Manufacture and superconductivity of tantalum matrix RHQT processed Nb3Al superconductors

The replacement of Nb matrix with Ta for rapid-heating, quenching and transformation annealing (RHQT) processed Nb₃Al conductor seems to be advantageous for facilitating the RHQ operation due to a higher mechanical strength at elevated temperatures and less reactivity with the molten Ga in the quench bath and suppressing flux jumps in low magnetic fields. We have fabricated three grades of the Ta matrix precursor, in which the volume fraction of Ta matrix is different, so as to examine the drawability of such Ta matrix precursors. Also examined are the effects of using the Ta matrix on the RHQ condition, T_c values after quenching and subsequent annealing, respectively, J_c (core), overall residual resistivity, and magnetization curves. We have succeeded in drawing all of Ta matrix precursors and confirmed the favorable existence of a plateau region in the I_RHQ-T_c relationship even for the Ta matrix RHQT Nb₃Al conductors. The resulting superconducting properties were comparative to those of Nb matrix conductors. The replacement of Nb matrix with Ta was very effective in suppressing flux jumps even at 4.2 K.