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

Abstract

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.