Fabricating carbon steel/Ti composites through forge-welding via in-situ interfacial reaction of Ni coating

Solid-state bonding is paramount in joining dissimilar materials, often combined with metal forming, such as forging, rolling and extrusion, to fabricate composites with a designed structure. Owing to its superior mechanical properties and low density, the carbon steel/Ti composite structure is attractive in automotive and aerospace industries but is difficult to fabricate due to the decarburization of carbon steel's faying surface. In this work, a carbon steel/Ti6Al4V composite structure was first fabricated via a forge-bonding method with the assistance of a Ni coating layer. Results show that the Ni layer on the faying surfaces precludes the decarburization of the steel and the growth of the TiC phase so as to improve the bonding quality. Meanwhile, the in-situ eutectic reaction between the Ni layer and β-Ti was observed. As a result, a seamless bonded interface with the total elimination of the Ni layer can be obtained. The bonding strength was examined to establish the relationship between bonding windows, microstructure and the resulting mechanical properties. An experimentally validated thermal-mechanical finite element model was also developed to understand the process-dependent interface evolution. This work opens a new avenue for fabricating carbon steel/Ti6Al4V composite, extending the flexibility of achieving complex structures by combining solid-state bonding with other metal-forming technologies.