Experimental investigation on the accuracy of surface topography measurements of additively manufactured metal parts scanned by X-ray micro computed tomography

Additive manufacturing of metals is increasingly used for producing highly customizable parts, including complex and internal geometries. However, such parts are characterized by surface topographies that are difficult to be measured with contact or optical techniques, due to several complexities, including: presence of undercuts, non-totally melted powder particles and overhangs. Micro X-ray computed tomography has recently started to be considered as an alternative technique for topographical measurements of additive manufacturing surfaces, as it is capable of measuring also non-accessible surfaces and micro-scale surface features including undercuts. This work proposes a new method to determine the accuracy of surface topography measurements obtained by computed tomography as well as by optical areal measuring techniques. Ti6Al4V specimens were produced by selective laser melting. Specifically designed markers were then micro-milled on the surfaces of interest, to allow for accurate alignment and comparison of different areal topography measurements. Reference 2D roughness profiles were obtained after cutting and polishing the specimens at specific locations, by measuring the resulting cut-sections using an imaging probing system.