Microstructures of TiAl joints brazed with CoFe-based and Fe-based high-temperature filler metals

CoFe-based and Fe-based high-temperature filler metals were studied for the control of the excessive reaction between filler metal and TiAl base metal at high brazing temperatures. The wett-ability of two filler metals on TiAl was studied at 1100°C/10 min and 1200°C/10 min, and the vacuum brazing experiment was carried out at 1180°C for 5min. The results showed that the contact angles of the two kinds of filler metals were about 30° at 1200°C/10 min. The interfacial reactions of the two filler metals with TiAl were not as strong as that of the traditional Ni-based filler metal. Main microstructures of the joint brazed with CoFe-based filler metal were Ti3Al, TiAl, silicide and (Ti, Cr)-B phase. Furthermore, a narrow Cr-rich solid solution zone (about 10 μm) was formed in the central part of the joint. The similar microstructures were formed for the joint brazed with Fe-based filler metal. But there is also a difference, for the joint brazed with Fe-based filler metal, a wider residual filler metal zone (about 40 μm) was formed in its central part, and the main phase was identified to be Fe-rich solid solution. TiB and TiB2 phases were formed near the residual filler metal zone, and the amount of borides was much more than that of CoFe-based filler metal.