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Research project: Lubrication of PEEK and its composites with steel counterparts

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Due to their lightweight, reduced noise and self-lubricating properties, polymers and polymer-based composites are becoming preferred materials in many tribological parts in automotive, aerospace, medical, industrial applications. On the other hand, the mechanical strength and thermal stability of polymers are lower than those of metals, and therefore they tend to suffer from failures such as wear, local melting and pittin. Poly-Ether-Ether-Ketone (PEEK) and its composites have superior mechanical properties and higher thermal stability than other conventional polymers which make it suitable for tribological applications operating under severe conditions. In practice PEEK is commonly used with steel counterparts in dry conditions due to its self-lubricating properties, but fluid lubrication has the potential to further reduce friction and wear of PEEK. The aim of this study is to elucidate the effect and mechanism of lubrication on tribological properties of PEEK and its composites.

Tribological tests are carried out at ambient temperature using a Mini Traction Machine (MTM) from PCS Instruments Ltd. in three configurations, PEEK-steel, PEEK-PEEK and steel-steel, as shown in Fig. 1. The tests are performed under two different types of contact motion, sliding and sliding-rolling, and use smooth and rough balls.

Apart from friction, the study involves the measurement of wear profiles of PEEK plates with a stylus profilometry and hardness of PEEK as a function of indentation depth performed with a nanoindenter. The carbon mapping and analysis of polymer transfer films found on the steel balls after tribological tests are carried out with Electron Probe Micro Analysis (EPMA) (Fig. 2) and Raman spectroscopy.

Fig.1.  MTM set-up and configurations
Fig.1. MTM set-up and configurations
Fig. 2.  EMPA carbon maps of rough steel balls paired with PEEK in dry and PAO4 lubricated conditions

Fig. 2.  EMPA carbon maps of rough steel balls paired with PEEK in dry and PAO4 lubricated conditions

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