Joining of TiAl alloy using novel Ag-Cu sputtered coated Ti brazing filler

The aim of this study is to evaluate the potential use of titanium foil coated with sputtered silver and copper films as a novel brazing filler for joining TiAl alloys. For this purpose, a detailed microstructural characterization of the resulting brazing interfaces was carried out. The development of brazing fillers that allow the joining of TiAl alloys without compromising the service temperature is a fruitful prospect. Brazing experiments were performed in a vacuum at 900, 950, and 980 degrees C, with a dwell time of 30 min. Microstructural characterization reveals that brazing joints can be obtained successfully at 950 and 980 degrees C. The interface consists of a large central region of alpha-Ti with an amount of Al and Ti-Ag compound and thin layers, mainly composed of intermetallic compounds, formed close to the base material. A novel brazing filler consisting of Ti foil coated with sputtered Ag and Cu films inhibits the extensive formation of soft (Ag) zones or coarse brittle Ti-Al-(Cu,Ni) particles. Hence, the need for post-brazing heat treatments for the joining of TiAl alloys was avoided.
This research is sponsored by FEDER funds through the program COMPETE-Programa Operacional Factores de Competitividadeand by national funds through FCT-Fundacao para a Ciencia e a Tecnologia, under the project PEst-C/EME/UI0285/2013. The authors are grateful to CEMUP-Centro de Materiais da Universidade do Porto for expert assistance with SEM and EDS.