Research on Tribological Coatings

Dear Colleagues,

Friction and wear is one of the three principal failure modes (wear, corrosion, fatigue) of engineering components, causing substantial national economic losses in engineering applications. Therefore, technologies such as surface strengthening, remediation, and remanufacturing are crucial for overcoming wear-related issues in industry. Functional protective coating technology possesses "low input, high yield, and high environmental friendliness", which makes it an indispensable link between new remanufacturing technologies of surfaces and industry, thereby producing enormous economic and social benefits. The tribological characteristics of functional coatings are not one of their inherent characteristics; rather, they depend on the entire tribological system and are affected by numerous factors, including the preparation method, substrate, application conditions, working environment (temperature, humidity, loads, etc.). In recent years, researchers have conducted many experiments on coatings in order to better understand the fundamental principles of tribological coatings to reduce friction and provide lubrication. The key to the research lies in the preparation method, tribological characteristics, lubrication mechanism, functionality, environment-dependent characteristics, and design of advanced friction-reducing and lubricating coatings, etc. This not only improves the lubricating and friction-reducing characteristics of the coating, but also helps to improve the service life of the coating and reduce the economic loss caused by friction and wear.

The present Special Issue aims to highlight the recent advances in tribological coatings, and to provide researchers with the opportunity to publish their latest results, reviews, methods, and cases of engineering applications to further improve the research landscape and address the related problems of friction reduction and lubrication of coatings. We welcome the submission of high-quality original research papers and reviews. Research areas may include (but are not limited to) the following:

• Preparation methods for tribological coatings;
• Classification of tribological coatings;
• Microstructure, tribological and mechanical properties of tribological coatings;
• Lubrication mechanisms of tribological coatings;
• Wear mechanism of tribological coatings;
• Environment-dependent characteristics of tribological coatings;
• Functionality of tribological coatings (self-lubrication, self-adaptive, self-healing, self-organized);
• Application of tribological coatings.

We thank you for your interest and look forward to receiving your contributions.

Dr. Huatang Cao
Dr. Egemen Avcu
Dr. Feng Wen
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. Materials is an international peer-reviewed open access semimonthly 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.

• tribological coatings
• lubrication
• friction
• wear
• environmental self-adaptation
• functionality
• microstructure

Title: Enhancing the tribological properties of low-density polyethylene using hard carbon microfillers
Authors: Samuel Solomon; Rachel Hall; Jibao He; Vijay John; Noshir Pesika
Affiliation: Department of Chemical and Biomolecular Engineering, Tulane University, 6823 St. Charles Ave., New Orleans, LA 70118. (USA)
Abstract: The application of low-density polyethylene (LDPE) has been limited to packaging due to its inadequate mechanical and tribological characteristics. We propose enhancing LDPE by integrating hard carbon spheres (CS) to improve its strength, friction, and wear resistance. LDPE/CS composites were created by blending LDPE with varying CS amounts (0.5 – 8wt.%). Analysis using scanning electron microscopy and Raman spectroscopy confirmed CS presence in the LDPE matrix, with X-ray diffraction showing no microstructural changes post-blending. Thermal characterization exhibited notable improvements in thermal stability (~4%) and crystallinity (~7%), alongside hardness and Young’s modulus increases by up to 4% and 24%, respectively. Tribological studies on different composite samples with varying surface roughness under various load and speed conditions revealed surface roughness's pivotal role in reducing friction by decreasing real contact area and adhesive interactions between asperities. Increased load and speed amplified shear stress on asperities, possibly leading to deformation and failure. Notably, integrating CS in LDPE, starting at 1wt.%, effectively reduced friction and wear. The composite with the highest loading (8wt.%) displayed the most significant tribological enhancement, achieving a remarkable 75% friction reduction and a substantial 78% wear reduction.