The ex situ method yields MgB2 samples with high packing factor. However, the critical current density of MgB2 bulks and wires fabricated using the ex situ method (ex situ MgB2) requires improvement for practical use because of insufficient connectivity. In this study, we evaluated the microstructure of self-sintered ex situ MgB2 bulks fabricated from laboratory-made ball-milled powder. We observed that green compacts of the ball-milled bulks contain fine MgB2 grain aggregates and a decreased gap length between MgB2 grain aggregates compared with those prepared without ball-milling. Therefore, the number of connections between the MgB2 grain aggregates and current path increased. However, the width of the connections between MgB2 grain aggregates remained narrow, suggesting the importance of controlling the initial microstructure of green compacts, such as the size of MgB2 grain aggregates and packing factor, by optimizing milling and pressing conditions.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Electrical and Electronic Engineering