Coherent lattice matching in fusion-welded tantalum-titanium joints: Mechanisms of atomic diffusion and enhanced bonding strength

The integration of ultra-corrosion-resistant metal layers, particularly tantalum (Ta), with high-strength substrates presents significant opportunities for advanced engineering applications. However, fabricating Ta-based bimetallic structures with robust metallurgical bonds remains challenging. In this study, a novel fusion welding process was employed to join a 0.1 mm thick Ta foil to a 1.6 mm titanium (Ti) plate, enabling an in-depth exploration of the underlying bonding mechanisms. Comprehensive microstructural, compositional, and mechanical characterizations revealed that elevated welding temperatures induce notable grain coarsening in the Ti substrate, detrimentally affecting joint performance. Crucially, a ∼ 1 μm thick transition layer was identified at the TaTi interface, whose formation is governed primarily by the diffusion of Ta atoms into the Ti matrix. Advanced transmission electron microscopy (TEM) and selected area electron diffraction (SAED) analyses confirmed that this interfacial layer exhibits coherent lattice matching via a {01¯1}Ta // {11¯0}Ti crystallographic relationship, which underpins the exceptional bonding strength. Mechanical testing further showed that fracture occurs within the Ti base metal rather than the joint itself, attesting to the integrity of the metallurgical bond. These findings provide the first experimental evidence of coherent interfacial bonding in fusion-welded TaTi joints and advance the theoretical understanding by linking atomic diffusion kinetics and lattice-matching criteria to enhanced joint performance. This work offers valuable insights into the design and fabrication of high-performance TaTi bimetallic systems for future applications.