Effect of Normal Load and Rotational Rate on the Coefficient of Friction of CoCr Alloy in Hyaluronic Acid as Lubricant

Abstract

The effect of normal load and rotational rate on the coefficient of friction (COF) of CoCr sliding against alumina was evaluated using a pin on disk tribometer. Tribological tests were carried out by using CoCr disks of 38 mm diameter and alumina balls of 6 mm diameter as counterpart (pin). An aqueous solution containing 3g/L of HA, concentration equivalent of that found in the synovial fluid, was used as lubricant and it was in continuous recirculation throughout the test. The COF values for two normal loads, 1N and 5N, and two rotational rates, 60 rpm and 120 rpm, have been obtained for a constant sliding distance of 500 m. The tribological tests were performed in duplicate in order to verify the reproducibility of the results. The results show that the COF varies with the load and with the rotational rate, so that, for the same load, the COF increases as the rotational rate decreases. This effect is more significant at lower loads. Meanwhile, the COF values are higher for loads of 1N than for 5N regardless of the rotational rate. The wear tracks were observed by optical microscopy and the images revealed the widest tracks at 5N and 60 rpm.