EUROPEAN CONGRESS AND EXHIBITION ON ADVANCED MATERIALS AND PROCESSES - EUROMAT 2021

Brazing and active metal brazing are reported to be straightforward techniques to produce sound metal/ceramic joints. The performance of brazed joints is highly dependent on the microstructure developed at the interface. For instance, the use of Ag-Cu eutectic based fillers strongly limits the operating temperature of joints due the extensive formation of (Ag) at the central zones of the interfaces. Contrastingly, Ti based fillers do not present this issue, but require higher brazing temperatures and significant volume fractions of brittle phases are often reported at the interfaces. This highlights the importance of adequate brazing filler selection as well as of understanding and controlling the microstructure evolved at the brazing interfaces, which strongly influences the mechanical properties of joints and the service life of joined components.
This study evaluates the feasibility of brazing Ti6Al4V to ZrO2 using a Ag-Cu sputter-coated Ti brazing filler foil that prevents the extensive formation of (Ag) at the interface and enables brazing at lower temperatures than those required for joining with conventional Ti-based fillers. Brazing was conducted in vacuum, at 900, 950 and 980 ℃ for 30 min. Cross sections of joints were analysed by scanning electron microscopy and energy dispersive X-ray spectroscopy. Multilayered interfaces consisting of (Ti) and Ti-Ag intermetallics were obtained for all brazing temperatures. For brazing at 900 ℃, the central zone of the interface, which is essentially composed of (Ti) and of lamellar constituent is delimited by two continuous TiAg layers. For the higher processing temperatures, these layers are not detected and Ti2Ag becomes the predominant intermetallic phase. As the brazing temperature is incremented, the residual porosity located near the ceramic sample tends to increase.