Modern Methods of Shaping the Structure and Properties of Coatings

1. Introduction

This Special Issue, entitled “Modern Methods of Shaping the Structure and Properties of Coatings”, includes ten research articles. It presents the latest developments in the fields of shaping the properties of surface layers, modern technologies relating to coatings, and advanced metallic and composite materials, which represent key areas in surface engineering. The main topics covered by these articles include the phenomenon of surface wear due to friction, erosion, and corrosion and modern methods of applying coatings and shaping the properties of surface layers, including PVD, electrofriction treatment, zinc coatings, TiN/Ti layers, self-healing coatings, thermal spraying of high-entropy composite coatings, arc cladding of nickel-based alloys, and thermal spraying. This Special Issue provides valuable knowledge based on analytical and empirical studies related to coating technologies, shaping the properties of coatings and surface layers, and advanced methods of characterizing materials and coatings, and also concerns in-depth analysis of wear phenomena.

The phenomenon of the surface wear of machine parts on the surfaces of kinetic nodes and tool wear as a result of the impact of environmental factors and working conditions involving friction, erosion, cavitation, and other factors is natural. However, the wear of machine components and tools leads to a decrease in their operational parameters and ultimately to a need to repair or replace these components [1,2,3].

For this reason, various technologies and methods have been used to improve the operating parameters of working surfaces and to increase the durability of components and entire machines and devices already at the production stage. Various methods of surface treatment and protective and anti-wear coatings are used in production processes [3,4,5].

However, due to the growing awareness of the need for the rational management of non-renewable resources, energy, and raw materials, efforts are being made to improve energy efficiency and the operating parameters of machines and devices.

Increasing the operating parameters of devices, including energy devices such as combustion or electric engines, causes an increase in the loads on the components in the working cross-section and on the working surfaces.

Therefore, new solutions are constantly sought after in the field of materials, coatings, and manufacturing methods, including methods for shaping the properties of surface layers and applying coatings with special properties [6,7].

Surface engineering can be divided into two main areas. The first involves shaping the properties of the surface layer by changing its structure, microstructure, or chemical and phase composition. These include various surface treatment methods, such as surface hardening, or thermochemical treatments, such as surface alloying, including the widely used method of nitriding.

The second area is the application of coatings to the component substrate. Here, in turn, we can distinguish many different sub-areas and methods that allow for the deposition of coatings on various scales and with different thicknesses, from micrometres to even centimetres.

Modern coating technologies are fundamental to contemporary surface engineering, providing protection, functionality, and enhanced durability for components exposed to extreme conditions [3]. In recent years, there has been a dynamic development of methods enabling the precise micro- and nanoscale structural shaping of coatings, which directly translates into improved mechanical properties and wear and corrosion resistance.

One of the most interesting achievements in modern surface engineering and materials engineering is the development of coating properties such as self-healing (repairing) capabilities and antibacterial functions or biocompatibility [8,9]. Rising industrial demands, especially in the automotive, aerospace, marine, and machinery sectors, and also the necessity for sustainable development and environmental protection, are driving the implementation of innovative technological solutions.

Modern methods of coating deposition and modification include, for example, advanced thermal spraying such as high-velocity oxy-fuel (HVOF), plasma spraying and cladding, and laser surface treatment and cladding [4,5,10]. These are supplemented by micro- and nano-structural modifications and hybrid processes that can combine mechanical and chemical surface engineering [11,12]. Technologies like electrofriction treatment and electrotribological modifications are increasingly being utilized to harden surfaces and improve wear resistance [4]. Simultaneously, the application of multicomponent high-entropy alloys (HEAs) offers coatings with unprecedented durability and corrosion resistance due to their unique microstructures [10,13,14,15]. Nanomaterials and polymer–ceramic composites further enrich the portfolio of functional coatings, enabling properties like self-healing and antibacterial activity [8,16,17].

The growing role of numerical simulations and artificial intelligence in optimizing coating processes and designing materials is emphasized in the literature, offering integrated approaches that combine advanced deposition techniques with multidimensional analysis to open new frontiers in surface engineering [18].

Additive technologies and methods for manufacturing coatings, especially cladding, are currently gaining particular importance. There are various different methods for the additive manufacturing of coatings, repairing components (build-up), and also for manufacturing entire 3D components. In the case of additive manufacturing, the quality and finishing of the surface are decisive for the potential applications [19,20,21].

Currently, various technologies and materials are available that allow for shaping the properties of the surface layers of components, but the key to ensuring correct operating parameters and durability is knowledge of the operating conditions and environmental factors that affect the material.

2. Short Characterization of the Special Issue

This Special Issue collects research articles and studies that demonstrate novel approaches to modifying the microstructural, mechanical, and functional properties of surface layers and coatings. It encompasses both experimental and simulation-based works, exploring the influence of processing parameters, substrate conditions, and chemical and phase composition on the performance and durability of the components.

In many of these studies, the authors refer to the principles of sustainable growth, the benefits of using hybrid methods, i.e., combining different methods in one process, advanced methods and techniques for testing materials and coatings, as well as the correlation between the structure and microstructure of coatings and their properties and performance parameters.

The studies presented in this collection offer new perspectives for industrial implementation, as well as academic research.

This Special Issue features ten articles covering a broad spectrum of coating materials and deposition techniques. The work “Effect of Electrofriction Treatment on Microstructure, Corrosion Resistance and Wear Resistance of Cladding Coatings” by Zhuldyz Sagdoldina et al. demonstrates the synergic effects of combining induction coating with electrofriction treatment (EFT) on L53 steel, resulting in a fine-grained dendritic microstructure and hardness of up to 965 HV. This hybrid method substantially enhances wear, erosion, and corrosion resistance, making it especially valuable for agricultural machinery and applications requiring durable working tools [4].

