IMPROVEMENT OF METAL PROPERTIES BY ION-IMPLANTATION

Ion implantation is being investigated as a technique for the beneficial modification of surface-sensitive and life-limiting properties of metals including resistance to wear and fatigue. Ion implantation is a process of accelerating ions to high velocities and directing them into the near-surface regions of materials (e.g. alloys) to produce in essence a different material (alloy) in the near-surface region. Ion implantation can produce a graded alloy from the surface to the unchanged underlying bulk alloys so that both the surface and the bulk alloys can be independently optimized. The implanted layer is typically hundreds to thousands of ångströms deep with implanted atom concentrations of up to fifty atomic per cent or more. The sliding-wear rate between various steel alloys was significantly reduced by implanting one of the surfaces with selected elemental species such as nitrogen, carbon and titanium. Experiments were conducted on a number of materials including stainless steel, too steel, bearing alloys and silicon nitride. The implantation technique has also been reported to increase fatigue lifetimes in low-carbon steel by a factor of 50-100. Experimentation is now being directed towards other materials of major technological interest such as titanium alloys. The effect of ion implantation on (1) the wear and fatigue properties and (2) the microstructural characteristics of implanted materials with selected examples is discussed. © 1979.