Al2O3 + Graphene Low-Friction Composite Coatings Prepared By Sol–Gel Method

Abstract

In this work, Al2O3 + graphene coatings were prepared using the sol–gel method. The aim of the study was preliminary determination of the influence of size and amount of graphene nanoplatelets on morphology, chemical structure, and basic tribological properties of Al2O3 + graphene composite coatings. Two types of reduced graphene oxide (rGO) nanoplatelets with different lateral size and thickness were used to prepare the coatings. To characterize them, scanning electron microscope (SEM), glow discharged optical emission spectrometer (GDOES), Fourier-transform infrared (FTIR), reflectance spectrometer, and ball-on-disk tribological tests were used. It was found that the presence of graphene in the Al2O3 + graphene coatings did not fundamentally change the chemical transformation of ceramic Al2O3 matrix. Morphology examinations of coatings containing larger graphene nanoplatelets revealed a tendency to their parallel arrangement in relation to the coated surface. The tribological properties of Al2O3 + graphene coatings turned out to be strongly dependent on the size of graphene nanoplatelets as well as on the heat treatment temperature. The friction coefficient as low as 0.11 and good durability were obtained for the Al2O3 + graphene coating with larger nanoplatelets and heat-treated at 500 °C. The results of conducted research indicate the potential use of Al2O3 + graphene composite coatings prepared by the sol–gel method as low-friction ceramic coatings.

Functional Ceramic Coatings

“…This unconventional approach resulted in coatings with a layered microstructure, very low dry friction coefficient (0.13) and low linear wear. Interesting results were also obtained by Pietrzyk et al [10], who used the sol-gel method to produce Al 2 O 3 + graphene composite coatings on stainless steel substrates. The authors analyzed the influence of two types of graphene nanoplatelets (GNPs) and the parameters of coatings deposition on their microstructures and basic tribological properties, obtaining in some variants the dry friction coefficient of 0.11.…”

Morphology and Structure of Al2O3 + Graphene Low-Friction Composite Coatings

“…Oxide coatings have a potentially wide range of applications. The introduction of graphene to oxide coatings allows for a reduction in their friction coefficients: e.g., for Cr 2 O 3 coatings from 0.6 to 0.51 [18] and for Al 2 O 3 from 0.8 to 0.38-0.11 [15,16,19,20]. However, the tribological properties of coatings depend not only on the type of matrix, but also on the method and parameters of coating production and on the content of graphene [11,12].…”

“…Taking into account the morphology of the G1 rGO powder (Figure 2a), its tendency towards an anisotropic spatial orientation during the dip-coating deposition of the suspension on the substrate may translate onto the tribological properties of the coatings. These properties were previously investigated [15] in terms of the coefficients of friction Taking into account the morphology of the G1 rGO powder (Figure 2a), its tendency towards an anisotropic spatial orientation during the dip-coating deposition of the suspension on the substrate may translate onto the tribological properties of the coatings. These properties were previously investigated [15] in terms of the coefficients of friction (COF) and distances to failure on the friction path.…”

“…The use of graphene as a solid lubricant is based on a different friction-reducing mechanism, which takes advantage of the extremely easy glide between graphene flakes during incommensurate interface contact [6,[9][10][11] by the formation of multiple transferred Coatings 2022, 12, 1153 2 of 15 graphene nanoflakes on the asperities of sliding surfaces [12]. As the self-lubricating mechanisms of graphene operate independently of the presence of external lubricants, graphene can be used as a component of both bulk materials [13,14] and coatings [15][16][17][18][19][20][21][22][23][24]. The latter solution seems to be particularly promising, because graphene used as an additive in coatings displays various other characteristics, e.g., anticorrosive [25,26] or biologically active properties [27,28], allowing the achievement of a synergic effect with a properly selected matrix material.…”

“…Table 1. Average coefficients of friction (COF) and testing distances of various composite coatings containing graphene [15][16][17][18][19][20][21][22][23][24]. MgO/SiO + GO [22] Mg-Li alloy Micro-arc oxidation 0.15 >63…”