Unveiling microstructural heterogeneity and strain redistribution mechanisms in hybrid-manufactured Ti6Al4V

Abstract

Hybrid-manufactured titanium (Ti) alloys exhibit significant challenges in achieving uniform mechanical properties due to the heterostructured interfaces. In this study, we systematically investigated the microstructural evolution, crystal orientation, and tensile strain distribution in hybrid-manufactured Ti6Al4V, focusing on flow stress, strain partitioning, and dislocation mobility at various interface conditions. Due to the incomplete phase transformation, a unique ghost structure forms in the heat-affected zone (HAZ) between the deposition zone and substrate. This structure, influenced by the residual α, exhibits significant variant selection. The unique needle-like α and α blocks inside the ghost structure effectively reduce the local internal strain. Numerous mixed dislocations in the rim of the ghost structure improve the strain hardening. The gradient microstructure in HAZ plays a pivotal role in strain redistribution, enabling the hybrid-manufactured Ti6Al4V to outperform traditional forged production in tensile properties. The hybrid-manufactured Ti6Al4V achieves an ultimate tensile strength of 1018 MPa and an elongation of 10.5 %. This work provides critical insights into the mechanisms underlying heterogeneous deformation in hybrid-manufactured Ti alloys and offers practical guidance for manufacturing complex and high-performance load-bearing components.