Effects of Pore Geometry on the Fatigue Properties of Electron Beam Melted Titanium-6Al-4V

Abstract

Current percent-porosity based quantification of pores in additively manufactured parts does not provide information about the size, shape, and distribution of pores throughout a build. Such information is necessary to understand the conditions under which the part was printed as well as its mechanical reliability. This research, through a combination of fatigue testing and microstructural characterization demonstrates a method by which the internal porosity can be characterized and using the knowledge of the pores differing formation mechanisms to inform future design and build strategies. Though the test bars were printed under nominally identical conditions, ignoring lack-of-fusion, batch 1 had 34 pct fewer lenticular pores and 147 pct more spherical pores than batch 2 which shows that the actual print conditions of these parts varied substantially as would their as-printed mechanical reliability. To quantify this difference extensive optical, SEM, and EBSD metallographic studies were conducted on several samples from these bars as well as the fracture surfaces to gain an understanding of the porosity’s shape, size, and location. The comparison of these datasets along with knowledge of the pore’s evolution allows for the optimization of future build strategies and the more accurate prediction of the resulting as-built mechanical properties.