Mechanically Alloyed MgB_2 Superconductors: Microstructure, Tape Formation and Critical Currents

摘要

The recently detected superconductor MgB_2 shows the highest critical temperature (up to 39 K) of any intermetallic phase. Therefore, it is a candidate for applications in power engineering at 20 K using cryocooling. The application of mechanical alloying (MA) for the preparation of MgB_2 powder and its use in tape fabrication is shown to be an optimal tool to obtain an enhanced magnetic flux pinning by a combination of microstructure refinement as well as an exact control of the stoichiometry of the MgB_2 compound. Partially reacted MA powders are used for tape fabrication by the powder in tube (PIT) technology. Despite slightly reduced T_c values of about 32 K, maximum critical current densities of 35 and 9 kA/cm~2 in external magnetic fields of 7.5 and 10 T, respectively, are achieved at 4.2 K.