To achieve both high purity in the ingot to ensure a residual resistivity ratio (RRR > 300) meeting the requirements for superconductivity, and fine, uniform grain size to facilitate subsequent plastic forming and obtain pure niobium products with uniform microstructure and excellent mechanical properties, this application, through systematic research and experimental exploration, has discovered that adding trace amounts of yttrium during the smelting process in a vacuum electron beam cold hearth furnace can control the as-cast grain size and limit impurity content, ensuring that the final pure niobium product meets the required RRR value, thus achieving a balance between these two performance aspects.
In some embodiments, the yttrium element is yttrium powder dissolved in an organic solvent. The purpose of this invention is to solve the problem that adding yttrium to refine the microstructure of pure Nb alloy ingots results in insufficient refinement if the amount added is too small, while excessive addition leads to a decrease in the RRR value.
Alternatively, by surrounding the pure niobium electrode with multiple turns of yttrium wire, the resulting pure niobium ingot material exhibits fine grains, good microstructure uniformity, and an RRR value (> 300).
If the drying temperature is too low, the solvent evaporates slowly; if the drying temperature is too high, the yttrium distribution on the niobium electrode is uneven. Therefore, in some embodiments, the drying conditions are 60–65°C for 25–30 minutes to ensure uniform yttrium distribution on the niobium electrode while improving drying efficiency.
Pure niobium ingots are characterized by fine grains, good microstructure uniformity, and a high residual resistivity ratio (RRR > 300), yielding uniform equiaxed ingots with an average grain size of 5–15 mm. By adding 0.01–0.06 wt% yttrium during the melting process, and maintaining the solution in the cooling bed for 10–600 seconds with continuous stirring by the electron beam during electron beam melting, followed by pouring into a crystallizer, an equiaxed ingot with a cast grain size of 4–10 mm can be obtained.
The terminology used herein is for describing particular embodiments only and is not intended to limit the exemplary embodiments according to this application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. Furthermore, it should be understood that when the terms “comprising” and/or “including” are used in this specification, they indicate the presence of features, steps, operations, devices, components, and/or combinations thereof.
