  The powder-in-tube MgB2 wires were prepared by high energy milling of Mg and
B powder. The powder was not mechanically alloyed for 2h short milling time.
However, the MgB2 grains in wires are very small (20 100nm) and resembled to
the dimple after post-heat treatment. The clear evidence for transcrystlline
fracture is observed. It indicated that the grain connection was greatly
improved and the fluxing pinning was significantly enhanced. Another point to
view is no intermediate annealing was adopted during the whole rolling process.
The influence of the post-heat treatment on the transport current density was
studied. Despite the lower Tc of about 35K, the transport current density
reaches to 3X10E4A/cm2 at 15K and 3.5T for 700 sintered wires.

Superconductivity