Surface Engineering by Dheerendra Kumar Dwivedi

Author:Dheerendra Kumar Dwivedi
Language: eng
Format: epub, pdf
Publisher: Springer India, New Delhi

5.6.2 Ion Implantation

The basic principle of the process involves bombardment of high-energy ions on the surfaces of substrate to be engineered primarily to damage the regular arrangement (lattice) of crystalline structure of the metal for achieving amorphous structure, producing well-designed critical level of dislocation density, and forming unstable and stable phases or compounds based on the interactions between implanted ions and matrix material (Fig. 5.17). These changes in near-surface layers result in increase of hardness and resistance to wear and corrosion . However, the precise mechanism of improvement in the properties of modified surface through ion implantation is not very clear. The depth of modification of structure and implantation of ions (usually 1%) is generally limited to 1 μm and the same is determined by the initial energy of ions.

Ions are produced by thermo-ionic emission mechanism using any suitable gas. Moreover, nitrogen is one of the commonly used gases for ion implantation , and accordingly, it is called nitrogen ion implantation . Ions with appropriate energy levels are filtered and accelerated through utilization of electrostatic field, following which these ions are directed on the surface so as to have about 1% concentration below surface (up to about 1 μm) by using ions 1 × 1018 to 1 × 1021/m2.

Inherent nature of the process, that is, use of ionic bombardment only, offers many advantages over other competitive processes: (a) low-temperature exposure of modified surfaces, (b) no dimensional and geometrical variation, (c) no adverse effect on bulk material properties, (d) selective surface modification of functional areas only can be done, and (e) self cleaning process. However, this process finds very limited applications in the industry owing to (a) the need of expertise for designing the process, (b) limited depth of modified surface (about 1 μm) which becomes deficient for many high stress applications, (c) inaccessible areas cannot be modified as it is applicable only for areas in line of sight with respect to ion beam, and (d) requirement of expensive vacuum and equipment.

Fig. 5.17Schematic of ion beam implantation

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