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.

In this study, intermetallic TiAl and steel 40Cr are diffusion bonded successfully by using a composite barrien layer Ti/V/Cu. 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. 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.

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 development of thermal stress during the diffusion bonding of Al2O3 ceramic to Al is analyzed by the finite-element analysis using MARC/MENTAL code. Prior to diffusion bonding, a Cu layer of 0.2mm in thickness is sintered on the ceramic. The results show that shear stress concentration occurs in the ceramic near the corner of Al2O3/Cu interface, and tensile stress concentration occurs near the corners of Al2O3 outer surface during cooling from bonding temperature to room temperature. After tensile stress concentration on the Al2O3 undersurface rises to a certain value, ceramic deforms gradually, resulting in stress beginning to relax. The stress relaxation originates in the stress concentration region of Al2O3 outer surface.

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.