Introduction

ION IMPLANTATION involves the bombardment of a solid material with medium-to-high-energy ionized atoms and offers the ability to alloy virtually any elemental species into the near-surface region of any substrate. This near-surface alloying can be performed irrespective of thermodynamic criteria such as solubility and diffusivity. These advantages, coupled with the additional possibility of low-temperature processing, have prompted explorations into applications in which the limitations of dimensional changes and possible delamination of conventional coatings are a concern. In almost all cases the modified region is within the outermost micrometer of the substrate, often only within the first few hundred angstroms (i.e., microinches) of the surface. Maximum. concentrations of several tens of atomic percent are usually achievable, although this depends on the ion-substrate combination.

During implantation, ions come to rest beneath the surface in less than 10-12 s. This rapid stopping time produces an ultrafast quench rate in the wake of the stopping ion. This allows many novel surface alloys or compounds unattainable by conventional (equilibrium) processing techniques to be produced at room temperature. These include substitutional solid solutions of normally immiscible or low-solubility elements. Such highly metastable and amorphous alloys often possess unique physical and chemical properties. Ion implantation has been used extensively in the semiconductor industry since the 1970s to introduce dopant atoms reproducibly into silicon wafers to modify electrical performance, and it is used routinely in several stages of integrated circuit production. It allows fabrication of electronic devices not producible by any other process, largely due to the highly reproducible control of dopant concentration levels over several orders of magnitude as compared to doping by thermal diffusion. Since the mid-1970s, the use of ion implantation and other closely related ion beam processes has expanded into a number of diverse application areas in the international research and development community. However, only relatively recently have applications in the industrial sector developed.

Research interests in metals have expanded from the initial friction and wear studies to include other areas, such as corrosion, oxidation, fatigue, and studies of basic metallurgical mechanisms (Ref 1, 2). In addition to metals, polymers and ceramics have been studied with the principal aims of increasing the conductivity of polymers (Ref 3) and improving the fracture toughness and tribological properties of ceramics (Ref 4).

On a commercial scale, the applications for ion implantation of metals continue to increase, at present mainly for antiwear treatment of high-value components. A large number of industrial trials have involved the implantation of nitrogen for improving the wear resistance of coated and uncoated tools and other precision components. Implantation appears to be an attractive technique for treating industrial components by stabilization of the microstructure (preventing a change in wear mode), by transformation to a wear-resistant mode, or by chemical passivation to prevent a corrosive wear mode (Ref 5).

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