The Effects of Ion Implantation on Friction and Wear of Metals

The effects of ion implantation on the friction and wear behavior of metals were investigated. Experiments were conducted with iron, titanium, and copper implanted with nitrogen ions, iron implanted with aluminum ions, and copper implanted with zinc ions. The significant reduction in friction and wear of the iron and titanium systems is attributed to a hard layer formed during the ion implantation process. This hard layer minimizes plowing and subsurface deformation and hence reduces the delamination wear process, i.e., crack nucleation, crack propagation, and the formation of delamination wear sheets. The implanted copper specimens did not appear to have a hard surface layer and showed little improvement in their tribological behavior over the unimplanted copper. Iron implanted with nitrogen ions was compared with ion nitrided iron. Under dry sliding conditions and high loads ion nitriding appears to be superior to ion implantation. However, at lower loads and under lubricated conditions, ion implantation is more advantageous due to its superior surface finish. A finite element model of an elastic semi-infinite solid under the contact of a stationary rigid asperity showed that the hard layer does not change the subsurface stress distribution. Therefore, the role of this thin layer is not to support the load, but to decrease the plowing component of friction, which, in turn, substantially reduces subsurface deformation and thus wear.