Improvement of tribological properties by ion implantation

Abstract

Many different measurements confirm that ion implantation changes the friction and wear behaviour, which are the most important properties of tribological systems. Unfortunately, these properties will not always be improved. In industrial application, very often different results of the effects of ion implantation into tools or machine components can be observed, even if the same materials are used. A very important reason for this is the different stresses on the tribological systems. Our own practical experience has so far proved ion implantation to be advantageous in the fields of cutting and milling tools, injection moulds, calibration tools for plastics extrusion, punches and dies, surgical instruments, and wear parts of combustion engines. Year by year, experience of the effective industrial use of ion implantation is gained. However, many investigations of tribometers and real engines using the on-line radionuclide wear measurement technique show us more and more that we are not yet able to understand the complicated physical and chemical reasons for the changes in tribological properties. We do not have a useful theory for the wear processes, so it is not possible to deduce the effects of ion implantation. Predictions can only be made from experience, and are poorly defined. This situation is the main reason for the slow introduction of ion implantation in industry. To find a new applicable theory of friction and wear, much more attention must be given to the following aspects of fundamental importance. o 1. (1) The energy input caused by friction, which is a function of the stress and other parameters of the tribosystem, within a short time leads to the appearance of energy islands, which are statistically distributed over the surfaces. The density of energy within these tiny energy islands is very high. 2. (2) One result of these high energy densities is a mutation of the material's composition and structure within a very thin layer of less than 100 nm underneath the surface. Another result is wear. 3. (3) Ion implantation also changes the composition and structure of the bulk material close to the surface. 4. (4) Together with the wearing surfaces, the mutating compositions and structures migrate into the depth of the material. Thus there is urgent need to increase our knowledge of the tribo-induced mutations of ion-implanted materials and their influence on the tribological properties. For that reason surface analyses have to be carried out to determine the composition and structure of the materials and the mutation caused by friction and wear. Complementary sensitive wear analysis will then enable new models and theories to be developed and corroborated. This is a difficult but interesting challenge to modern physicists, chemists and engineers.