Chapter 6 - Surface Treatment of Materials with Low-Energy, High-Current Electron Beams

Abstract

During the last decade Proskurovsky and Ozur [1] ; [2] ; [3] at the Institute of High Current Electronics (Tomsk) have developed and built sources of wide-aperture (≥50 cm 2 ) low-energy (up to ∼40 keV), high-current (up to ∼50kA) electron beams (LEHCEBs) of microsecond duration, intended for surface treatment of materials. At the present time, these sources are superior in performance to other known sources of pulsed electron beams, pulsed lasers, sources of high-power ion beams, and pulsed plasma generators used for surface treatment. Important advantages of the LEHCEB sources are their reliability, high electrical efficiency, X-ray safety, and low cost. The promise of LEHCEBs as candidates for surface modification of materials is due to the following circumstances. The electron energy is absorbed within a thin (∼1 μm) surface layer, and this, in combination with the short pulse duration, allows one to realize pulsed melting and smoothing of the surface at rather low energy densities (2–5 J cm −2 ). As a result of the heat transfer into underlying layers of the material, the resolidification of the molten layer occurs at a cooling rate of ∼10 9 Ks −1 , which is high enough for nonequilibrium microstructures, including amorphous and nanocrystalline ones, to form. One can easily realize controlable evaporation of the near-surface layers by varying the energy density and the number of pulses, and this, in particular, makes it possible to efficiently clean the surface of oxides and other contaminants. Finally, pulsed melting of film-substrate systems allows one to produce nonequilibrium surface alloys. Thus, LEHCEB sources offer a unique tool for investigations in materials science and for developing new vacuum technologies for surface treatment of materials.