Ion implantation has been shown to be an effective process for improving the wear, corrosion, and fatigue properties of metals. Characterization of surfaces which have been altered by ion implantation is difficult, because the properties vary with depth from the surface and because the affected material is at extremely shallow depths (on the order of 0.1 microns). Hardness testing provides a simple method for assessing the effectiveness of ion-implantation in improving certain properties of a metal. It provides information about increased strength near the surface, indicating possible improvements in wear resistance and/or corrosion resistance. The interpretation of such tests, though, is complicated by the fact that the properties of ion-implanted materials vary with depth from the surface.
Finite element simulation can enhance the understanding of hardness tests in surface-modified materials by providing a link between the results of the test and the actual changes induced by the implantation. It can, for instance, indicate the position of the peak in the hardness, relative to the position of the peak in the profile of the implanted ions, as studied by Was (1990). It can also be used to determine the change in the strength of the implanted material, by comparing the simulation to the test data [(Bourcier et al., 1991)]. This is made possible by the fact that the effects of ion implantation are modeled as a change in yield strength in the implanted region. The implantation hardens the surface both by producing damage in the lattice and by producing hard compounds such as nitrides and carbides, thus altering the yield strength in the implanted layer. This paper provides the results of a generic study of the simulation of ion-implanted materials, including a discussion of the error introduced by the discretization of the surface and the dependence of the depth of the peak in the measured hardness on the depth of the peak in the yield strength distribution.