Interfacial morphologies between alumina and silver-copper-titanium alloy

Joints of high-purity Al2O3 were made with a Ag57Cu38Ti5 alloy by vacuum brazing at 800 °C and 900 °C for 30 min. The microstructures at the interface between the ceramic and the alloy were examined in cross-section by scanning electron microscope (SEM) and on different planes parallel to the interface layer-by-layer by optical microscope (OM), respectively. The chemical composition of the reaction product was also analysed by energy dispersive X-ray (EDX). A thin reaction layer about 1.0 μm thick was formed on the Al2O3 surface at a temperature of 800 °C. This layer had three kinds of morphologies and they were identified as Ag, Cu2Ti4O and AlTi, respectively. According to SEM and OM results, there were two distinct layers 4.0 μm thick interfacial reaction layer for sample heated at 900 °C, one layer in the vicinity of the ceramic consisting mainly of Ti2O and TiO and the other layer near the alloy was CuTi2. A transition layer structure composed of Al2O3/Ti2O + TiO/Ti2O + TiO + CuTi2/CuTi2/Ag–Cu was formed at the interface. The Al concentration at the interface was relatively high and confirmed that the reduction of Al2O3 by Ti occurred, which was consistent with the result of a thermodynamic analysis.