Relationship between microstructure and mechanical properties of TiAl/Ti 2 AlNb joint brazed using Ti-27Co eutectic filler metal

Partially substituting TiAl alloys for Ti2AlNb alloys has been identified as an effective approach to realize the weight reduction of aircraft engines. Therefore, joining of TiAl alloy to Ti2AlNb alloy is important and meaningful. In this study, TiAl alloy and Ti2AlNb alloy were successfully brazed at 1080–1140 °C for 10 min using Ti-27Co (wt%) eutectic filler metal. Scanning electron microscope (SEM), energy dispersive spectrometer (EDS) and transmission electron microscope (TEM) were employed to characterize the interfacial microstructure of the joints. The results showed that α2-Ti3Al, β-Ti, TiCo, Ti2Co and B2 phases were formed in the brazing seam of the joints. As the brazing temperature increased, the thickness of diffusion layer in the TiAl side became thicker correspondingly. Higher brazing temperature accelerated the diffusion of Co element into the substrates, resulting in the disappearance of band-like Ti2Co phase and the growth of acicular Ti3Al phase. The highest shear strength of the joints was 223 MPa when brazed at 1100 °C for 10 min. The hardness and elastic modulus of the phases in the joint were measured by nano-indentation to show the plastic deformation capacity. In addition, the microstructure evolution mechanism of the joints was put forward based on the experimental analysis.