Microstructural characterization of interfacial reaction products between alumina and braze alloy

Abstract

The Al₂O₃/STS304, Al₂O₃/Cu and Al₂O₃/Al₂O₃ joints were brazed in vacuum with three types of Cu-Ag-Ti brazing filler metals at 1193 K for 1.2 ks. The effects of adherend metals on the microstructure and microchemistry of reaction products formed at the Al₂O₃/filler metal interface have been investigated. The reaction products of A₂O₃/STS304 joints showed a layered structure consisting of TiO (monoclinic, a ₀=0.585 nm, b ₀=0.934 nm, c ₀=0.414 nm), Cu₂Ti₄O (cubic, a ₀=1.149 nm) and Fe₂Ti₄O (cubic, a ₀=1.1297 nm). The TiO compound is a nonstoichiometric titanium monoxide with composition range of TiO_0.9 to TiO_1.1. Cu₂Ti₄O and Fe₂Ti₄O compounds can be considered as (Cu, Fe)₂Ti₄O because both of them have nearly the same crystal structure and lattice constants. The reaction products of Al₂O₃/Cu and Al₂O₃/Al₂O₃ joints also showed a layered structure consisting of TiO and Cu₂Ti₄O. The TiO compound was formed by redox reaction between Al₂O₃ and segregated titanium, whereas Cu₂Ti₄O and Fe₂Ti₄O compounds formed by solid-state reaction between TiO and copper from the brazing alloy and iron from the adherend metals, respectively.