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 modif ication 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 materia ls research and on simulations of temperature and stress fields, the regula rities and mechanisms for the changes in the defect structure and in the st rain-stress state of pure metals (Fe) on pulsed heating are considered. The peculiarities of the formation of non-equilibrium structure-phase states a nd 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 to ol materials (steels, aluminum and titanium alloys, hard alloys) it has bee n shown that the most pronounced changes in the structure-phase state occur in the near-surface layer quenched from the liquid state, where the veloci ty of the crystallization front reaches its maximum. In this layer, the sec ond phases are partially or completely dissolved, and oversaturated solid s olutions and nanosized second-phase segregates are formed. This substantial ly improves the electrochemical and strength properties of the surface laye r. It has been established that the action of dynamic stresses has the resu lt that the modified layer with enhanced strength properties is substantial ly thicker than the heat-affected zone. (C) 2000 Elsevier Science S.A. All rights reserved.