Preparation Of Single Core Nb₃Al Superconducting Wires By Rapid Heating And Quenching

In contrast to commercially available Nb₃Sn,Nb₃Al not only has higher critical transition temperature（T_c）and upper critical magnetic field(H_c2),but also possesses extremely critical current density（J_c）and excellent strain tolerance in high fields,as well as similar radiation sensibility like Nb₃Sn,so it has been considered as a potential alternative to Nb₃Sn for high-field applications,especially applied at magnetic fields much higher than25 Tesla and under extreme mechanical and irradiation conditions,such as nuclear fusion superconducting magnetic systems for the International Thermonuclear Experimental Reactor（ITER）,high-energy particle accelerators,gigahertz class nuclear-magnetic-resonance（NMR）analysis,and so on.Among the many preparation approaches of Nb₃Al,the rapidly heating and quenching is a relatively mature and practical method.From the perspective of practical application,this paper aims to explore a kind of low-cost,easy-to-process,high-performance single-core Nb₃Al superconducting wire,which is expected to be commercially manufactured.We made use of self-development RHQ device to complete the heat-treatment of the hundred-meter Nb/Al precursor wires,subjected to following annealing condition of 800℃/10h to realize the superconducting transition.Based on the modification of the RHQ device,the effects of a series of heating current values on the superconducting properties and microstructure of the Nb₃Al wires were explored,and a current platform interval（270A-275A）was found,which can make the quenched precursor wires have a certain plasticity and toughness.However,it is regrettable that the radius of the Nb center reinforcement rod of the precursor wires is not big enough,resulting in the wire can not run steadily and continuously under the large current.In the experiment,only a short sample with certain processing performance is obtained,its length is about 30cm.It is worth emphasizing that among all the samples,the sample with a heating current of 315A had the best superconductivity,the critical initial transition temperature（T_c）is 17.5K and the critical current density（J_c）was still as high as 4.7×10⁵A/cm² at 10K and a applied magnetic field of 7T.On the basis of a large number of experiments,I think that if we further optimize the preparation process of the precursor wires,we can realize the stable and continuous running of the wire at high current,and at the same time guarantee the good performance of the Nb₃Al superconducting wires.The concrete measures include reducing the proportion of Nb in Nb/Al composite layer,reducting the thickness of Nb foil and Al foil,making sure that the diffusion distance between Nb foil and Al foil is small enough（<0.1um）during winding.The most important thing is to increase the radius of Nb center reinforcement rod.Once the one-off RHQ treatment of hundred-meter precursor wires can be realized,and the quenched wires have excellent cold-working performance,which mainly reflected in possessing the ability to coil and magnet,it will greatly promote the commercial production and application of Nb₃Al superconducting wires.