Interfacial Reactions between Cu-Zr filler metal and alumina and kinetics of reaction layer growth

The interfacial reactions and kinetics of the reaction layer growth in Cu-Zr/A1₂O₃ system were investigated and compared with those in Cu-Ti/Al₂O₃ system. Therrnodynamic analysis showed that the interfacial reaction can proceed until the activity of aluminum in the Cu-5 at.% Zr filler metal reaches about 0.27 at 1373 K. Growth of reaction layer, ZrO₂, was controlled by the diffusion of oxygen through ZrO₂ layer. The activation energy for ZrO₂ growth was 126 kJ/mol. Instead of using a complex redox reaction, a simple oxidation model between reactive metal and oxygen was found to adequately describe the reaction layers growth in ceramic/metal systems. The parabolic rate constant could be expressed in terms of oxygen vacancy concentration at the reactive metal/reactive metal oxide interface. The slower growth of TiO, in comparison with ZrO₂, can be rationalized using the parabolic rate constant. The lower diffusion coefficient of oxygen vacancy and a less negative free energy change of TiO formation have a dominant effect over the higher oxygen vacancy concentration at the Ti/TiO interface which resulted in slower TiO growth.