Superior strength-ductility synergy in micro-deformation diffusion bonded Ti-6Al-4V achieved by gradient nanostructured surfaces

Micro-deformation diffusion bonding of Ti-6Al-4V alloy is a key solid‑state joining process for manufacturing components with intricate internal channels, as required in diffusion bonding additive manufacturing (DBAM). A critical challenge lies in achieving sound joint performance while limiting uniaxial deformation to below 1% to preserve geometric accuracy. Here, gradient nanostructured surface layers about 25 μm thick were fabricated on Ti‑6Al‑4 V via high‑pressure waterjet peening. The nanostructured surface, with an average grain size of 80 nm at the outermost region (statistically measured over a 2.25 μm × 2.25 μm area immediately beneath activated surface), greatly enhanced interfacial diffusion and void closure during bonding at a uniaxial deformation of approximately 0.8%. The bonding ratio rose from 83.2% for non‑activated joints to 99.1% and 100% for unilaterally and bilaterally activated joints, respectively. Complete interfacial recrystallization and full interface migration were achieved, forming a fine‑grained equiaxed α phase band. Compared with non‑activated joints, the activated joints showed a 6% increase in ultimate tensile strength (975 MPa) and a 646% rise in fracture elongation (19.4%), outperforming even the base metal. This synergy stems from void elimination, which suppressed premature cracking, and a recrystallized interfacial microstructure that provided a remarkably high and sustained work-hardening rate (maintained above 1100 MPa up to a true strain of 0.117), demonstrating the joint's enhanced capabilities for dislocation accommodation. The approach successfully decouples the traditional trade‑off between precision and performance, offering a viable route to high‑integrity DBAM components with complex internal features.