Nanoscopic analysis of a Ag-Cu-Ti/sapphire brazed interface

Transmission electron microscopy was employed to investigate the detailed nanoscopic structure of a sapphire/Ag-Cu-Ti brazed interface. Sapphire substrates with various plane directions were brazed by a Ag-Cu-Ti alloy, and their cross sections were investigated in terms of interface structure and orientation relationships between phases. The reaction phases formed during brazing were identified by nano-probe compositional analysis and electron diffraction. The typical interface structure was Ag-Cu eutectoid/Ti₃Cu₃O (1-2-μm-thick layer)/TiO (10-50-nm-thick layer)/sapphire, which generally existed at the interface in all the samples investigated. Al was present as solute in the reaction phases. However, the interface structure was multiple, which can be due to the local deviation of titanium and oxygen activities. In some regions where TiO was formed as discrete precipitation, an atomically-flat Ti₃Cu₃O/sapphire was present without TiO interlayer. Occasionally, a reaction phase without titanium concentration, Cu-Al-O, existed in contact with the sapphire substrate, which suggests a direct reaction between copper and sapphire.