LASER PROCESSING OF NB3AL(GE, SI) HIGH-FIELD SUPERCONDUCTORS

The laser irradiation process is a promising method for the fabricatio n of metastable Al5-Nb3Al(Ge,Si) compounds. Thereby Nb-sheathed Nb-25 at. %Al(Ge,Si) microcomposite tapes are prepared by a conventional pow der metallurgical method and heat treated by a high-intensity CO2-lase r beam. The parameters selected during laser beam irradiation of the c omposite determine the relative amounts of molten, heat-affected or un reacted material. In order to obtain large overall superconducting cur rents, it is favorable to melt a large fraction of the microcomposite without melting the surrounding Nb sheath. The cooling rate after lase r beam irradiation determines the structure and the formation of metas table phases in the resolidifying material. The sequences of the proce ss are simulated by heat flow calculations, which consider laser power , beam diameter, tape velocity, thickness, and microstructure, as well as heat transfer coefficients. From these calculations we could deduc e optimum conditions for the laser treatment, leading to J(c) values o f 10(5) A cm-2 at 10 T and 10(4) A cm-2 at 16 T.