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UNDER HIGH INTENSITY ELECTRON BEAMS AND METROLOGY OF THESE BEAMS WITH A HELP OF MEMORY ALLOY TARGETS V. Prieb, "1st Memory alloys GmbH", Berlin, Germany (Proc. of the 2nd Int. Conf. "Radiation-thermal defects and Processes in inorganic materials, 14-19 August 2000, Tomsk", Tomsk, 2000, p.p. 10-13, Engl.) Abstract: Targets made of eutectic alloy Ni60Nb40, the austenitic homogenous alloy Fe-13wt%Mn and intermetallic equiatomic compound NiTi after the standard heat treatment with memory properties are irradiated with electron beams and investigated. Electron mono-impulse beams with the time length 50x10-9 s, the maximum current density 103 Axcm2 and the initial energy up to 250 keV have been used for the treatment of the target surface. The structure of irradiated and deformed (NiTi) specimens is investigated with a help of X-ray diffractometry. On the initial equilibrium Ni60Nb40 - specimen consisted in eutectic mix of two phase: rhombic one Ni3Nb and hexagonal one NiNb is observed a bright diffuse maximum that is typical for an amorphous phase with a large concentration of structural defects, but it can be seen selective maximums of the initial crystalline phases as soon as a larger new maximum corresponds to the fct-lattice of pure Ni and new reflexes corresponded to unknown phases of Ni-Nb-system. The irradiated target of the alloy Fe-13wt%Mn consist in the same γ-austenite that forms as usually from the α-phase at the thermal quenching and epsylon-martensite formed from the γ-austenite. The both examples show that during the irradiation can take place dynamic diffusion or a shear (martensitic) transformation between phases in the non-equilibrium state or the formation of new non-equilibrium phase. Irradiated NiTi-sample allows to measure the tensile-compression wave in the thin surface sheet with the length about 120 µm. Introduction: The modern surface treatment technology of materials with a help of concentrated energy streams bases on the modification of surface properties by the structural state change under high intensity photon, ion or electron beams. Perspectives of this technology are obviously connected with a formation of non-equilibrium structures in the surface sheet during the impulse treatment - the shorter impulse length, the more non-equilibrium states of a system and the brighter the property spectrum, correspondingly. The nanosecond impulse interval is the boundary case because it is near the characteristic time for the reaching of the total electron-phonon equilibrium. In the non-equilibrium state the electron subsystem temperature is above the phonon subsystem one, and the temperature of the whole system as a thermodynamics parameter has no sense. The structural changes are possible due to non-equilibrium energy exchange between "hot" electrons and "cold" phonons without of considerable heating of the target material. Experimental research of the super-short impulse action on the material surface is very difficult and it is impossible to observe the structural change in-situ during the radiation. It will be usually investigated the post-state of a target after the impulse switching out. Therefore, it is important that the target material be able to store the maximum of the information about processes during the radiation and to preserve (to memorize) this after the impulse switching off. Shape memory alloys are more perspective for this aim since they have a high structural sensitivity to different actions (temperature, stress, etc.) and short response time to them. It was the aim of this paper to investigate the formation of non-equilibrium structures in different metal alloys and to propose on this base an measuring method that connects the measured structural change with the impulse beam parameters. Conclusion: The structural changes take only place in the zone of immediate energy losses of the beam electrons. The mechanical stress distribution is the differential result of the energy losses distribution. That allows to determinate the qualitatively correspondence between the stress distribution on the memory-target and energy losses as soon as electron beam parameters. More: Article (full script, english) as PDF-file Home |