锻造-增材复合制造Ti-6Al-4V合金结合区显微组织及力学性能

The forging-additive hybrid manufacturing technology combines the advantages of traditional manufacturing in terms of efficiency and cost with the refined, flexible, and rapid prototyping characteristics of additive manufacturing. It provides an effective solution for efficient forming of large components. The bonding zone between the wrought-substrate and laser-deposition zones is the fundamental key in the properties of the entire component. In this study, laser solid forming (a powder-feeding laser additive manufacturing technology) was used to deposit bulk samples on a wrought Ti-6Al-4V substrate that contained a bi-modal microstructure. The microstructure in the bonding zone between the substrate and laser-deposition zones under different inputs of linear energy density were studied. The results show that the microstructure in the bonding zone varied from the bottom to the top due to the different influence extents of the heat source. Because of the lower peak temperature, the bi-modal microstructure at the bottom of the bonding zone still retained the initial morphology but contained a certain degree of coarsening. A mixed structure that contained equiaxed α, lamellar α, and a large number of secondary α in the middle of the bonding zone occurred with the increase in temperature and prolonging of the holding time. Meanwhile, the peak temperature of the upper part exceeded the β-phase transition temperature, which exhibited a Widmanstätten structure consisting of lamellar α and the so-called ghost area that was formed due to insufficient element diffusion. In the tensile tests, the fracture position of all bonding samples fabricated with various linear energy densities were very far from the bonding zone, indicating a better strength of the bonding zone than that of the wrought substrate and laser-deposition part. In addition, when the linear energy density was 100 J/mm, the yield and tensile strengths of the composite fabricated sample were larger than that with linear energy densities of 133 and 200 J/mm because the feature size of the α phase in the bonding and additive zones was smaller. Both the yield and tensile strengths of the hybrid fabricated specimen decreased with the increase in the linear energy density, whereas the elongation increased.