Physical foundations for surface treatment of materials with low energy, high current electron beams

The paper presents a review of original investigations on the surface modification of metallic materials with low energy (up to 40 keV), high current (up to 40 J/cm(2)) electron beams of microsecond duration. Based on materials research and on simulations of temperature and stress fields, the regularities and mechanisms for the changes in the defect structure and in the strain-stress state of pure metals (Fe) on pulsed heating are considered. The peculiarities of the formation of non-equilibrium structure-phase states and graded structures on pulsed melting of film-substrate (Fe-Ta, Al-Si, and Al-C) systems have been studied. For a broad spectrum of structural and tool materials (steels, aluminum and titanium alloys, hard alloys) it has been shown that the most pronounced changes in the structure-phase state occur in the near-surface layer quenched from the liquid state, where the velocity of the crystallization front reaches its maximum. In this layer, the second phases are partially or completely dissolved, and oversaturated solid solutions and nanosized second-phase segregates are formed. This substantially improves the electrochemical and strength properties of the surface layer. It has been established that the action of dynamic stresses has the result that the modified layer with enhanced strength properties is substantially thicker than the heat-affected zone. (C) 2000 Elsevier Science S.A. All rights reserved.