Laser powder bed fusion of NbTi low-temperature superconductors

This study investigates the superconducting properties of additive manufactured in-situ NbTi alloy using laser powder bed fusion. Laser parameters were optimised for a maximum microstructural density and lowest Nb segregation fraction. These characters have been achieved at the sample built with an energy density of 3.33 J/mm 2 , where it shows a density value of 6.12 g/cm 3 , undissolved Nb fraction of 0.05 %, and randomly distributed equiaxed grains with an average size of 10–20 μm. Post-processing of the as-fabricated (AF) sample was explored as a route to collapse residual porosity and dissolve residual segregated Nb particles using hot isostatic pressing (HIP) and heat treatment, respectively. HIPing resulted in a decrease of the undissolved Nb particle fraction to 0.035 %. Heat treatment at 1250 °C for 24 h, followed by aging at 400 °C for 2 h, was found to result in the complete dissolution of Nb particles and precipitation of the ɑ-Ti phase that works as pinning centres to increase the superconducting properties. The grain size increased in both post-processes to 400–500 μm. Electrical and magnetic properties were also measured for the AF, HIP and heat-treated samples. The thermal variation of electrical resistivity showed a critical temperature ( T c ) range of 9.8–9.0 K, 9.6–9.1 K and 9.9–8.8 K for the AF, HIP, and heat-treated samples, respectively, which were close to the values obtained from magnetic measurements. The critical current density ( J c ) was calculated using Bean’s model employing the magnetic hysteresis loops. The AF condition showed a negligible value of J c (5 × 10 −3 kA/mm 2 ), which improved to 0.28 kA/mm 2 and 2.65 kA/mm 2 for the HIPed, heat treated conditions, respectively (at 4.2 K, 5 T). Mechanical tensile testing was performed for the heat-treated sample to ensure both mechanical and superconducting properties would achieve the required performance, where achieves ultimate tensile strength value of 930 MPa, with 8 % elongation. • In-situ alloying approach is applicable to generate Nb 53 Ti 47 alloy using laser powder bed fusion. • Isotropic microstructure is achieved in the additive manufactured condition. • Heat treatment is essential to dissolve the segregated Nb particles. • Precipitation heat treatment provides superconductivity by generating ɑ-Ti phase.