The effects of ion implantation on the friction behaviour of sapphire

The friction behaviour of ion-implanted sapphire in contact with diamond cones and spheres of a range of materials has been investigated as a function of implantation dose and implant species. Generally, an increase in friction is observed at low doses followed by a decrease once amorphization takes place. For the sharp diamond cones this can be correlated with changes in ploughing behaviour controlled by near-surface plasticity, whereas, for the spheres, the increase in friction for low-dose implants is due to changes in adhesion between the spheres and the implanted layer. The implications of these observations for the creation of lubricating surface layers by high-dose ion implantation are discussed.