Microstructure of Alumina Brazed with a Silver‐Copper‐Titanium Alloy

Joints of high‐purity Al 2 O 3 were made with a 56Ag‐36Cu‐6Sn‐2Ti (wt%) experimental alloy by vacuum brazing at 900°C for 20 min. The microstructure at the ceramic‐metal interfaces was examined in cross‐sectional specimens of the joints, and phases formed by reaction between the braze filler metal and the Al 2 O 3 were analyzed for composition and crystal structure in a transmission electron microscope. A 0.1‐ to 0.2‐μm‐thick layer formed directly on the Al 2 O 3 surface. This layer was Ti‐rich, had the face‐centered‐cubic crystal structure with a lattice parameter of 0.423 nm, and was identified as oxygen‐deficient γ‐TiO. The second reaction layer was ∼3 μm thick, and it separated the TiO layer from the metallic phases of the braze filler metal. The structure of this layer, as determined by electron diffraction, was diamond cubic of the space group Fd3m , with a lattice parameter of 1.137 nm. The combination of microanalysis and diffraction data confirmed that this phase was Ti 3 (Cu 0.76 Al 0.18 Sn 0.06 ) 3 O and indicated that it can be classified as an n phase.