Self-lubricating composite coatings: A review of deposition techniques and material advancement

This work is focused on creating coating layers made of a metakaolin-based geopolymer suspensions (GP)-formed Al matrix modified using H3PO4 acid with Al(OH)3 in isopropyl alcohol, named GP suspension I, and H3PO4 acid with nano Al2O3 in isopropyl alcohol, named GP suspension J. The selected GP suspensions were applied on aluminum and steel underlying substrates as single-layer coatings and multi-layer coatings, where multi-layer coatings included three and five layers that were polymerized by a curing process. Curing was divided into two types with every layer curing process and final layer curing process. For both GP suspensions I and J, the effect of the number of layers and the type of substrate on adhesion was investigated. The prepared samples on underlying substrates were characterized on the microscopy analysis including SEM for high-resolution images and 3D laser confocal microscopy (CLSM) for the 3D visualization of the coatings structure. Microscopy analysis showed structural defects such as porosity, cracks and peeling, which increase with a greater number of applied layers. However, these defects were only evident on a micro scale and did not seem to be fatal for the performance of the surface stability. The EDS mapping of the prepared layer showed inhomogeneity in the distribution of elements caused by the brush application. A grid test and thickness measurement were performed to complete the microscopy analysis. The grid test confirmed a very high adhesion of GP coatings on the aluminum substrate with a rating of one (only in one case was there a rating of two) and a lower adhesion on the steel substrate with the most frequent rating of three (in one case, there were ratings of two and one). The thickness measurement proved a noticeably thicker thickness of the prepared layer on the Fe substrate compared to the Al substrate by 20%–30% in the case of suspension I and by 70%–10% in the case of suspension J. The thickness of the layer also showed a dependence on the method of application and curing, as a thicker layer was always achieved when curing after the final layer of the GP suspension, compared to curing after each applied layer. The resulting single-layer and multi-layer thicknesses ranged from approx. 7 to 30 µm for suspension I and from approx. 3 to 11 µm for suspension J. A non-linear increase in thickness was also evident from the thickness measurement data.

Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Thickness, Adhesion and Microscopic Analysis of the Surface Structure of Single-Layer and Multi-Layer Metakaolin-Based Geopolymer Coatings

Jaskevic,

Novotny,

Mamon

et al. 2023

“…Self-lubricating coatings have been proven to provide decent outcomes in a wide range of technical applications. The application of these coatings modifies the microstructure, mechanical properties, and tribological performance of the contacting surfaces [27].…”

Section: Why Dlc Coatings?mentioning

confidence: 99%

Recent Progress on the Tribology of Pure/Doped Diamond-like Carbon Coatings and Ionic Liquids

Shaikh,

Sadeghi,

Cruz

et al. 2024

This review provides a comprehensive overview of recent advances in tribology concerning pure/doped diamond-like carbon coatings (DLCs) and ionic liquid (ILs) interaction. DLC coatings are often used in industrial machinery and processes where sliding occurs between surfaces, leading to wear and degradation of their surfaces. DLC coatings are optimized by adjusting operating and deposition parameters as well as doping them with other elements to improve performance, such as thermal stability and chemical resistance. ILs are a promising green lubricant option due to their low melting temperature, superior thermal stability, and high miscibility with organic substances. ILs have been studied as neat lubricants and additives, and their tribological properties have been investigated, including their use as extreme temperature lubricants. The tribological properties of pure/doped DLC coatings with ILs have also been explored, although limited research has been conducted in this area. The combined effect of DLCs and ILs shows great promise in reducing energy loss due to friction, promoting longevity, and conserving energy.

“…Therefore, studying the tribological properties of materials is crucial to reduce their surface friction coefficient and wear. Self-lubricating composite films are receiving increasing attention because of their excellent wear resistance and low coefficient of friction (COF) [3].…”

Section: Introductionmentioning

confidence: 99%

Tribological Properties of Hard TiB2 Thin Films Prepared at Low Temperatures Using HiPIMS

Yu,

Zhang,

Ying

et al. 2024

Magnetron-sputtered WS2 composite thin films are solid lubricants with excellent performances. However, the low hardness of the WS2 thin films necessitates the further improvement of their wear resistance. For this purpose, an effective strategy is to alternately deposit or code posit WS2 and a hard phase, such as TiB2, to form hard lubricant thin films. Herein, a TiB2 thin film was prepared under the same conditions as those used for depositing the WS2 thin film with a dense structure and excellent tribological properties. Because of the high deposition energy of high-power impulse magnetron sputtering (HiPIMS), the TiB2 thin film possesses a dense structure and leather-like flat surface (hardness = 24.17 GPa). The friction coefficient of the film under different loads ranges between 0.6 and 0.8. The wear rate of the thin film increases with load, mainly because of fatigue wear and abrasive wear. Under high loads, obvious furrow-like wear marks are observed. At different sliding frequencies, except 8 Hz, the friction coefficient of the film ranges from 0.6 to 0.8. The main wear mode is fatigue wear, particularly at increasing sliding frequencies. Although the film possesses a relatively high friction coefficient, its wear resistance is excellent (minimum wear rate = 1.96 × 10−6 mm3/(N·m)).