One major advantage of additive manufacturing is the high freedom of design, which supports the fabrication of complex structures. However, geometrical features such as combined massive volumes and cellular structures in such parts can lead to an uneven heat distribution during processing, resulting in different material properties throughout the part. In this study, we demonstrate these effects, using a complex structure consisting of three conic shapes with narrow cylinders in between hindering heat flux. We manufacture the parts via powder bed fusion of Ti6Al4V by applying a laser beam (PBF-LB/M) as well as an electron beam (PBF-EB). We investigate the impact of the different thermal regimes on the part density, microstructure and mechanical properties aided by finite element simulations as well as by thermography and X-ray computed tomography measurements. Both simulations and thermography show an increase in inter-layer temperature with increasing part radius, subsequently leading to heat accumulation along the build direction. While the geometry and thermal history have a minor influence on the relative density of the parts, the microstructure is greatly affected by the thermal history in PBF-LB/M. The acicular martensitic structure in the narrow parts is decomposed into a mix of tempered lath-like martensite and an ultrafine $\alpha$ + $\beta$ microstructure with increasing part radius. The EBM part exhibits a lamellar $\alpha$ + $\beta$ microstructure for both the cylindric and conic structures. The different microstructures directly influence the hardness of the parts. For the PBF-LB part, the hardness ranges between 400 HV${}_{0.5}$ in the narrow sections and a maximum hardness of 450 HV${}_{0.5}$ in the broader sections, while the PBF-EB part exhibits hardness values between 280 and 380 HV${}_{0.5}$.

Component porosity is a quality attribute in additive manufacturing (AM). One possibility for the non-destructive three-dimensional determination of porosity or pore shape is X-ray computed tomography (CT), which enables an investigation of the influence of AM process parameters on the appearance and characteristics of the pores. Since there is no porosity standard for CT, a traceable determination of the measurement uncertainty is not possible. Using a digital twin of the CT system, an estimation of the CT measurement uncertainty is in principle possible. In this contribution, experimental CT analyses of powder bed fusion samples made of Ti64 and PA12 are compared with CT simulations. The results show a size-dependent influence on the shape and detectability of the pores. Using the CT model, a simulated shape- and material-dependent probability of detection (POD) is calculated.

X-ray-computed tomography (CT) is today’s gold standard for the non-destructive evaluation of internal component defects such as cracks and porosity. Using automated standardized evaluation algorithms, an analysis can be performed without knowledge of the shape, location, or size of the defects. Both the measurement and the evaluation are based on the fact that the component has no internal structures or cavities. However, additive manufacturing (AM) and hybrid subtractive procedures offer the possibility of integrating internal structures directly during the building process. The examination of powder bed fusion (PBF) samples made of Ti64 and PA12 showed that the standardized evaluation methods were not able to identify internal structures correctly. Different evaluation methods for the CT-measured values were analyzed and recommendations on a procedure for measuring internal structures are given.

The component porosity is a quality attribute in additive manufacturing (AM). One way for a non-destructive three-dimensional determination of the porosity or the shape of pores is X-ray computed tomography (CT), which enables to investigate the influence of AM process parameters on the appearance and characteristics of pores. Due to the lack of a porosity standard for CT, a traceable measurement uncertainty determination is not possible. To investigate the capability of CT for porosity analysis, measurements of an optically measurable glass specimen that contains highly spherical pores are used to validate results from a digital twin of the CT system. The influence of a fixed gray value threshold for the porosity analysis algorithm and the deviation of the surface determination are investigated.