Study of keyhole-porosities in selective laser melting using X-ray computed tomography

The occurrence of keyhole porosity in selective laser melting (SLM) has so far not been quantified systematically using X-ray computed tomography (X-CT). In this study, keyhole porosity in selective laser molten Ti-6Al-4V grade 23 parts was analyzed using post-process characterizations. Single tracks were produced with optimum, high volumetric energy density and low volumetric energy density parameters on the top of SLM substrate. High volumetric energy density was achieved by either (i) high laser power and optimum scan speed to study the effect of laser power or (ii) optimum laser power and low scan speed to study the effect of scan speed. Keyhole porosity is sensitive to the SLM process parameters. It was observed by using X-CT that a high amount of keyhole porosity was formed below the line scan produced with a high volumetric energy density achieved by optimum laser power and low scan speed; however, a line scan produced with same volumetric energy density but achieved by high laser power and optimum scan speed resulted in less or no voids. The X-CT porosity analysis helped to understand the size, shape, location, and number of keyhole pores that were formed.