Bonding mechanism between alumina and niobium

Abstract

Diffusion couples of Al₂O₃ single-crystal, sapphire, and Nb polycrystal were heat-treated in the temperature range 1873 to 2073 K under pressure in the range 3 to 15.2 MN m⁻² for various times up to 3.6×10³ sec. Tensile testing at various temperatures up to 1873 K in a vacuum of about 10⁻³ Pa, Knoop hardness testing at room temperature, optical microscopy, scanning electron microscopy, transmission electron microscopy, and electron-probe X-ray microanalysis studies were carried out on the specimens. From the results, it was concluded that the fairly high bond strength of a Al₂O₃-Nb interface might be attributed to the formation of a thin NbO _x layer, which had grown epitaxially on the Al₂O₃ surface. Lattice matching between Al₂O₃ and NbO _x phases was also considered.