Effect of mechanical alloying on the microstructure and properties of C-doped MgB₂ wire by Ex-situ process

We fabricated C-doped MgB₂ wires using the ex-situ process via the mechanical alloying (MA) technique to improve the doping effect and evaluated the effect of MA and C content on the phase formation, microstructure, and critical properties. The mixtures of MgB₂ and 0, 1, and 5 at% carbon black (CB) powders underwent MA using a planetary ball mill system for 25 hours. The powders were loaded into Fe tubes, drawn into wires, and sintered at 1000°C for 1 hour in flowing Ar gas. The MA process effectively induced fine and amorphous particles and led to C doping into MgB_2-x after sintering. The actual C content in samples with nominal 1 at% and 5 at% was 0.012 and 0.044 for MgB_2-xC_x, respectively, and this result was comparable to that of in-situ processed MgB_2-xC _x. The MA process and CB doping reduced the critical temperature (T_c-onset) but improved the critical current density (J_c) in high magnetic field. The MA-treated and 1 at% CB-doped wire exhibited a value of 4.1 × 10³ A/cm² at 6.4 T and 5 K, which was 5.9-fold greater than that of the untreated wire. This improvement was attributed to the lattice distortion, C doping effect, and grain refinement.