Effect of Ti content on microstructure and properties of Cu/AgCuTi/Al2O3 brazed joints

Abstract

In this study, four groups of Ag-Cu-Ti brazing powder with different Ti contents of 2 wt%, 3 wt%, 3.75 wt% and 4 wt% were prepared by vacuum atomization, and then modulated into brazing pastes. Brazing between oxygen-free copper and alumina ceramics with the brazing pastes and the wettability experiments of the brazing pastes on alumina were done by vacuum brazing process at 880℃ for 30 min. Microstructures and wettability of both the braze alloy and joints were analyzed by scanning electron microscope, energy dispersive X-ray spectrometer and transmission electron microscope, and shear strength of the joints was tested by self-designed fixture. Based on thermodynamic calculation and kinetic analysis, the relationship between the products of the reactive layer and the change of Ti content was plotted to explore the reaction and wetting mechanism of AgCuTi braze alloy on alumina ceramics. The results show that the content of Ti in AgCuTi braze alloy is the main factor affecting the brazing performance and wettability of the braze alloy by affecting the products of AgCuTi/Al2O3 reaction layer. The reaction layer consists of TiO when the Ti content is 2 wt%, the reaction layer comprises of TiO and Ti3Cu3O when the Ti content is 3 wt%, the reaction layer is made up of Ti3O2 and Ti3Cu3O when the Ti content is 3.75 wt%, and the reaction layer consists entirely of Ti3Cu3O when the Ti content is 4.6 wt%. With the increase of the Ti content within the range of 2–4.6 wt%, the wettability of the braze alloy on the alumina ceramics improved, and the shear strength of the Cu/AgCuTi/Al2O3 joints increased.