document: MicroCT has been applied to AM parts in various forms. Some preliminary results demonstrating the visualization of defects including porosity in AM components were reported in [6]. In another study, the porosity structures in parts built with improper settings were investigated [7]. In this work, the average porosity ranged from 0.1–0.5%, and large pores were observed which followed the build direction and may be attributed to the electron beam raster and overlap pattern. This was followed by more recent reports of the porosity distribution as a function of build strategy for electron beam melted samples with average porosity < 0.2% [8]. In another study, similar porosity images from microCT were reported at levels above 0.2% average porosity [9,10]. Very recent work reports similar images and may indicate that the porosity structure depends on the build direction [11]. Other applications of the use of microCT to characterize AM parts include the comparison of the part to its design model [12] and the characterization of surface roughness of such parts [13]. In the present work, the aim is to demonstrate a specific type of defect present at very low average porosity levels below 0.01%, and which does not follow the build direction as in some other reported examples. We also demonstrate how this porosity structure changes after Hot Isostatic Pressing (HIP) treatment of the same sample.
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