Carbon ion implantation of ultra-high molecular weight polyethylene using filtered cathodic vacuum arc with substrate pulse biasing

This paper discusses the results of an investigation that has been carried out to improve the nano-hardness and tribological properties of ultra-high molecular weight polyethylene (UHMWPE) using a filtered cathodic arc source with substrate pulse biasing. The filtered cathodic arc source generated highly ionized carbon plasma and ions were accelerated towards the substrate by the negative substrate pulse voltage. Graphitization, nano-hardness and wear rate of the modified surfaces were systematically studied as a function of pulse voltage (from - 3 kV to - 12 kV) and implantation time (from 1 min to 20 min). Graphitization of the modified surfaces was observed using Raman and X-ray photoelectron spectroscopes. The scanning electron microscopy images revealed heavy structural damage to the surface of the UHMWPE at increasing pulse voltages. The nano-hardness of the UHMWPE surface, measured at an applied load of 100 μN, was increased from 0.35 GPa to 1.6 GPa when implanted with carbon at a pulse voltage of - 10 kV for an implantation time of 12 min (ion dose about 1.73 × 10¹⁷ atoms/cm²). The wear test was carried out using a pin on disk tribometer with an applied load of 1 N for 1000 cycles, and showed a reduction in wear rate from 67.5 × 10^-5 mm³/Nm to 16.5 × 10^-5 mm³/Nm when a virgin UHMWPE was compared to a sample implanted with carbon at - 5 kV for 10 min. The mechanisms underlying the improved surface properties of the carbon-implanted UHMWPE were discussed.