Abstract
The rapid adoption of the advantageous PEEK and its composites paired with steel counterparts in many tribological applications has prompted intense research to investigate their tribological properties under lubrication. This study investigated the effect of oil-lubrication and proposed a mechanism of action. Compared to the dry conditions, oil-lubrication with poly-α-olefin (PAO) base oils reduced friction, regardless of the type of polymer materials. However, the wear behavior depended on the polymer type; it increased for neat PEEK and decreased for PEEK composites. Additionally, the viscosity of the lubricant oils influenced the polymer behavior in distinct ways. These differences in tribological performance under oil-lubrication were explained by two important factors, the polymer transfer films on steel counterparts determined by Electron Probe Micro Analysis (EPMA) and the hardness modification of the polymer surfaces investigated by nanoindentation measurements. These factors were also related to each other, especially for PEEK composites.
Highlights
Polymers and polymer-based composites are often used in diverse tribological parts such as gears, bearings, bushings and seals in the automotive, aerospace and medical sectors
Oil-lubrication significantly reduced friction compared with dry conditions regardless of the polymer material, the effect of the viscosity grade of PAO on friction was found to depend on the polymer material
The wear tracks on the steel balls paired with carbon fiber reinforced (CFR) and glass fiber reinforced (GFR) PEEK looked polished with barely any polymer transfer film
Summary
Polymers and polymer-based composites are often used in diverse tribological parts such as gears, bearings, bushings and seals in the automotive, aerospace and medical sectors. Compared to metals, they are lighter, less noisy and have self-lubricating properties [1,2,3,4,5,6]. As polymers have lower mechanical strength and thermal stability than metals failure can result from wear, local melting and pitting when used under severe conditions [15,16,17,18]. Fiber reinforced PEEK composites such as carbon fiber reinforced (CFR) PEEK and glass fiber reinforced (GFR) PEEK are widely applied due to their improved mechanical prop erties [3,21,22]
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