Microstructure evolution and strengthening mechanism of pulsed current diffusion bonding TiAl/Ti2AlNb joints with in-situ rapid hot deformation

Abstract

With the development of aero-engine toward high thrust-to-weight ratio, improving the strength of TiAl/Ti2AlNb joint has attracted considerable attention, as it is the key to manufacturing TiAl-Ti2AlNb composite turbine that combines high temperature resistance and weight reduction. However, the TiAl/Ti2AlNb diffusion bonded joint that is currently receiving the most attention is limited in strength by brittle interface structure and interfacial residual stresses, which cannot meet application requirements. In this study, a novel strategy of employing strong pulsed current to promote diffusion bonding of TiAl/Ti2AlNb joints and in-situ rapid hot deformation treatment was applied to improve this situation. This result shows that TiAl and Ti2AlNb alloys can be efficiently joined by pulsed current diffusion bonding (PCDB) with parameters of 950 ℃/10 min/10 MPa, the shear strength of the joint was 258.3 MPa. The subsequent in-situ rapid hot deformation treatment significantly strengthened the TiAl/Ti2AlNb joint, resulting in a shear strength of 443 MPa, which was 171.1 % of the pre-deformation strength. The formation of nanograined microstructure and precipitates acicular O phases after hot deformation-induced phase transformation of the diffusion bonding layers (DBLs) were the main strengthening mechanisms for the deformed joint. The large number of subgrain boundaries and the high dislocation density formed in the DBLs further increase the strength in this region. This study verified an effective of pulsed current diffusion bonding TiAl/Ti2AlNb joint with in-situ rapid hot deformation strengthening, providing a new strategy for obtaining high-strength dissimilar Ti-Al intermetallics joints.