Insights of the Ultralow Wear and Low Friction of Carbon Fiber Reinforced PTFE in Inert Trace Moisture Environment

Abstract

Ultralow wear rates and low friction have been observed for carbon fiber reinforced PTFE (CF/PTFE) when sliding against steel or cast iron in dry gas environments. Although the strong environmental sensitivity of this tribosystem is well known, the origin of the outstanding tribological performance in dry gas remains unanswered. Some researchers attribute the low friction and wear to the formation of carbon-rich surfaces in the absence of oxygen and moisture in the environment. However, low friction between carbon surfaces is generally dependent on moisture. In this paper, extensive analyzes are conducted on the tribofilms formed on the CF/PTFE surface and the steel counterface after sliding in a high-purity nitrogen environment. TEM analysis of a cross-section of the tribofilm on the steel surface reveals that the sliding surface consists mainly of iron (II) fluoride and not carbon, even though a significant amount of carbon was observed near the surface. XPS and TEM analysis further revealed that the tribofilm formed on the worn composite surface consisted of nanoparticle agglomerates, anchored to the PTFE matrix and to each other by carbon with turbostratic structure. Turbostratic carbon also formed an ultrathin and surface-oriented superficial layer on top of the agglomerates. Governing mechanisms of the low friction and wear of the CF/PTFE—steel tribosystem were investigated by complementary tribotests with pure graphite samples and MD simulations of the identified surfaces. These indicated that the low friction between the carbon and iron fluoride in the tribofilms is due to poor adhesion between the distinctly different surfaces. Graphical Abstract

Effect of Oxygen and Moisture on the Friction and Wear of Carbon Fiber-Reinforced Polymers

“…The counterface discs were machined from 34CrNiMo6 alloy steel with a hardness of 460 HV. This material has been extensively studied as a counterface material for CF/PTFE composites and has shown favorable results [7,9,18]. The counterfaces were grinded to a surface roughness of S a = 0.12 ± 0.02 µm and a random texture, using 400 p silicon carbide abrasive paper in a figure-eight motion.…”

“…The friction and wear of PTFE composites filled with carbon fiber or other carbons are currently unchallenged in dry gas environments compared to other fillers [5,6]. The mechanism behind the great tribological performance of CF/PTFE sliding against steel in dry gas has recently been discovered by the authors [7]. In high-purity nitrogen, a super smooth iron fluoride film is tribochemically formed on the steel surface, which has poor adhesion to the non-graphitic carbon film that is formed on the CF/PTFE surface.…”

“…Extensive research has been carried out by Johansson et al on the tribology of CF/PTFE in dry gas environments, e.g., [7,9,18]. This paper aims to extend the investigation to CF/PEEK and compare the tribological behavior of the two materials in gas environments with different amounts of moisture and oxygen.…”

A Systematic Review of the Recent Advances in Superlubricity Research

“…Many scholars at home and abroad have made important contributions to the development of this direction. Luo's group discovered several water-based liquid very-low-friction systems [97,98], and Liu and Zhang's group discovered an amorphous, fullerene-carbon film, solid, very-low-friction system [99]. Direct experimental determination of the dissociation energy of graphene in self-retraction motion was independently achieved by E. Koren's group [100] and Quanshui Zheng's group [101].…”

Dry Friction and Wear Behavior of Laser-Sintered Graphite/Carbon Fiber/Polyamide 12 Composite

“…However, so far, very little has been reported regarding the tribological characteristics of a reinforced thermoplastic filled with a solid lubricant, and very few articles among them are concerned with composites prepared by the SLS technique [15,[24][25][26]. The few reported results showed that inclusion of either PTFE or MoS 2 could effectively reduce the coefficient of friction of laser-sintered PA12 by forming a homogenous transfer film on the counter-surface [15,27], and that a 5-10% weight fraction of graphite was sufficient to significantly improve the tribological characteristics of PA6 [24].…”