Modification of metallic materials and hard coatings using metal ion implantation

Ion implantation, with doses in the range 10¹⁶ to 10¹⁸ ion cm^-2, modifies the surface properties of many metallic and ceramic materials. Whilst gas ion beams are currently employed extensively, metal ion implantation (Mil) systems have been developed based on the vacuum metal arc and a brief review of these systems is presented. Examples of industrial applications are given using, primarily, Mo ions which harden the surface of steel, increase its corrosion resistance and lower the coefficient of friction of the alloyed (or implanted) zone, IZ. Extending well beyond this zone, a dislocation network is developed which hardens the material in depth. Termed the long-range effect, this occurs in alloys and in low ductility materials such as TiN. Microstructural studies of TiN coatings after Mil are presented together with a model for the development of this effect. The results show that the stress field in TiN made by PVD is modified by implantation but no effect on the grain structure is found, whereas in TiN made by CVD the residual stress is not changed but growth of fine grains within the original grain structure is observed.