Single-Lap Shear Testing of a Boron-Free Cu–Mn–Ni Filler Metal for Brazing IN625

In transient liquid-phase bonding (TLPB) of Ni-based superalloys, B is often used as the filler metal melting point depressant. However, this can result in the formation of brittle borides and reduced mechanical properties. The current authors recently developed a B-free filler metal using Cu and Mn as melting point depressants. In this paper, single-lap shear tests were used to compare the mechanical properties of this B-free filler metal (Ni30) to a commonly used B-containing filler (BNi-2) when brazing IN625 base metal. Brazing of both fillers resulted in an isothermally solidified braze gap and athermally solidified fillets at each end of the joint. In tensile testing, failure in all specimens originated in the fillet where stresses were highest. However, failure in the Ni30 specimens propagated along the filler to base metal interface in a shear or peeling mode. The BNi-2 specimens had a thicker diffusionally affected zone (50 to 70 vs < 10 μm in Ni30) which reduced the effective thickness of the base metal and caused failure to occur through this thickness in a tensile mode. The resulting tensile stresses at failure were ~ 14 pct higher in the B-free Ni30 specimens compared to those with BNi-2 filler.