Ti-Sn binary alloys (Ti-5 to 20 mol% Sn) were diffusion-bonded to high carbon steel between 1073 and 1273 K for 3.6 ks in a vacuum to investigate the influence of the alloy composition on the interfacial microstructures. Ti-5 and 10 mol% Sn alloys were attached firmly to the steel at a bonding temperature of 1273 K. A continuous TiC layer was formed along the interface, while voids were observed between the TiC layer and the steel. Although the joints with Ti-15 and 20 mol% Sn alloys were also prepared at 1273 K, these joints separated near the interface after the bonding treatment. The TiC layer was formed in the separated surface of Ti-Sn alloy, and Fe in the steel diffused into the Ti-Sn alloy. This indicates that the Ti-15 and 20 mol% Sn alloys established contact with the steel at elevated temperatures until just before the separation. The specimens bonded at 1173 K also denoted the same tendency. However, the Ti-15 mol% Sn/steel joint bonded at 1073 K showed a shear strength of more than 50 MPa. The mechanism and the application of the interface separation are discussed on the basis of the microstructural observations.

Diffusion bonding of Ti-15 mol% Sn alloy to various iron materials was carried out in the temperature range of 1 073-1 273 K for 0.9-14.4 ks in a vacuum to verify interface separation, a phenomenon that has been observed between Ti-20 mol% Al alloy and high-carbon steel after bonding treatment at 1 273 K for 3.6 ks. Four types of carbon steel and one type of cast iron were used as an opposite material for the Ti-15 mol% Sn alloy. In the case of steel having a relatively low carbon content, a sound joint without defects like a gap at the interface was obtained through bonding treatment at 1 273 K for 3.6 ks. However, the joints with high-carbon steel and cast iron, which were fabricated at 1 273 K for 3.6 ks, had gaps at the interfaces, and several specimens separated near the interface promptly after bonding treatment. The separated surfaces of the high-carbon steel and cast iron were relatively smooth. A microstructure corresponding to the grain boundary and pearlite was observed in the surfaces. It was found that this phenomenon depended on the heating temperature and the holding time. These features were consistent with those of interface separation previously reported in the case of Ti-20 mol% Al alloy. Therefore, it is concluded that the separation phenomenon was caused by interdiffusion across the interface between the titanium alloy and the iron material.