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Ion Implantation

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The ion implantation process has been developed to modify the surface properties of materials by using a combination of chemical and physical effects.

The material to be treated is bombarded by an intense beam of high energy ions (usually Nitrogen) which penetrate the surface, resulting in the build up of a subsurface zone of highly doped and compressively stressed structure.

The doping Nitrogen ions form very finely dispersed nitrides and there is consequently increase in surface hardness and wear resistance. The compressive stresses induced strongly resist crack propagation which further improves the durability of the treated surface.

Because the process does not rely on diffusion for the doping of Nitrogen into the surface, (all the energy being supplied by the very high kinetic energy of the ion beam) there is no need to heat the work piece and the process is carried out near room temperature. This means that very many materials which are not suitable for other surface enhancements techniques, such as PVD coating. can be successfully treated by Ion Implantation.

This process is particularly suitable for bio-implants as there are no compatibility problems or the risk of surface failure as there may be with coated parts. The benefit of ion implantation for the reduction of wear on the surface of prosthetic impnats in materials such as titanium and cobalt/chromium is now being demonstrated.

Applications

• Plastic Moulding Tools and Injection Screws
• Paper Slitting Tools
• Precision Press Tools
• Biomedical Implants

The principal applications for nitrogen ion implantation are in the improvements of surfaces subject to medium abrasive wear. The life of plastic moulding cores, cavities, nozzles and gate pads used for glass and mineral filled materials can be improved.

Implantation in hard chromium plating can substantially enhance the life of tools such as calibration dies and precision press tools.

Typically Materials, whose composition, surface finish or extreme value make then unsuitable for high temperature treatments, can be cost effectively enhanced by the II process.

Case Study of Ion Implanted Prostheses Material

Results

Changes in hardness were measured using nanoindentation techniques to porfile the hardness with depth. The implanted layer showed substantial increases in hardness (30 - 50%) to a depth of 0.1µm. It was also noted that the raised hardness extended well beyond the range of the nitrogen ions and is thought that this effect is due to the raising of compressive stresses in the near surface layers.

the ion penetration depth measured by Scanning Auger Microscopy (SAM) was approximately 0.15µm. The maximum nitrogen concentration was detected at a depth of 0.1 µm.

No changes in surface roughness were observed using Atomic Force Microscopy (AFM).

Measurements of contact angle of high purity water droplets were carried out and a significant reduction was observed on the implanted surface indicating an increase in wettability.

Treatment Conditions

Substrate Material CoCrMo

Surface Finish <0.05µm

Ion Dose 1 x 10^17 ions.cm2

Ion Energy 92keV

Ion Species N+ and N2+

Summary Conclusions

The implantation of Nitrogen ions in CoCrMo alloys has a beneficial effect on the surface hardness due to the introduction of compressive stresses and the formation of very finely distributed nitrides. The penetration depth is about 0.15µm and there is no change in the surface finish though wettability is improved.