Phase formation and enhanced performance of Nb3Al prepared by spark plasma sintering and subsequent annealing

Abstract

Although the Nb3Al wire prepared by the rapid heating and quenching (RHQ) technique has achieved excellent superconducting critical current density (Jc), various new preparation techniques have still been continuously tried to improve its performance. In this paper, the phase formation and superconducting properties of Nb3Al prepared with spark plasma sintering (SPS) was studied. It is found that the SPS in the temperature range of 1200–1400 °C can quickly produce high-density, nano-structured Nb3Al superconductor, which has a transition temperature around 16 K. Due to its tight and clean grain connection, the sample shows a high-performance current-carrying capacity in self-field. After post-annealing, the flux pinning force and the superconducting performance are significantly improved. The study clarified that the phase formation mechanism of the SPSed Nb3Al is similar to that directly formed from high temperature liquid phase rather than the transformation from bcc phase to A15 phase. The high temperature liquid phase may originate from the local high temperature induced by the plasma heating in the early stage of SPS process. Such a unique phase formation mechanism results in very few structural defects existing inside the sample. The results of this study suggest that chemical doping or other means which can introduce high density structure defects in Nb3Al should be considered to further improve the in-field Jc for the SPSed Nb3Al.