Infrared joining strength and interfacial microstructures of Ti-48Al-2Nb-2Cr intermetallics using Ti-15Cu-15Ni foil

Infrared joining of Ti-48Al-2Nb-2Cr using Ti-15Cu-15Ni (wt%) foil as brazing filler metal was investigated at the temperature range of 1100 similar to 1200 degrees C for 30 similar to 60 s in a flowing argon environment. The compressive tests show three types of fracture morphologies in which type I fails at the joint interface, but types II and III are fractured in the base-metal with the crack direction parallel to and perpendicular to the loading axis, respectively. Most of joined specimens were fractured through the base metal indicating that the infrared joined interface has relatively good joint strength. The compressive strength of type I specimen is about 319-322 MPa. Experimental results show that the shorter the real hording time or the higher the joining temperature, the larger the strength variation will be. The observed interfacial microstructures of Ti-48Al-2Nb-2Cr joint interfaces indicate that seven characteristic zones can be distinguished in the joint interfaces and each characteristic structure corresponds to one or more stable phases at T-w temperature. The observed microstructures and their evolutions of each zone are explained in detail in this study. The major difference between joint interfaces of Ti-48Al-2Nb-2Cr and Ti50Al50 alloys takes place on the base-metal interface zone and the columnar two-phase zone. The existence of Nb and Cr atoms in Ti-48Al-2Nb-2Cr alloy also has some influences on the microstructural evolution of the columnar two-phase zone and the continuous alpha(2)-layer. (C) 1998 Elsevier Science Ltd. All rights reserved.