Regulating the interfacial microstructure in TiAl/Ti2AlNb vacuum diffusion bonded joints for superior mechanical performance

Dissimilar material joining between TiAl and Ti2AlNb intermetallic alloys is the key to integrating the attractive properties of these lightweight structural materials in one hybrid component. However, some intractable problems, such as brittle reaction layers, residual thermal stress at the interface, and poor plasticity at ambient temperature, hamper its application. To overcome these deficiencies, diffusion bonding of intermetallic TiAl alloy to Ti2AlNb alloy using a series of newly designed Ti100-xMox (x = 2.56 ∼ 14.26 at. %) interlayers was investigated. By regulating the Mo content in the interlayer, a fine α-Ti layer and a gradient α-Ti + β-Ti composite layer were regulated in the reaction zone when the Mo content was 8.09 at. %. Such elaborately tailored interfacial microstructure led to superior mechanical performance for which the plasticity markedly exceeded the TiAl substrate while maintaining a considerable tensile strength (402 MPa). The improvement of mechanical performance of bonded joints could be attributed to the competition and collaboration between initiation of cracking in the TiAl/Ti91.91Mo8.09 interface and stress-induced martensitic transformation in the interlayer. Tensile testing showed that the bonded joints finally ruptured at the brittle α2 reaction layer. The results in this paper provide important insights into fabricating high-quality TiAl-based hybrid joints by diffusion bonding.