The microstructure and forming mechanism of diffusion brazing interface of TiAl alloy and 42CrMo

In this paper the structure and forming mechanism of reaction layer of TiAl/B-Ag72Cu/42CrMo joint of vacuum diffusion brazing at 870℃ were studied by metallographic microscope , scanning electron microscope, electron probe. The results showed that there is no intermetallic compound forming at the interface of the B-Ag72Cu/42CrMo, but Ti(Cu, Al)2 intermetallic compound forming at the interface of the TiAl/B-Ag72Cu. The forming and growth mechanism of intermetallic compound layer have been analyzed and divided into two stages. The elemental diffusion is the dominant factor of joint forming. The forming and growth of intermetallic compound layer is mainly composed of several processes as follows: melting of filler metal, preferential diffusion along grain boundary, isothermal solidification, columnar and mushroom shaped growth and longitudinal growth.