Transient liquid phase bonding of a Hf bearing single crystal nickel aluminide to MM247 superalloy

An investigation of transient liquid phase bonding of single crystal NiAl t o a conventional polycrystalline nickel base superalloy MM247 is presented here. The NiAl substrate material employed was cast single crystal NiAl (B2 compound beta phase) with 1.5 at.-% hafnium (Hf) as an alloying element. T he interlayers employed in the bonds were 50 mu m thick pure copper foils. Based an investigations employing transmission electron microscopy and scan ning electron microscopy with energy dispersive X-ray spectrometry: the mic rostructural changes in the joint region and the adjacent substrates were e xamined as a function of bonding time at a temperature of 1150 degrees C. T he results indicated that hafnium as an alloying element in single crystal NiAl had a strong effect on the microstructure of joints. In particular; at tention is focused on the formation of Hf bearing phases and the suppressio n of sigma phase precipitation during bonding. MST/3995.