Formation of TiAl₃ and its reinforcing effect in TA15 alloy joint ultrasonically brazed with pure Al

In this work, TA15 joints reinforced in situ with TiAl₃ IMCs were successfully fabricated using pure Al filler by ultrasonic brazing. TA15 alloys were first wetted by pure Al with and without ultrasonication and then ultrasonically brazed. The wetting of Al to the TA15 alloy was realized by the formation of a TiAl₃ phase at the contacting interface. The complete wetting of the Al filler to the TA15 substrate was achieved at 20 min without ultrasonication. Ultrasonication significantly accelerated the wetting process, and the time required to achieve complete wetting was shortened to 10 s. During ultrasonic brazing, the formation of TiAl₃ in the joint mainly depended on the holding time. The content of the TiAl₃ phase increased from 35.2% to 77.2% as the holding time was increased from 5 min to 30 min. Joint strength increased with the amount of TiAl₃ in the joint. Ultrasonication for 10 s and a holding time of 30 min generated a joint filled with homogeneously distributed TiAl₃. The maximum shear strength of this joint was 140.6 MPa, which was 75% higher than that of pure Al. Failure crack propagated through the filler at short holding times and through the filler and TiAl₃ phase at prolonged holding times.