PIT Processed ${\rm MgB}_{2}$ Thin Wires Sheathed With Stainless Steel

MgB₂ superconducting thin wires sheathed with stainless steel (SS) have been prepared by in-situ powder-in-tube (PIT) process. Using Magnesium hydride MgB₂ and amorphous B powders, SS sheathed MgB₂ thin wires have been fabricated through drawing to form the round wires of 0.20 mm ~ 0.10 mm in diameter. The SS sheath of 0.1 mm in diameter was hardened to be a Vickers hardness of around 600 HV through cold-working at room temperature without annealing. The heat treatment was performed at 630°C for 5 h in Ar gas atmosphere. The SS sheath recovered the hardness of 400 HV after heat treatment. The MgB₂ wires show the critical temperature (T_c) of around 35 K in onset and sharp transition of 2 K. The transport critical current (I_c) at 4.2 K and self-field are 40 A and 8 A for the MgB₂ thin wires of 0.2 mm and 0.1 mm in diameter, respectively. The I_c values correspond to the critical current density (J_c) of around 4,000-5,000 A/mm². The present MgB₂ thin wires with low thermal conductivity are promising as level sensors for liquid hydrogen and current leads with small heat leakage.