NbTi superconducting composite with high critical current density

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Abstract
In order to make NbTi50/Cu superconducting composite obtain high critical current density, we have studied carefully the melting method for NbTi50 alloy and the effect of cold work and heat treatment on critical current density. The results show that the ingots obtained through vacuum arc and a vacuum skull furnace melting can be used to fabricate NbTi superconducting composite with high critical current density. Cold work and heat treatment are the important factors which effect the critical current density of NbTi50/Cu superconducting composite. The restarts show that intermediate ageing treatments have improved the critical current density of NbTiSO/Cu composite. If a sample is treated intermediately for several times before final ageing, the Jc of the sample is much higher than that of the final aged sample of the same ageing time. As the intermediate ageing number is increased, the value of Jc (5T,4.2K) increased. It increased rapidly especially at the second and the third ageing. When the cold work between ageing treatments is increased, the value of Jc (5T, 4.2K) increased markedly. The heavier the cold work between ageing treatments is, the higher the Jc (5T, 4.2K) will be. Final deformation has further improved the critical current density of NbTi50/Cu composite in our range of experiment, Jc (5T, 4.2K) increased rapidly for the samples aged at 350°C and 385°C when the final deformation increased. The value of Jc (5T, 4.2K) comes up to 3.4 × 105A/cm2for the sample of the final deformation 90% after the last ageing at 385°C. In order to make NbTi50/Cu superconducting composite obtain high critical current density, cold work and heat treatment must be regulated and coordinated appropriately. We have chosen suitable heat treatment and cold work so that the highest critical current density has reached 3.9-4.14 × 105A/cm2(5T, 4.2K) for the optimum NbTi50/Cu multifilamentary composite.