Diffusion Bonding of TiAl Alloy to Eutectoid Steel and its Interfacial Self-destruction Behavior

Interfacial microstructures and bonding strength of TiAl alloy/eutectoid steel joints have been investigated from the viewpoint of diffusion barrier effect of carbide layer formed at the interface. Diffusion bonding was performed at 1073 to 1273 K for 3.6 ks in a vacuum, and then several specimens were heated at 1073 to 1273 K for 10.8 to 86.4 ks in evacuated quartz tube to examine the growth behavior of reaction layer. The joint has essentially four kinds of the reaction layers. They are composed of two layers with Ti, Al and Fe elements, TiC layer containing Fe-Al compounds and ferrite layer. This indicates that the joint is difficult to have stable diffusion barrier layer consisting only of the TiC due to contribution of Al element to the interfacial reaction. Although the joint bonded at 1073 K shows high bonding strength of 160 MPa, the strength dramatically decreases with increasing bonding temperature. In addition, self-destruction phenomenon is recognized at the interface in the joints heat-treated at 1173 and 1273 K, and the origin is also discussed.