Chapter 18 - Corrosion- and Wear-Resistant Coatings Formed by Ion Beam Techniques

Abstract

This chapter deals with ion-beam-based methods for protecting metals. It is divided into two parts, corresponding to the kind of protection. One is protection against mechanical attack, or tribological protection. The attack takes place by one or many hard bodies in contact with the sample to be protected. Wear of the material induced by these counter bodies can be decreased when the material is treated by ion beam techniques. The other one is chemical protection, that is against corrosion. The corrosive medium is an aggressive aqueous environment such as an acid or a salt brine. The specimen is chemically changed or is consumed by the chemical reaction. Again, ion beam techniques can be used for protecting the material and increasing its lifetime in the corrosive environment. When a material is in contact with another one or another phase, it might be damaged by this contact by either mechanical or chemical effects. In most cases, contact and damage take place at the surface. The material communicates with its surrounding environment via its surface. Therefore, surface modification is a method to influence this communication and the performance of the material in case of an attack. Ion beam methods are, to first order, surface or near-surface modification methods. As such they have a potential to serve as a materials modification method for wear and corrosion protection. The techniques considered here are ion implantation and ionbeam-assisted deposition (IBAD) of thin films. Both work with a directed beam of energetic ions directed towards the surface of the material to be modified. In ion implantation, ions penetrate into a material and are incorporated. Apart from their presence there, they transfer energy and momentum into the material and may change physical structure and chemical composition. Ion implantation can be divided with respect to the energy of the ions. Roughly, three energy domains can be distinguished: low energy (several keV kinetic ion energy), medium energy (several 10–100 keV), and high energy (MeV). While medium- and high-energy ions are mainly used for ion implantation, the low-energy range is more relevant for IBAD. Here, a growing film is irradiated with ions. Again, they transfer energy into it and change its structure and phase, and elemental composition. Technically, ion implantation in the medium-energy range is most important. It is commercially being used. As mentioned above, the chapter is divided in two parts, each dealing with the protection to be exerted, chemical or mechanical. Each part is divided in sub-chapters according to the ion beam technique or ion energy regime used. Before discussing results from the literature, the measurement techniques for evaluating the effect of the ion beam treatment are described. Eventually, the last sub-chapter deals with industrial application of ion implantation.