Effect of support structures on Ti-6A1-4V overhang parts fabricated by powder bed fusion electron beam additive manufacturing

The effects of the two support structures, thin-wall tooth contact (TC) and solid-gap (SG), on the Ti-6A1-4V parts fabricated by powder bed fusion electron beam additive manufacturing were investigated. In the Y-plane of the overhang, equiaxed beta ' microstructure formed initially and gradually grew into a wider columnar structure with its width about 3 times of that iRn the solid section. Fine alpha/alpha' and beta phases were identified within the 13' grains, in which the content of alpha ' increases from the bottom to the top of the part and alpha/beta ' phase presents strong textures of (0001) and (1120) parallel to the build-direction. In addition, more defects were observed in the overhang than the solid, especially at the interface between the solid and the overhang sections which also induced the stress concentration. Compressive residual stresses were revealed in the parts with some points showing minor tensile residual stresses. Compared to the SG part, the TC part had a lower Vickers hardness. The solid part under the SG part acted as a heat sink and enhanced heat dissipation during the manufacturing process, which affected the thermal gradient and improved the microstructures and mechanical properties in the overhang. The teeth in the TC part did limit the occurrence of the wrapping phenomenon. Taking advantages of the two designs, a new support design, SG support with teeth at the tip-end of overhang, is recommended.