Interfacial reaction between Ti-Al binary alloys and high carbon steel

Diffusion bonding of Ti-Al binary alloys (Ti-10 to 40 mol% Al) to high carbon steel was carried out between 1073 and 1273 K for 0.9 to 8.1 ks in a vacuum, and the effect of the alloy composition on the interfacial microstructures and the bonding strength was investigated. Three regions, which were composed of reaction products with Ti, Al and Fe, a TiC layer, and ferrite, were formed around the interface, regardless of the alloy composition. The thickness of each region changed with an increase in the Al content in the Ti-Al alloy. In general, the TiC layer formed in Ti/steel joints is known to act as a barrier for diffusion of constituent elements across the interface and to inhibit the formation of other reaction products. In this study, the barrier effect of the TiC layer was overcome by the existence of Al. Although the Ti-Al/steel joints showed a relatively high bonding strength of more than 150MPa in many cases, the joint with Ti-20mol% Al alloy separated near the interface promptly after bonding treatment at 1273 K for 3.6 and 8.1 ks. The details and the application of the separation phenomenon are discussed.