The microstructures and superconducting properties of MgB2 tapes processed in-situ by a ball-milling method

We investigated the microstructures and superconducting properties of MgB₂ 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, MgH₂, and B powder, and to powder mixtures of Mg and B, MgH₂ and B, and Mg+B+SiC. They were heat treated at the relatively lower temperature of 600°C for 1 hour under an argon gas atmosphere. Though the ball-milling had almost no effect on the critical current density (J_c) values when we used MgH₂ powder, we did observe a clear effect for Mg powder. Significant enhancements of the J_c values were obtained for the ball-milled powders of Mg+B and Mg+B+SiC. For the latter powder, we obtained a J_c value of 1.2×10⁴ A/cm² at 4.2 K and 10 T. Those values are nearly equal to the excellent values of the in-situ processed tape of MgH₂+B+SiC powder that was not ball-milled. The high J_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.