Interfacial microstructure and mechanical properties of TiAl alloy/TC4 titanium alloy joints diffusion bonded with CoCuFeNiTiV0.6 high entropy alloy interlayer

In this paper, a novel CoCuFeNiTiV 0.6 high entropy alloy interlayer was used for vacuum diffusion bonding of TiAl alloy and TC4 titanium alloy. The effects of bonding temperature and pressure on the interfacial microstructure, element diffusion behavior and mechanical properties of the joint were investigated. According to the microscopic morphological characteristics of the joint, it is divided into four zones. Zone I and zone III are the TiAl side interface diffusion layer and the TC4 interface diffusion layer, respectively. Zone II is the bonded high-entropy interlayer, and zone IV is the diffusion region of the TC4 substrate. Three diffusion layers of B2 phase, Al(Cu, Ni)Ti and Al(Co, Ni) 2 Ti phase were formed in zone I, while two diffusion layers of Ti-rich IMC and Ti 2 Ni phase were formed in zone III. With the increase of bonding temperature and pressure, the different diffusion layers on the TiAl side interface gradually thickened, and the β-Ti region on the TC4 side became wider and the Widmanstätten microstructure increased. The mechanical properties of the joints were evaluated by nanoindentation and shear tests. The hardness and elastic modulus at the TiAl side interface are up to 8.12 GPa and 158 Gpa, respectively, which is easy to cause stress concentration. The maximum shear strength reached 96.2 MPa bonded for 60 min at 960 ℃ under 1.7 MPa. The fracture location in the joint generally occurs at the interface of the Al(Cu, Ni)Ti layer/Al(Co, Ni) 2 Ti layer/HEA interlayer, and the fracture is mainly characterized by brittleness. • Diffusion bonding of TiAl alloys to TC4 titanium alloys was performed using high-entropy alloys as interlayers. • The interlayer alloy can possess the benefits of both a ductile FCC phase along with the strength increment imparted by the BCC constituent phases • The mechanism of the effect of high entropy effect and sluggish diffusion effect on the diffusion bonding process is discussed. • Dynamic recrystallization and atomic interdiffusion at the interlayer interface are key factors for the formation of the joint microstructure. • The growth rate of the reaction layer with higher growth activation energy is greater than that of the reaction layer with lower growth activation energy. • With the increase of bonding temperature and pressure, the shear strength of the joint increases, and the shear strength of the joint reaches the maximum value of 96.2 Mpa.