A novel powder-in-powder manufacturing approach for metal/ceramic (Cu/MgB2) superconductor wires: production and process characterization

Cu-MgB₂ wires are actively used in high technology equipment: coils of high magnetic fields in MRI machines, particle accelerators, fusion reactors, and magnetic levitation (maglev) systems. MgB₂ is a cost-effective superconductor with a high critical temperature (39 K) and Cu provides excellent formability, strength, and windability. Due to these properties, superconductors are produced using powder-in-tube (PIT) method: inserting metal/ceramic powders into a matrix tube and forming wires through rolling/drawing. However, PIT has shortcomings such as powder-sheath incompatibilities, secondary phases at the interfaces and a narrow material selection scope. This study explores and characterizes an alternative powder-in-powder (PIP) approach by optimizing extrusion parameters and leveraging the formation of dead metal zone (DMZ) during extrusion. Results showed that optimizing the extrusion parameters (450 °C, 85 MPa, die angle/extrusion ratio: 45°/4) and introducing a Cu bumper (45 %) behind the extrusion die assists inducing high friction at the DMZ and Cu powder interface. The friction causes inclusion of the powder and non-powder form of Cu bumper in the shear zone. The bumper is homogenously consumed to become the sheath of superconductor wires similar to the tube in the PIT method. Detailed microstructural characterization shows that the novel PIP method produces crack-free, windable wires with superconducting and structural properties comparable to those fabricated using the PIT method.