Reaction layers and mechanisms for a Ti-activated braze on sapphire

A study was conducted to understand the wetting phenomena observed in brazing of a Ti-containing active filler metal on sapphire substrates. The goal of the study was to understand the interfacial reactions that permit wetting of commercial Ag-Cu-Ti active filler metal to pure alumina, despite the lower thermodynamic stability of TiO^sub 2^ relative to Al^sub 2^O^sub 3^. Based upon transmission electron microscope, electron microprobe, and Auger analyses, it is proposed that two coupled reactions and diffusion of reactants take place. The oxides TiO, Ti^sub 2^O, and Cu^sub 3^Ti^sub 3^O were observed at the braze/ceramic interface. It is suggested that the complex oxide Cu^sub 3^Ti^sub 3^O grows at its interface with TiO, and the oxide TiO is produced by reaction of Ti and sapphire and is subsequently consumed at its interface with Cu^sub 3^Ti^sub 3^O. It is also suggested that Ti^sub 2^O forms from Ti and TiO while cooling from the brazing cycle. [PUBLICATION ABSTRACT]