Significant strength improvement in dissimilar TiAl/Ti2AlNb joints by pulsed-current diffusion welding with Ti-6Al-4V Interlayer: Multifaceted strengthening mechanisms and high-temperature performance

Abstract

The development of high-strength TiAl/Ti₂AlNb joints represents a pivotal and challenging research frontier in the fabrication of novel lightweight, high-temperature-resistant turbine components. In this study, we employed Ti-6Al-4V foils as an interlayer for the pulsed-current diffusion bonding (PCDB) of dissimilar TiAl/Ti₂AlNb joints, a strategy that yielded remarkable results. The tensile strengths of the newly-developed joints at both room temperature and elevated temperatures showed substantial improvements compared to previously reported TiAl/Ti₂AlNb joints. Specifically, the optimal PCDB joint exhibits a room-temperature strength of 607.8 MPa and a high-temperature strength of 527.9 MPa at 700 °C. The interfacial microstructure of this high-strength joint has unique structural features. The interlayer consists of an island-distributed α_p phase and a lamellar α+β structure, while the diffusion bonding layers (DBLs) on both sides are respectively composed of the bilayered α₂+α phases and the β phase strengthened by acicular α₂. The strengthening mechanisms of the joints are multifaceted. They encompass solid-solution strengthening and second-phase strengthening of the interfacial microstructure, optimization of the phase composition within the interface. The reduction of thermal stress caused by the addition of the interlayer is also considered a reason for the improvement of high-temperature strength. This research not only furnishes insights into the design and manufacturing of high-performance TiAl/Ti₂AlNb joints but also serves as a reference for their more extensive applications in cutting-edge aerospace and high-temperature engineering domains.