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. 2019 Dec 25;10(1):55.
doi: 10.3390/nano10010055.

Optimization of Process Parameters for a Chemi-Absorbed Graphene Coating and Its Nano Tribological Investigation

Pengfei Li  1   2 , Yuncheng Li  1 , Hongyue Chen  1 , Hui Liu  1 , Xianhua Cheng  2
Affiliations
Free PMC article

Optimization of Process Parameters for a Chemi-Absorbed Graphene Coating and Its Nano Tribological Investigation

Pengfei Li et al. Nanomaterials (Basel). .
Free PMC article

Abstract

A reduced graphene oxide coating was deposited on a titanium substrate for potential anti-friction applications in nano- or micro-mechanical systems. A γ-aminopropyltriethoxysilane coating was self-assembled on the substrate as an adhesive interlayer beforehand. The process parameters of self-assembly and hydrothermal reduction of graphene oxide coating were explored via water contact angle and tribological tests. Insufficient self-assembly duration of graphene oxide layer can be detected by water contact angle results, and the corresponding coating displayed a higher coefficient of friction and shorter anti-wear lifetime than the optimized one. Proper hydrothermal temperature and duration were also confirmed by its water contact angle, coefficient of friction and anti-wear lifetime. Noticeably, excessive hydrothermal temperature or duration would reduce the coefficient of friction, but diminish the anti-wear resistance. The optimized process parameters were confirmed as assembly duration of graphene oxide coating for 12 h, hydrothermal reduction duration of 6-8 h at 135 °C. Nano tribological behaviors of the obtained hydrothermal reduced graphene oxide coating by AFM tester were then investigated under various testing circumstances. The results showed that the coating performed reliable and low adhesion and friction forces under all circumstances. The nanowear resistance of the titanium substrate was significantly strengthened by the prepared coating.

Keywords: graphene surface coating; hydrothermal reduction; nano-tribology; process optimization; self-assembly.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
The influence of immersion time of GO assembly upon WCA values for GO-APS coating.
Figure 2
Figure 2
The influence of immersion time of GO on COF and Anti-wear lifetime of GO-APS coating on TNTZ alloy substrates.
Figure 3
Figure 3
The influence of reaction time for hydrothermal reduction upon WCA values for HRGO-APS SAM.
Figure 4
Figure 4
The influence of reaction time for hydrothermal reduction on COF and Anti-wear lifetime of HRGO-APS coating on TNTZ alloy substrates (a); COF vs time curves of coatings with three different reaction times—0 h (GO-APS coating), 10 h and 12 h (b).
Figure 5
Figure 5
The influence of reaction temperature for hydrothermal reduction upon WCA values for HRGO-APS coating.
Figure 6
Figure 6
The influence of reaction temperature for hydrothermal method on COF and anti-wear lifetime of HRGO-APS coating on titanium alloy substrates.
Figure 7
Figure 7
WCA data of hydroxylated APS coating, GO-APS coating and HRGO-APS coating (Insets are images of water droplets on tested surface).
Figure 8
Figure 8
AFM 3D morphology tests for (a) deposited Ti substrate, (b) GO-APS, (c) HRGO-APS (5 μm × 5 μm), and (d) HRGO-APS coating on the deposited Ti substrate (3 μm × 3 μm).
Figure 9
Figure 9
Typical data of deflection Error vs Z displacement curve obtained in adhesion force test.
Figure 10
Figure 10
Variation of the adhesion force of Ti substrate and prepared coatings with the change of applied load (with scanning rate of 2 Hz).
Figure 11
Figure 11
Variation of friction forces of Ti substrate and prepared coatings with the change of applied loads (with scan rate of 2 Hz; scan area: 2 μm × 2 μm).
Figure 12
Figure 12
Variation of the adhesion force of Ti substrate and prepared coatings with the change of sliding speed (applied load: 100 nN, Scan area: 2 μm × 2 μm).
Figure 13
Figure 13
Variation of the friction force of Ti substrate and prepared coatings with the change of sliding speed (applied load: 100 nN; scan area: 2 μm × 2 μm).
Figure 14
Figure 14
Variation of adhesion forces of deposited Ti substrate and prepared coatings under various RHs (Applied Load: 70 nN).
Figure 15
Figure 15
Variation of friction forces of deposited Ti substrate and prepared coatings under various RHs (Applied Load: 70 nN, Scan area: 2 μm × 2 μm, Scan rate: 2 Hz).
Figure 16
Figure 16
Variation of adhesion forces of hydroxylated Ti substrate and prepared coatings under various Temperature (Applied Load: 70 nN).
Figure 17
Figure 17
Variation of friction forces of hydroxylated Ti substrate and prepared coatings under various temperatures (applied load: 70nN; Scan area: 2 μm × 2 μm; scan speed: 2 Hz).
Figure 18
Figure 18
The effect of water molecules between contact surfaces in nanotribological tests.
Figure 19
Figure 19
Wear scars of samples: (a) deposited Ti substrate, (b) GO-APS coating and (c) HRGO-APS coating.
Figure 19
Figure 19
Wear scars of samples: (a) deposited Ti substrate, (b) GO-APS coating and (c) HRGO-APS coating.
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