the Wear Properties of Tool Steels Through Gas Nitriding and S-Phase Coatings
by Sebastian Fryska, Mateusz Wypych, Paweł Kochmański and Jolanta Baranowska
Metals 2026, 16(1), 9; https://doi.org/10.3390/met16010009 - 21 Dec 2025
Cited by 1 | Viewed by 805
Abstract
Tool steels are critical for high-load applications, e.g., forging and metal-forming, where they face thermal cracking, fatigue, erosion, and wear. This study evaluates the impact of gas nitriding and S-phase PVD coatings on the mechanical and tribological properties of four tool steels: 40CrMnNiMo8-6-4, [...] Read more.
Tool steels are critical for high-load applications, e.g., forging and metal-forming, where they face thermal cracking, fatigue, erosion, and wear. This study evaluates the impact of gas nitriding and S-phase PVD coatings on the mechanical and tribological properties of four tool steels: 40CrMnNiMo8-6-4, 60CrMoV18-5, X50CrMoV5-2, and X38CrMoV5-3. Samples were heat-treated (quenched and tempered at 600 °C), then gas-nitrided at 575 °C for 6 h with nitriding potentials (Kn) of 0.18, 0.79, or 2.18, or coated via reactive magnetron sputtering in Ar/N2 or Ar/N2/CH4 atmospheres at 200 °C or 400 °C. Characterization involved XRD, LOM, FE-SEM, GDOES, Vickers hardness (HV0.1), and ball-on-disk wear testing with Al2O3_ counter-samples. Gas nitriding produced nitrogen diffusion layers (80–200 μm thick) and compound layers (ε-Fe(2-3)N, γ’-Fe4N) at higher Kn, increasing hardness by 80–100% (up to 1100 HV0.1 for steel X38CrMoV5-3). S-phase coatings (1.6–3.6 μm thick) formed expanded austenite with varying N content, achieving comparable hardness (up to 1100 HV0.1) in high-N2 atmospheres, alongside substrate diffusion layers. Both types of treatment enhance load-bearing capacity, adhesion, and durability, offering superior wear resistance compared to conventional PVD coatings and addressing demands for extended tool life in industrial applications. Full article
(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials (2nd Edition))
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Review

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36 pages, 5138 KB  
Review
Coatings for Hydro Turbine Applications: A Materials Perspective
by Rodolpho Fernando Vaz, Marco León, Alessio Silvello and Irene Garcia Cano
Metals 2026, 16(4), 406; https://doi.org/10.3390/met16040406 - 7 Apr 2026
Viewed by 637
Abstract
Corrosion- and wear-resistant coatings are widely applied to hydro-turbine runners through thermal spray and cladding processes to enhance component efficiency and structural integrity by mitigating material loss during operation. This work provides a critical review of both mature and emerging coating materials, with [...] Read more.
Corrosion- and wear-resistant coatings are widely applied to hydro-turbine runners through thermal spray and cladding processes to enhance component efficiency and structural integrity by mitigating material loss during operation. This work provides a critical review of both mature and emerging coating materials, with particular emphasis on cermets, Fe-based amorphous alloys, high-entropy alloys, and functionally graded coatings. Their performance is analyzed in terms of wear, corrosion resistance, and applicability under hydro-turbine service conditions, highlighting the advantages and current limitations that hinder broader industrial adoption. The review identifies key challenges associated with materials chemistry, deposition processes, coating architecture, and cost-effectiveness, emphasizing the need for further advancements to improve coating reliability and competitiveness. In addition, a shift in coating design philosophy is proposed, moving toward a performance-driven and application-oriented approach in which coating properties are tailored to meet specific service demands through optimized material selection and process control. By integrating current knowledge and identifying critical gaps in the literature, this work provides a framework to guide future research efforts aimed at developing next-generation coatings for hydro-turbine applications. Full article
(This article belongs to the Special Issue Surface Treatments and Coating of Metallic Materials (2nd Edition))
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