TECHNIQUE FOR THE GROWTH OF METAL COATINGS BY ION-IMPLANTATION

Ion implantation of metals and non-metals is a recognized method for creating surface alloys and buried layers with unique and desirable properties. However, surface sputtering during implantation limits the maximum achievable atomic concentration to the point at which implanted atoms are sputtered away at the same rate as those being added. Since surface properties are often concentration dependent, the restriction of the maximum to less than the few tens of atomic per cent usually observed is a major constraint. A simple technique is described to produce an effective sputtering rate approaching zero by codepositing a sacrificial coating at a rate that just equals sputtering losses. This permits arbitrary surface alloy concentrations, allowing new uses for the existing base of ion implantation technology. A specific demonstration of the procedure has been made for ion implantation of tantalum into both M50 bearing steel and D2 tool steel. A buried layer of tantalum with a peak concentration between 50 and 60 at.% was achieved.