Microstructure and mechanical properties of Ti-6Al-4V cruciform structure fabricated by Coaxial Electron Beam Wire-feed Additive Manufacturing

Coaxial Electron Beam Wire-feed Additive Manufacturing (CAEBWAM), which is a novel additive manufacturing process, can produce fully dense alloy components with equiaxed β grains (EGβ) and isotropical mechanical properties and is considered as a potential manufacturing method for large-scale complex components. However, actual complex components inevitably include bonding regions, which are similar to welded joints, in the wire-feed deposition process, and limited knowledge is available on the microstructures and mechanical properties for this kind of regions. This work thoroughly studied the microstructures and mechanical properties of the Ti-6Al-4V alloy cruciform structure fabricated by CAEBWAM. It was found that the microstructure at the Bonding Zone (BZ) was composed of coarse columnar β grains (CGβ), continuous grain boundary α (α_GB) phase, and coarse α laths due to a higher temperature and poor heat dissipation condition. The average width of α lath in the BZ region was larger and the hardness was lower compared with those in the EGβ region. Tensile properties and fracture behaviours of the tensile samples extracted at cruciform structure were examined. The fracture tended to occur at the BZ region and exhibited a mixed fracture mode with trans- and inter-granular fractures. This work will improve the understanding of microstructures and mechanical properties for representative cruciform structure in wire-feed AMed components, which would be conducive to further progress of the actual complex components.