Uncovering the different roles of lack-of-fusion and keyhole defects on the tensile behavior of additively manufactured Ti-6Al-4V alloy

As two common defects, both lack-of-fusion (LOF) and keyhole can degrade the mechanical property of additively manufactured metals, but the underlying mechanism has never been clarified thoroughly. Herein, by varying the scanning parameters, we introduced LOF and keyhole defects into different Ti-6Al-4V specimens and analyzed their mechanical responses via in situ tensile tests under X-ray computed tomography (XCT). It was found that the different defects have extremely different effects on the tensile properties. As for the samples with intentionally introduced LOF defects, the defects propagate rapidly along the loading direction and coalesce into larger defects transversely, which results in severe strain localization and premature failure. In contrast, the samples with intentionally introduced keyhole defects show much slower defects coalescence with much lighter strain localization during tensile deformation. Consequently, the intentionally introduced keyhole defects have negligible effect on the tensile properties, while the intentionally introduced LOF defects degrade the yield strength and elongation by 17 % and 64 %, respectively. Our findings may provide guidance for the development of high-performance metallic components via additive manufacturing.