The influence of the purity and thickness of niobium foils on its mechanical properties

The content of contaminants, microstructures, surface condition, electrical resistivity, and mechanical properties of niobium foils and bands (13-1000 μm thick) after cold working (90-99.9%), surface etching, and heat treatment under vacuum (0.001 Pa at 700-1200 0C for 1-5 hrs) are studied. The effect of the previous working and different environmental conditions including initial and acquired surface contamination with oxygen, carbon, nitrogen, and iron increases noticeably with the rise of the working degree and decrease of the foil thickness. The mechanical properties of foils and bands (>= 100 μm) practically don't differ from massive standard samples. At the foil thickness of <= 40 μm the dimensional effects and the influence of the surface layer are especially noticeably. The optimal combination of the whole complex of surface and volume properties at the minimum dimensional effects is observed on the 50 μm thick foil. The improvement of foil properties can be achieved due to etching its surface layer up to the depth not less than 4 μm (on each side) after the cold working and following annealing at 1000-1100 0C (1-3 hrs). (author)