Eutectic microstructure and its effect on electrical and magnetic properties of V-Ti-Si alloy superconductors

Abstract

The $\beta$-V${}_{1-x}$Ti${}_x$ alloys are promising superconductors for high field applications. Precipitating secondary phases without altering the composition of $\beta$-V-Ti binary phase can improve the critical current density (J${}_C$). Here we show that adding silicon generates eutectic microstructure in the V_0.60Ti_0.40 alloy, consisting of $\beta$-V-Ti and Ti${}_5$Si${}_3$ phases. Annealing stabilizes the two-phase microstructure. In comparison with the as-cast alloys, the annealed alloys have lower electrical resistivity for compositions lower than the eutectic composition (15 at.% Si). The superconducting transition temperature (T${}_C$) reduces slightly for the as-cast alloys but increases upon annealing. The J${}_C$ of the V_0.60Ti_0.40 alloy improved by the addition of Si and is further improved when the alloys are annealed. Analysis of the field dependence of pinning force density (F${}_P$) suggests that the large amount of grain/cell boundaries and the boundaries of phases with different superconducting properties in the V-Ti-Si alloys are effective in pinning the flux lines.