Friction and wear behavior of nitrogen ion implanted UHMWPE against ZrO2 ceramic

As the osteolysis induced by polyethylene wear debris is the main cause of long-term failure of total joint replacements, increasing the wear resistance of ultrahigh molecular weight polyethylene (UHMWPE) will be very important to obtain high quality artificial joint. In this paper, we performed nitrogen ion implantation on UHMWPE with ion doses of 5–125×1014/cm2. The surface hardness and contact angle on implanted UHMWPE surface were measured. A ball-slid-on-disc tribometer was run, as a comparative test method, to observe the tribological behaviors of ion implanted UHMWPE against ZrO2 ceramic in dry friction and plasma lubrication. Meanwhile, the profiles of the worn groove on UHMWPE surface were scanned. The experimental results demonstrate that nitrogen ion implantation enhances the microsurface hardness of UHMWPE. The wettability on implanted UHMWPE surfaces is improved. It is found that the friction coefficients of implanted UHMWPE obtain higher values than the untreated one. In plasma lubrication, the friction coefficients of untreated UHMWPE decrease, while the friction coefficients of implanted UHMWPE have little reduction except less fluctuation in wear process. It is shown that the wear rates of nitrogen ion implanted UHMWPE decrease with ion doses in plasma lubrication. In dry friction, however, the wear rates of implanted UHMWPE are 1.8–4.5 times higher than the untreated one. The wear mechanism of untreated UHMWPE is mainly adhesive wear, but the wear mechanism of implanted UHMWPE will shift to abrasive wear and fatigue wear.