Discovering the role of the defect morphology and microstructure on the deformation behavior of additive manufactured Ti-6Al-4V

The defects remain a significant issue for additive manufactured titanium alloys, which hinders their further market penetration. In this work, we proposed a new understanding of the inhomogeneous microstructure for-mation affected by defects with detailed EBSD characterization, and how the defects and inhomogeneous mi-crostructures determined the strain accumulation behavior by in-situ SEM tensile testing. Smaller prior beta grains and coarser alpha laths were identified around the defects. In-situ tensile behavior investigations revealed that irregularly-shaped and elongated defects with high stress intensity factor (Delta KI) could induce severe strain accumulation, showing that the defect morphology was the primary factor that could determine the strain accumulation behavior. In the meantime, the inhomogeneous microstructures around the defects could further contribute to the strain accumulation, with the coarser alpha laths more favorable for deformation and stronger microtexture for easier slip transmission. In addition, microcracks were found initiated from a spherical pore with small loading, and arrested due to the negligible strain accumulation. Further characterization showed that oxidation, which was found more probable in spherical pores, was the cause of this microcrack initiation.