Abstract: The tissue evolution of the heat-affected zone of Ti-6Al-4V (TC4) titanium alloy composite fabricated by laser-directed energy deposition + forging technology is studied, and the tissue characteristics and mechanical properties of the three post:composite fabricated TC4 titanium alloys after heat treatment are analyzed and compared. The results show that the composite fabricated specimens can be divided into three regions with different microstructures in the forging zone, heat-affected zone and additive zone. The microstructure morphology of the heat-affected zone has the dual characteristics of bimorphic and mesh basket organization. The isometric α-phase in the heat-affected zone on the forging side grows under the influence of heat input and the content increases significantly, while a large number of fine lamellar α-phase is formed in the heat-affected zone on the additive zone side. The width of α slats in the heat-affected zone of the specimens after annealing at 600℃ and 800℃ are similar, but some equiaxed α phases existed in the heat-affected zone of the specimens annealed at 800℃, and the double annealing process at 975℃ caused significant coarsening of the grains in the heat-affected zone. Under the same heat treatment process, the mechanical strength properties of the composite fabricated TC4 titanium alloy specimens are higher than those of the standard TC4 forgings and TC4 specimens fabricated with the same process parameters, but the post-fracture elongation is about 31% lower than that of the fabricated specimens. In the heat treatment process, the best mechanical strength properties are obtained for the 600℃ annealed specimens, and the yield strength is increased 41 MPa compared with the 975℃ double annealed specimens, and the differences in post-extension and face shrinkage between the three heat treatment specimens are small.

Key words: TC4 titanium alloy, laser-directed energy deposition, hybrid manufacturing, heat treatment, microstructure, mechanical properties