The mechanical and tribological properties of ion implanted ceramics
The mechanical properties of ion implanted ceramics are primarily a function of the radiation damage produced by the implantation process. For crystalline ceramics this damage is chiefly nuclear displacements, though for glasses electronic effects have also been observed. In this study a number of single crystal and polycrystalline ceramics and a soda-lime-silica glass have been implanted with a range of ions in the energy range 90keV to 400keV and the changes in mechanical properties produced have been followed using hardness, indentation fracture and scratch testing. The damage structures which remain after implantation will control both the indentation hardness and surface fracture properties of cetamics. Changing the temperature of the substrate during implantation (in the range. 150K to 760K) has been found to alter this damage state and hence produce changes in the measured mechanical properties. In this temperature range, the effects of damage annealing at low doses were found to be minor for sapphire although for MgO damage annealing was found to result in a eduction of the radiation-induced hardening above 473K. The surface softening and stress relief accompanying amorphisation at higher doses was found to be strongly temperature dependent. Thus, the recrystallisation of amorphous material is important in determining the final mechanical properties of the implanted specimens. The tribological properties of the implanted ceramics were investigated using single pass scratch tests. Friction coefficients were found to increase with dose up to the onset of amorphisation, even when visible scratch tracks were produced. This increse is due to changes in adhesion between the slider and the flat induced by ion implantation. The reasons for these changes are as of yet unclear, though a possible explanation could be the removal of surface adsorbates which has been observed for MgO. Similar mechanical and tribological property changes observed for the polycrystalline ceramics as for the single crystal systems, but some extra effects were observed.