Study On The Phase Formation Process And Superconducting Properties Of Ti And Ta Doped Nb₃Al Wires Fabricated By Rapid Heating,Quenching And Transformation Process

In this paper,Ta and Ti-doped Nb₃Al were subjected to rapid thermal quenching transformation（RHQT）heat treatment respectively to explore the phase formation process and superconducting properties of Ti and Ta-doped Nb3Al wires.The phase,microstructure,composition and superconducting properties of(Nb_1-xTa_x)₃Al and(Nb_1-xTi_x)₃Al（x=0.03,0.1）wires were compared and analyzed.In the Ta-doped Nb₃Al samples,with the increase of RHQ energy density,the metallography shows that the voids in the wire gradually change from irregular to round,the wire is fully reacted,and the content of bcc phase also increases gradually.After reaching a sufficiently high RHQ temperature,all Ta-doped samples can obtain bcc phase after RHQ and transform into Nb₃Al A15 phase after subsequent low temperature annealing.The samples exhibit Al-rich and Al-poor microstructures with Nb content above 70%.The Al content distribution of the 5at%Ta and 10at%Ta samples is wider,and theΔT_c of the samples is also wider.Ta doping reduces the T_c of the sample,and the greater the doping amount,the more the decrease.1%Ta has the highest critical current density J_c and irreversible field,the pinning mechanism conforms to the surface pinning mechanism,and the pinning center may be mainly stacking fault.With the change of RHQ conditions,the Ti-doped samples showed similar metallographic and microstructure as Ta-doped samples,and the samples with the same fully reacted had better superconducting properties.The(Nb_0.97Ti_0.03)₃Al wire with an energy density of 13.6 J/mm³ has a narrower superconducting transition width and has the highest critical current density J_c.The T_c of the(Nb_0.9Ti_0.1)₃Al wire is seriously decreased,which may be due to the excessive amount of Ti doping.Combined with the above results,the phase formation process and superconducting properties of Ti and Ta doped Nb₃Al superconducting wires were systematically analyzed.The wires after RHQ treatment all formed bcc phase,and the microstructure was Al-poor and Al-rich alternately.After low temperature annealing,all the wires were transformed into the A15phase,and the microstructure was the same as that of the quenched samples.When the doping amount is 3at%,the composition of the Ti and Ta doped Nb₃Al samples is close to the stoichiometric composition,but the Nb content of the 10at%Ti doped sample is constant at67at%,while the Al+Ta content of the 10at%Ta doped sample is always 25at%.Compared with the Ta-added samples,both micro-XRD and slow-scan XRD show that the mesoplanar spacing of the Ti-doped samples is smaller.The superconducting properties of 3at%Ti and Ta-doped Nb₃Al wires are comparable and far superior to the samples with 10at%,including critical temperature（T_c）,critical current density（J_c）,and irreversible field(B_irr).The 10at%Ta doped sample has higher T_c,but itsΔT_c is wider and J_c is poorer.