Enhanced strength-ductility synergy in hybrid additive manufactured Ti–6Al–4V via interlayer friction stir processing assisted laser-directed energy deposition

Abstract

The strengthening and toughening of AM-ed Ti–6Al–4V alloy remain persistent challenges in engineering applications. This study proposes a hybrid additive manufacturing (HAM) strategy integrating low-energy density laser-directed energy deposition (L-DED) with a reduced molten pool diameter (∼φ1.5 mm) and friction stir processing (FSP). The microstructure evolution during hybrid additive manufacturing was investigated through multiscale characterisation and thermal field simulation. The results show that the L-DED-produced sample exhibits near-equiaxed grains (average width: ∼333 μm) comprising refined acicular α and martensitic α′ phases. In contrast, the HAM-processed hybrid zone demonstrates exceptional thermal stability during subsequent thermal cycling, maintaining an ultrafine-grained structure (average size: 5.04 μm) dominated by α + β lamellar structure and globular α phases. The HAM samples achieve a strength-ductility synergy with an ultimate tensile strength of ∼974.8 MPa and elongation of ∼20.4%, demonstrating the efficacy of this hybrid approach. This work establishes a viable pathway for fabricating high-performance titanium alloy components via hybrid-optimised additive manufacturing.

Keywords

• Laser-direction energy deposition
• friction stir processing
• Ti–6Al–4V alloy
• mechanical property
• microstructure evolution