Study on the High Temperature Heat Treatment Process Optimization of Different Sizes High Jc Nb₃Sn Wire Produced by WST

The heat treatment process plays a central role in optimizing the critical current density of Nb <tex-math notation="LaTeX">₃</tex-math> Sn wire. Increasing the critical current density of Nb <tex-math notation="LaTeX">₃</tex-math> Sn wire, reducing the use amount of wire in magnets and reducing the price are important ways to promote the industrialization and mass application of Nb <tex-math notation="LaTeX">₃</tex-math> Sn wire. The Nb <tex-math notation="LaTeX">₃</tex-math> Sn microstructure state in the wire and an even distribution of Ti are critical factors for enhancing the current density of the wire. The grain size of the Nb <tex-math notation="LaTeX">₃</tex-math> Sn wire increases with the rise in heat treatment temperature. Therefore, the optimum temperature should be the lowest that ensures the full reaction/diffusion of each element.So the optimum third plateau heat treatment process of different size high Jc Nb <tex-math notation="LaTeX">₃</tex-math> Sn wire is: (1) the third plateau of outer diameter 0.82 mm wire is 640 °C, and the holding time is 50 h; (2) the third plateau of outer diameter 0.99 mm wire is 665 °C, and the holding time is 50 h; (3) the third plateau of outer diameter 1.30 mm wire is 665 °C, and the holding time is 80 h. The average critical current density of the wire, measured at 12 T and 4.22 K, has been increased from 2500 A/mm 2 to 2600 A/mm 2 .