In the paper “Physical-Vapor-Deposition-Coated Natural Rocks as Sustainable Cutting Material: First Insights into the Effect of Substrate Integrity in Properties of TiN Thin Film”, the authors investigate TiN films deposited on natural stones via PVD, aiming to develop a sustainable alternative for cutting materials. Surface integrity and micro-topography were found to have a significant influence on coating adhesion and uniformity [5].

The paper “Dual Microcapsules Encapsulating Liquid Diamine and Isocyanate for Application in Self-Healing Coatings” presents a polyurethane–epoxy system containing microcapsules that enable autonomous scratch repair. The coatings achieved self-healing efficiencies exceeding 30%, making them highly promising for corrosion protection [8].

The paper “Study on the Self-Repairing Effect of Nanoclay in Powder Coatings for Corrosion Protection” demonstrates that nanoclay-modified polyester coatings possess self-healing ability due to the swelling of montmorillonite particles, which improves their electrochemical stability and corrosion resistance [9].

Kiape S. et al. present the manuscript titled “CoCrFeMnNi0.8V/Cr₃C₂-Ni20Cr High-Entropy Alloy Composite Thermal Spray Coating: Comparison with Monolithic CoCrFeMnNi0.8V and Cr₃C₂-Ni20Cr Coatings”. The authors compare HEA-based composite coatings to monolithic ones produced by HVOF spraying. The hybrid structures exhibit superior corrosion and wear resistance, confirming the synergistic benefits of combining ceramic and metallic phases [10].

Sfikas A.K. et al. explore the relationship between spraying temperature and phase evolution in the manuscript “Microstructural Evaluation of Thermal-Sprayed CoCrFeMnNi0.8V High-Entropy Alloy Coatings”. The authors observe that higher spraying temperatures promote the coexistence of FCC and BCC phases, optimizing mechanical and tribological performance [13].

The authors of the article “Effect of Ultrasonic Vibration on Microstructure and Antifouling Capability of Cu-Modified TiO₂ Coating Produced by Micro-Arc Oxidation” investigate the impact of ultrasonic vibrations introduced during the MAO process. They show that the treatment resulted in increased coating thickness, higher copper incorporation, and improved antifouling behaviour [16].

The authors of the paper titled “Simulation of TiN/Ti Multilayer Coating under the Impact of Multiple Particles Based on Cohesive Element” use cohesive element modeling to simulate stress evolution and crack propagation in multilayer coatings exposed to multiple-particle impacts. The analysis provides valuable insight for optimizing erosion-resistant designs [18].

In the study “Quality of Zinc Coating Formed on Structural Steel by Hot-Dip Galvanizing after Surface Contamination”, Vontorová J. et al. examine the effects of surface impurities on the galvanization process. The authors point out that even minor contamination led to poor adhesion and discontinuities, highlighting the critical importance of surface preparation before coating [22].

In turn, Kihara E.A. et al., in their manuscript titled “Effect of the Shielding Gas and Heat Treatment in Inconel 625 Coatings Deposited by GMAW Process”, study how variations in shielding gas and post-deposition heat treatment affect the microstructure and hardness of Inconel 625 coatings. They demonstrate that the optimal parameters provide microstructural uniformity and high mechanical performance [23].

In summary, these studies collectively confirm that modern coating and surface modification methods enable tailored materials with unique properties fit for highly specialized and extreme operating conditions. The integration of thermal spray techniques, microstructural engineering, and the application of advanced alloys and nanomaterials opens up promising areas in surface engineering. This Special Issue offers valuable guidance for researchers and engineers aiming to develop and implement coatings characterized by high strength, durability, self-healing, and sustainability.

The presented works provide a strong foundation for advancing coating technology research and development, emphasizing deposition process optimization, micro- and nano-structural control, and comprehensive functional property characterization. This collection of studies holds significant relevance for many branches of industry like the machinery, transportation, and aerospace industries and other sectors where advanced metal alloys and composites are used, presenting broad practical application potential, as well as options for new implementations.

The studies presented in this Special Issue collectively highlight the importance of combining theoretical understanding with technological innovation. Through the integration of modelling, experimental optimization, and advanced materials, the research fulfils the gap between laboratory-scale studies and industrial applications. The use of hybrid coatings, self-healing systems, and high-entropy materials represents a forward-looking approach to the design of next-generation protective layers.

3. Concluding Remarks

This Special Issue contains 10 articles, but it should be noted that the total number of manuscripts submitted was greater. Unfortunately, not all of these passed the rigorous peer-review process.

The wide range of experimental, numerical, or analytical studies conducted and presented by 61 authors, representing international research teams from around the world (Kazakhstan, Germany, Czech Republic, China, Greece, the UK, Brazil, and Canada) proves the topicality and importance of this Special Issue.

A scientific article is a natural consequence of research. It is the culmination of often lengthy and complex design, technological, and laboratory work, and ultimately, the analysis and interpretation of the results.

In turn, the journal Coatings, thanks to its open access model and Special Issue initiative, is an excellent platform for academic discussion and the exchange of valuable information on the latest trends and research results.

As Guest Editors, we would like to congratulate all of the authors on their valuable articles and thank them for choosing Coatings and our Special Issue to present their research findings and results. We wish all the authors continued success in their research, and hope that their work attracts numerous citations.

We are also pleased to share that, due to the success of the current edition of Special Issue, we and the Coatings Editorial Team have decided to continue exploring the topics covered in this Special Issue in a second edition.

Therefore, we encourage authors to continue their collaboration with Coatings.