Vacuum diffusion bonding of TiB2 cermet to TiAl-based alloys using Ni interlayer has been carried out at 1123-1323K for 0.6-3.6ks under 80MPa. The effects of joining parameters on the microstructure of the joints and mechanical properties was investigated. The results showed that a TiAlNi2 intermetallic layer and two Ti, Al, Ni solid solution layers were formed at the interface of Ni/TiAl. The shear strength was 110MPa with bonding temperature T=1223K, bonding time t=1.8ks and bonding pressure P=80MPa.

Vacuum brazing of TiAl-based alloy to 40Cr steel has been carried out at 1173K for 0.5-40min using Ag-Cu-Ti filler metal. The microstructural analyses indicate that three reaction products, Ti(Cu,Al)2, Ag(s.s.) and TiC, are present in the brazing seam, and the interface structure of the brazed joint is TiAl/Ti(Cu,Al)2 +Ag(s.s.)/Ag(s.s.)+Ti(Cu,Al)2/TiC/40Cr. The experimental results show that the shear strength of the brazed TiAl/40Cr joints decreases as the brazing time increases, and it is up to 175MPa when the joint is brazed at 1173K for less than 2min.

The brazing of TiC cermet to cast iron was carried out at 1223K for 5-30min using Ag-Cu-Zn filler metal. Formation phase, interface structure and shear strength of the joint were investigated. The results show: There occur three formation phases: Cu-base solid solution, FeNi and Ag-base solid solution in TiC cermet/cast iron joint. The amounts of Cu-base solid solution and FeNi increase and the amount of Ag-base solid solution decreases as brazing time increasing. When brazing time is 20min, the highest shear strength of the joint is up to 292.0MPa and the interface structure of the joint can be expressed as TiC cermet/Cu-base solid solution + FeNi/Ag-base solid solution + a little Cu-base solid solution + a little FeNi/Cu-base solid solution + FeNi/cast iron.

In this study, intermetallic TiAl and steel 40Cr are diffusion bonded successfully by using a composite barrien layer Ti/V/Cu. The relationship of the bond parameters and tensile strength of the joints was discussed, and the optimum bond parameters were obtained. The reaction products and the interface structures of the joints were investigated by SEM, EPMA and XRD. In this case, a diphase Ti3Al+TiAl layer and a Ti solid solution which enhance the strength of the joint are obtained at the TiAl/Ti interface. Formation mechanism at the interface of TiAl/Ti was propounded. The whole reaction process can be divided into three stages. In the first stage, Ti (ss.Al) layer is formed at the interface TiAl/Ti40Cr. In the second stage, TiAl+ Ti3Al layer are formed adjacent to TiAl, in the mean, the continuous diffusion of Al atoms from TiAl to Ti gives occasion to the formation of Ti3Al. In the last stage, the thickness of each reaction layer increases with bonding time according to a parabolic law. The interface of TiAl/Ti/V/Cu/40Cr was free from intermetallic compounds and other brittle phases, and the strength of the joint was as high as 420MPa, very close to that of the TiAl base. This method gives a reliable bonding of intermetallic TiAl and steel 40Cr.

Through eliminating voids not affecting the primary bonding process, and incorporating interlayer and flexible base material, the interface geometry character and brief mathematics process was put forth. Through analyzing contact process of diffusion bonding, contact area model was settled. It can interpret the phenomenon of different interface areas taking on different strengths. In the course of physical contact, shear stresses serve an important function for the plastic deformation and the cohesion of interface voids.