High-dose ion implantation of ceramics: benefits and limitations for tribology

Abstract

Ion implantation is known to be capable of modifying the surface and near-surface physical, chemical and mechanical properties of solids pertaining to hardness and wear. This paper is concerned with such effects of ion implantation into sapphire and soda-lime-silica glass. It establishes the complex interplay between radiation damage, hardness, surface stress and, for the first time, friction. For sapphire, both the shallow indentation hardness response and the integrated near-surface stress increase with damage and exhibit maxima as the surface eventually amorphizes. For the glass, initial damage is shown to result in structural softening before rehardening at higher doses. The radiation-induced stress in the glass is a complex function of dose and seems partly linked to electronic rather than displacement processes. Some structural change also eventually occurs in the glass akin to amorphization in crystals and is accompanied by changes in hardness and surface stress. Superimposed on these patterns of behaviour are changes in the friction behaviour, part of which is ascribed to increased adhesion presumed due to implantation changing the surface affinity for water adsorption. These effects are demonstrated and discussed in the context of ion-implanted ceramics finding application as controlled friction and/or wear components in engineering applications. A number of caveats are established for such applications. Other effects such as gas bubble formation, crazing and sputtering are shown to lead to surface microstructures which can also play a deleterious role in tribological behaviour. © 1988 Chapman and Hall Ltd.