Induction brazing of Ti-6Al-4V alloy with amorphous 25Ti-25Zr-50Cu brazing filler metal

Abstract

Ti-6Al-4V alloy was induction brazed with 25Ti-25Zr-50Cu amorphous filler metal using argon as a shielding gas. The brazing cycles were rather short: RF inductor power was supplied for only 40–60 s. The tensile strength and ductility of the brazed joint are at the level of that of Ti-6Al-4V base metal. According to SEM/EDAX and STEM phase analysis, two main joint microstructures are observed: either a very fine lamellar/cellular eutectoid consisting of mixture of α-Ti + γ-(Ti,Zr) 2Cu tetragonal MoSi 2 type phase or martensitic α′-Ti with dispersed γ-phase. The final copper concentration in the joint area is considered one of the critical parameters for joint microstructure formation. The optimal, eutectoidal microstructure characteristic of a ductile joint is obtained under brazing conditions that should result in average copper joint concentration within the 10–12 wt.% range. It is also found that the postbrazing natural cooling rate of 12.5 mm diameter rod samples is sufficient to suppress the formation of undesirable brittle λ-Cu 2TiZr Laves phase appearing in vacuum furnace brazing due to inherently low cooling rates. A variety of metallurgical paths along which base and filler metal may interact is proposed, explaining the mechanisms of formation of various braze microstructures and mechanical properties related to them. From the practical point of view, it is proved that induction brazing of compatible samples located in a simple close chamber may be carried out as an effective and inexpensive process.