Diffusion Bonding Between TiAl And Ti Alloys And The Mechanical Properties Of The Joints At Elevated Temperatures

γ-TiAl alloys exhibit low density, excellent properties at high temperatures, which are one of the most promising materials for high temperature application. Understanding the bonding behaviors of the alloys with themselves and with other alloys is helpful to their applications. In this thesis, a new diffusion bonding approach (named LMS) was introduced to the bond between TiAl and Ti6Al4V. In this approach, laser rapid solidification surface modification was first conducted on the pre-bonding surfaces ofγ-TiAl and Ti alloys. With this method, a sound bond was achieved at the diffusion conditions of 900℃/80MPa/2h. The bend strength of the joint achieves 92.9% of the strength of TiAl matrix. On the basis of understanding of the microstructure of bond interface and bonding mechanisms, the mechanical properties at high temperatures, especially creep behavior, of the joint obtained by LMS was investigated, comparing with that of the joints obtained at same diffusion bondingcondtions by the normal diffusion method without laser surface modification( named NLMS), and the effects of the mircrostructures on the high temperature properties and fracture mechanism were discussed. The results indicated that the tensile fracture strengthes at 400-600℃are lower than that of the TiAl matrix. The strength of the LMS joint at 400℃is higher than that of the NLMS joint, but they are almost identical at 600℃. The fracture of both joints occurred in the bond at 400-600℃, and the fracture modes were strongly dependent on the temperature. The higher strength of the LMS joint is due to its perfect metallurgical bonding. At the temperature range of 400-600℃, the creep deformation concentrated in the Ti matrix in both joints, which was controlled by dislocation climb. The creep resistance of the LMS is much higher than that that of NLMS joint, but slightly lower than that of Ti matrix. The creep fracture of both joints occurred at the bonding interface or near the interface. The bonding interface is weak during creep, and the interface strength and fracture mechanism decided the life time of creep of the joints. As a result, the new diffusion method used in the present study is a promising solid bonding method for bonding between TiAl with other alloys.