In-situ investigation on the anisotropic behavior of the additively manufactured dual-phase Ti-6Al-4V alloy

In this work, in-situ SEM tensile investigations were performed to study the fracture mechanism, anisotropic behavior, and the defect effects of selective laser melted (SLM) and then heat-treated Ti6Al4V with a dual-phase alpha + beta lamellar structure in three loading directions (90 degrees /45 degrees /0 degrees to the substrate). The results showed that the surface steps formed due to the deformation mismatch during the plastic stage. The initiation of microcracks was mainly due to the separation between the adjacent lamellae or the lamellae fracture. Near-surface defects could induce the strain concentration and then premature failure, whereas the defects deep inside the specimens presented little effect on ductility deterioration. Based on the grain orientation data, the calculation of most likely active slip systems illustrated the significant difference in the slip traces between the two adjacent alpha laths accounted for the deformation mismatch and the arising of surface steps. The difference in the overall Schmid Factors revealed the inhomogeneous deformation between the adjacent columnar prior beta grains. Finally, the theoretical analysis was conducted and well verified by the experimental results helping a further understanding of the deformation mechanism.