Effect of Counterface surface roughness and its evolution on the wear and friction of PEEK and PEEK-bonded carbon fibre composites on stainless steel

摘要

The time-dependent variations in the dry sliding wear rate and friction of PEEK (450G and l00P) andcarbon fibre-bonded PEEK (APC2) on stainless steel (316S16) have been investigated and theevolution of wear scratches measured with optical profilometry. A three-pin-on-disk tester was used,operating at 0.18 ms{sup}-1, with a pressure of 1.0 MPa on 5 mm diameter pin. Specific wear rateswere calculated from mass lost by the pins at 15 km intervals and friction force was monitored by astrain-gauged torque beam. Two series of 90-km tests were performed for each pin/disk combination.The stainless steel disks had either a fine-ground or polished surface. The roughness of the groundstainless steel surface was chosen to coincide with the optimum value for low wear rate of the PEEKpins. To maximise pin/disk contact area, the PEEK and APC2 pin surfaces were run-in on 1000-gritsilicon carbide paper and ultrasonically cleaned in acetone before the first wear test. There was nosignificant difference in steady-state wear between these pins and those tested with as-mouldedsurfaces. The disks were analysed at 15 km intervals with the UBM profilometer, providing 3Dsurface scans and 2D profiles for roughness parameters without damaging the wear track. All thesurface roughness parameters reported in this work were produced from the UBM non-contactingoptical profilometer. A marked difference in specific wear rate was observed between the two typesof PEEK. The 450G had the lowest wear of 6×l0{sup}-6 mm{sup}3 N{sup}-1m{sup}-1 on boththe polished and ground counterface, whereas the l00P had wear factors of 1×l0{sup}-4mm{sup}3N{sup}-1m{sup}-1 on ground and 2×l0{sup}-5mm{sup}3N{sup}-1m{sup}-1onpolished stainless steel. However, the friction forces measured between the 450G PEEK and thepolished disk were up to three times higher than those against the ground disk, (0.35±0.01),decreasing to similar values as the polished surface became scratched. The APC2 pins showed verylittle difference in wear rate between the ground and polished disks. However, a steady decreasefrom 1×10{sup}-6 to 1×10{sup}-7mm{sup}3N{sup}-1m{sup}-1 over a distance of 90 km wasmeasured as more fibres were ground into a graphite transfer film lubricant and the coefficient offriction dropped from 0.35 to 0.18. The specific wear rates and coefficients of friction of the APC2samples were lower than those for PEEK, however, the APC2 caused more scratch deformation ofthe polished steel counterface.