Introduction The properties of hybrid - manufactured Ti6Al4V show significant cross - regional heterogeneity due to the differences in the processing conditions of the forged substrate and the DED part. The forged matrix produces fine equiaxed β grains and equiaxed / bimodal α phases, with good strength, ductility and mechanical isotropy; the DED part forms coarse columnar β grains and basket - weave or Widmanstätten structures due to rapid melting and solidification, with high strength but low ductility and obvious mechanical anisotropy. The microstructure and properties in the bonding region between the two change in a gradient, which improves the interface bonding strength but introduces complex mechanical response behaviors and affects the overall performance of the hybrid - manufactured part. The purpose of this study is to construct a load - bearing model including regional anisotropy and interface characteristics, focusing on the influence of plane and curved interface geometries on tensile response behaviors.
Materials and Methods Commercial spherical Ti6Al4V powder and forgings were used. After the powder was vacuum - dried, the substrate was processed into flat and curved interfaces. Through microstructure observation, the interface width in the finite - element model was determined to be 2 mm, and the mechanical properties of the DED part, heat - affected zone (HAZ) and forged substrate were accurately characterized. Finite - element models of tensile specimens with plane and curved interfaces were constructed to analyze the stress - strain fields changing with time during the tensile process.
Results and Discussion The microstructure observation results show that under both plane and curved interface conditions, the grain structures are basically the same, and the interface morphology has little influence on the microstructure. The grain structure of the DED part is mainly β - columnar grains, and the thickness of the heat - affected zone (HAZ) is similar. The DED part has obvious mechanical anisotropy, with large differences in properties along the deposition direction and the perpendicular direction, and its strength is higher than that of the forged substrate.
The finite - element model analysis shows that during the tensile process, the stress distribution of specimens with different interfaces is uneven. When the total strain reaches 1.57%, all regions of the hybrid - manufactured specimen are in the plastic deformation stage. The stress of the forged substrate is higher than that of the DED part and is accompanied by stress concentration, and the stress is concentrated near the interface. When the total strain increases to 4.16%, the uneven stress distribution is more obvious, and a larger stress - concentration area is formed in the softer forged substrate, which coincides with the final fracture location. The stress in the heat - affected zone of the plane interface shows a gradient distribution with high values on both sides and a low value in the middle, and the stress in the heat - affected zone of the curved interface shows a gradient distribution with a high value in the middle and low values on both sides.
Conclusions This study systematically explored the influence of interface morphology on the tensile properties of Ti6Al4V alloy by laser hybrid additive manufacturing. The importance of the interface width to the model was clarified, the mechanical properties of each part were accurately characterized, and the changes in the stress - strain fields of different interface morphologies during the tensile process were revealed through finite - element model analysis. These findings provide a theoretical basis for optimizing the interface design to improve mechanical properties, have important guiding significance for additive manufacturing, and are helpful for promoting the future development of additive manufacturing of components with inhomogeneous microstructures.