A series of diffusion bonding tests are conducted on a high Nb containing TiAl alloy with full lamellar (FL) microstructure and the effect of interfacial recrystallization behavior on the shear strength is discussed. Microstructural observations reveal that bonding above 1 100 C and 30 MPa results in recrystallization at the bonding interface flanked by FL microstructure, thus promoting the interface migration and leading to a sound joint. Based on the present results, the nucleation mechanism of recrystallization at the bonding interface is studied. Shear testing results show that recrystallization at the bonded zone improves the bonding quality of the joints by changing the failure mode. The shear strength of the joints attains 400 MPa when bonding at 1 150 C/30 MPa/45 min and 1 100 C/40 MPa/45 min.

A series of diffusion bonding tests were conducted on high Nb containing TiAl alloy with duplex microstructure, the evolution of microstructure at bonding interface was investigated. Bonding process was performed by using vacuum hot press furnace at the temperature range from 850 to 1150°C with the pressure of 30MPa for 45min. The microstructure observation indicates that sound joint without unbounded area can be obtained when bonded above 950°C. Recrystallization happens in bonding interface when bonded at 1150°C and the recrystallized grain prior nucleated at bonding interface between the lamella colonies. Nucleation and growth of recrystallized grains promote migration of bonding interface and thus improve bonding quality. Besides, the post-bonding heat treatment (PBHT) was also performed to promote the evolution of bonding interface. The experimental results reveal that the bonding interface disappears after PBHT at 1135°Cfor 12h, and exhibits near gamma microstructure.

The solid-state diffusion bonding experiments of high Nb containing TiAl alloy were successfully carried out at 950°C under a uniaxial pressure of 30MPa for 45min, and the influence of different initial microstructures, such as initial forged microstructure (named duplex microstructure) with different grain sizes, near lamellar microstructure and full lamellar microstructure, on the interface of the bonding joints were investigated. And the microstructure characterization of interfaces was taken by OM, SEM, EDS and micro-hardness tester. The results indicated that the grain size and strain energy are of great importance to improve the quality of interfacial bonding. Besides, the interfacial microstructure was found different from matrix and changed during the diffusion bonding process. Meanwhile, micro-hardness tests of the three kinds of joints showed that the micro-hardness in the interface was slightly higher than matrix in all the joints, resulted from the working hardening of the interface under the uniaxial pressure.