Infrared brazing of TiAl intermetallic using pure silver

Abstract

Titanium aluminides have been extensively studied due to their high specific strength and fairly good corrosion as well as oxidation resistance. The development of joining process always plays a crucial role in application of these alloys. Infrared vacuum brazing is a novel technique featured with a rapid thermal cycle. The present work reports the successful infrared brazing of TiAl using pure Ag as brazing filler metal. The transient microstructural evolution of the joint as well as its bonding strength is extensively evaluated. The infrared brazed joint is primarily comprised of Ag-rich phase solid solution with Ti and Al. There are three phases in the reaction layer, including Ti(Al,Ag), Ti 3(Al,Ag) and Ag-rich. The formation of Ti 3Al in the reaction layer can be attributed to the dissolution of TiAl substrate into the Ag-rich molten braze. It is found that the Ag-rich phase dissolves much more Al than Ti. The consumption of Al can result in local enrichment of Ti atoms, so Ti 3(Al,Ag) phase is formed. The use of pure Ag filler metal demonstrates excellent bonding strength of the joint. All specimens brazed at 1050 °C were fractured at TiAl substrate. Specimens brazed at 1100 °C above 60 s demonstrate shear strength up to 385 MPa. However, the fracture location changes from TiAl substrate into the brazement. The fracture location is either at the Ag-rich matrix or at the interface between the reaction layer and Ag-rich matrix