The microstructural observation of brazing Ti–6Al–4V and TZM using the BAg-8 braze alloy

Abstract

Microstructural evolution of the brazed Ti–6Al–4V and TZM joints using the BAg-8 braze alloy have been evaluated in this study. According to the dynamic sessile drop test, the molten braze alloy can effectively wet Ti–6Al–4V at 850 °C. In contrast, the TZM substrate cannot be effectively wetted by the molten braze below 900 °C. The microstructure of an infrared brazed specimen (800 °C, 60 s) mainly consists of eutectic Ag–Cu, with a reaction layer (Ti 3Cu 4) approximately 2 μm thick. The interfacial reaction is more pronounced in a specimen furnace brazed at 800 °C for 600 s. Both TiCu and Ti 3Cu 4 are observed at the interface with the thickness of about 10 μm. In specimens furnace brazed at 850 °C, the reaction layer is mainly comprised of TiCu. The application of the infrared brazing cannot completely prevent the formation of interfacial reaction layer(s), but it provides an effective way to inhibit the growth of intermetallics at the interface between the braze alloy and substrate. Additionally, the dissolution of the substrates into the molten braze alloy during infrared brazing is significantly decreased due to its rapid thermal cycle.