Fabrication and Characterization of Functionally Graded MgB 2 Superconducting Wires via Integrated Powder Metallurgy and PIT Approaches

In this study, functionally graded (FG) MgB 2 superconducting wire samples, with an external layer of 25 vol% B and 75 vol% Mg and an internal layer of 25 vol% Mg and 75 vol% B, were successfully synthesized via powder metallurgy by hot pressing at 400 MPa. Following the production step, the wire drawing process was performed, and the prepared samples were then subjected to sintering heat treatment at 700, 750, and 800°C for 2, 4, and 6 h. X-ray Diffraction (XRD) analysis was conducted to confirm the formation of the hexagonal MgB 2 phase throughout the wire samples, along with minor secondary phases. Scanning Electron Microscopy (SEM) and Electrical Resistivity (R-T) analyses were performed to investigate the effects of heat treatment temperature and duration on the microstructure and superconducting characteristics of wire samples. The obtained results revealed that higher sintering heat treatment temperatures and longer durations improved phase homogeneity and grain connectivity, as well as the superconducting performance of the wire samples, due to the narrowest transition width observed. Furthermore, the calculated activation energy (E a ) values for the synthesized wire samples demonstrated the effect of heat treatment parameters on vortex pinning characteristics. The findings of this research revealed that optimized fabrication parameters of MgB 2 superconducting wire materials were achieved at a synthesis temperature of 800°C with a 2 h sintering duration, successfully balancing the phase homogeneity, grain connectivity, superconducting performance, and flux pinning efficiency.