ABSTRACf. Ion beam mixing is a new method which combines vapour deposition of thin layers and their subsequent bombardment using an inert-gas heavy-ion beam. The collision cascades induce intermixing between deposited layers and also with the substrate material. This method is capable of producing many alloy phases with no limitation of the alloy composition. The basic mechanisms of ion mixing have been extensively studied in recent years. Originally most of the attention has been focused on ballistic effects or radiation enhanced diffusion. However, it is now accepted that in the low or intermediate temperature range, where ion mixing is generally made, thermal spike mixing is the dominant mechanism and that chemical effects play an important role in phase formation. The different mechanisms of ion mixing will be presented and the main models reviewed and compared with experimental results. Of great interest is the formation of metastable or new alloys which could not be formed by conventional techniques. Typical examples of new metastable crystalline, quasi-crystalline or amorphous phase will be also presented.
. IntroductionBy using a well defined beam of ions, with energies in the range of some tens to hundreds of kiloelectronvolts, ion implantation allows the introduction of any element into any solid resulting in the formation of surface alloys. By this means, important modifications of various physical mechanical and chemical properties have been obtained and different industrial applications of ion implantation have been developed principally for wear reduction [1) in precision tooling and medical prostheses or for increasing corrosion resistance (2). However, most of practical applications to date have only involved high-dose nitrogen implantation because, for technical reasons, it is difficult to produce intense beams of metallic ions which are often required for industrial applications. Another interesting aspect is that ion beams deliver high energy densities over very short periods of time, thus it is possible to circumvent thermodynamic forces and produce new solid phases such as extended solid solutions or solid solutions of immiscible metals or also amorphous metallic alloys. Such amorphous coatings are very interesting from an applied perspective since these materials have several unique properties.Nevertheless, the maximum concentration of alloying element obtainable by ion implantation is physically limited by the sputtering effect. This surface erosion is caused by energy transfer to surface atoms in near surface cascades and the upper limit for the concentration of implanted atoms 527
