Mechanical and Tribological Behavior of Carbon-Based Coatings Sliding against PEEK Polymer Counterfaces

E. BROITMAN; S. LAINO; S. SCHMIDT; P. FRONTINI; L. HULTMAN

Long Beach

Simposio; AVS 60th International Symposium and Exhibition; 2013

AVS

Carbon-based coatings are known for their good mechanical and tribological properties. By tuning the C sp3-to-sp2 bonding ratio and by alloying the carbon with other elements, it is possible to tailor hardness, elasticity, friction and wear resistance. Also, polyether-ether-ketone (PEEK) polymers are increasingly used by the industry because of their corrosion resistance, mechanical stability, and self-lubricating ability. Huge amount of data regarding their individual interaction with steel counterfaces is available; however, very little information is found regarding the interaction of both materials. In this work, we studied mechanical and tribological properties of carbon nitride (CNx) and carbon fluoride (CFx) coatings sliding against PEEK. The coatings were deposited on SKF3-steel balls by high power impulse magnetron sputtering (HiPIMS) using an industrial deposition system CemeCon CC800/9ML. CNx was prepared at room temperature (RT) and 180 oC (HT) by reactive sputtering from C target in a N2/Ar discharge at 400 mPa. CFx was prepared at RT by reactive sputtering from a C target in a CF4/Ar mixture at 400 mPa. PEEK 6 mm-thick unfilled plates were produced via injection molding (GATONE? 5600). The friction and wear properties were measured by a pin-on-disk device using 6.35 mm-dia coated and uncoated balls against PEEK in dry slide at pressure contacts from 860 to 1240 GPa. Optical and scanning electron microscopy, and EDX spectroscopy were used to observe the wear tracks and analyze the presence and composition of transfer films. A triboindenter TI-950 (Hysitron) was used to measure hardness, elastic modulus, and roughness of the materials. For uncoated steel counterfaces, the running-in friction (μ) takes place during the first 300 s, and shows peak values in the range 0.40-0.47. In the steady state, μ decreases to 0.30-0.35. The contact area shows big and deep scratches, oxidation, and no film transfer. RT-CFx and HT-CNx coatings have similar behavior. Both have running-in periods of 1000 s, μ in the range 0.25-0.45, which increases in the steady state to 0.45-0.50. The microscopy reveals that the coatings have failed; big wear scars and the presence of film transfer are easily observed. RT-CNx coatings show the best performance. At the end of 1000 s running-in period μ is in the range 0.25-0.33, and increases slightly to 0.35-0.38 after 6000 s. The coatings show a very small wear scar and the presence of film transfer. Our results demonstrate that a RT-CNx coating on a steel counterface sliding against a PEEK polymer improves the tribological behavior of the sliding couple, and also is advantageous due to the coating chemical inertness