The microstructures and superconducting properties of MgB/sub 2/ tapes processed in-situ by a ball-milling method

Abstract

We investigated the microstructures and superconducting properties of MgB/sub 2/ tapes fabricated by an in situ powder-in-tube method using ball-milled powders. The ball-milling technique was briefly applied to various powders, such as Mg, MgH/sub 2/, and B powder, and to powder mixtures of Mg and B, MgH/sub 2/ and B, and Mg+B+SiC. They were heat treated at the relatively lower temperature of 600/spl deg/C for 1 hour under an argon gas atmosphere. Though the ball-milling had almost no effect on the critical current density (J/sub c/) values when we used MgH/sub 2/ powder, we did observe a clear effect for Mg powder. Significant enhancements of the J/sub c/ values were obtained for the ball-milled powders of Mg+B and Mg+B+SiC. For the latter powder, we obtained a J/sub c/ value of 1.2/spl times/10/sup 4/ A/cm/sup 2/ at 4.2 K and 10 T. Those values are nearly equal to the excellent values of the in-situ processed tape of MgH/sub 2/+B+SiC powder that was not ball-milled. The high J/sub c/ values may be due to the fine B powder abrading Mg particles in the ball-milling processing, thereby producing fresh Mg and B surfaces.