## 2 Materials and Methods
### Industrial Computer Tomography  
Industrial \(\upmu\)-CT is a non-destructive investigation method where parts are scanned with X-rays. During the CT process, high-energy X-ray radiation was emitted and directed onto the testing part. The part was mounted on a rotating manipulator. During the interaction between the X-rays and scanned part, a quantity of the radiation gets absorbed, and the radiation traversing the test part is collected by a detector, usually a CCD camera [38]. If defects and/or inhomogeneities are located inside the investigated part, the absorption at these locations is less comparable to the fully dense material. Hence, more radiation is detected and defects can be located via analysis software. For the presented research a voltage of 110 kV and a current of 100 \(\upmu\)A were used, resulting in a voxel size of 9.27 \(\upmu\)m. In order to scan 3D volumes a series of 2D images from different angels were made and afterwards reconstructed by the software YXLON Reconspooler Workspace 1.4.4.0. The reconstructed volume was transferred to the VG Studio MAX 3.3.4 software. In order to analyse the volume correctly, an optimisation must be performed before further investigation. In Figure 2a a reconstructed volume and in Figure 2b its respective grayscale histogram are presented. If the threshold and/or the brightness is not optimised, a falsification of the analysis is most likely possible, due to poor contrast between material and defects. By changing the light-blue line in the histogram (see Figure 2b,d), the contrast between defects (or background) and the specimen can be influenced. In addition, the brightness of the specimens can be differed in an attempted to increase the contrast between defects and specimen. In Figure 2b, the greyscale histogram of the scanned specimen as scanned is shown. Compared to that, in Figure 2d an adjustment of the light-blue line was applied, and therefore the contrast and brightness settings are changed. The impact of these changes can be compared in Figure 2a,c. Furthermore, if the background colour is changed to the colour black the contrast is increased. From the results, it is clear that the contrast and brightness must be optimised to increase the detectability of internal defects. Figure 2: Different greyscale histograms and their respective influence on the scanned part: (**a**) reconstructed volume, as scanned, without any optimisation of brightness and contrast; (**b**) greyscale histogram for (**a**); (**c**) reconstructed volume with optimisation of brightness and contrast; and (**d**) greyscale histogram for (**c**). The histograms in (**b**,**d**) have the grayscale from 0-32000 (16-bit grayscale figure) as the x-axis, and the logarithmic intensity is given as the y-axis. Defects affect the mechanical behaviour of load-bearing parts either due to notch effects, crack nucleation sights or, in extreme cases, load-bearing cross-section reduction [23]. In order to investigate the influence of defects a Deben CT5000 tensile test stage was used. The stage, see Figure 3, can operate in a tensile or pressure mode with a force of up to 5000 N. For these measurements the sample geometry had to be designed in such a way that the maximum force of the tensile tests did not exceed 5 kN. Consequently, a small test cross-section and thin sample material must be used, see Figure 4. In order to manufacture these tensile test specimens, three blocks with the dimensions of 40 \(\times\) 20 \(\times\) 120 mm were first EB-PBF-manufactured. Subsequently, the heat treatments (STA and BASCA) were performed on individual blocks; afterwards, the tensile test specimens, according to Figure 4, were shaped out of these blocks using an electro-erosive process as well as a laser cutter. Due to the extra energy transported into the specimens during the laser cutting an oxygen analysis using Elementar's inductar EL cube was conducted. It showed an insignificant oxygen pickup. In Figure 5 the microstructure of an in situ specimen after a laser cut can be seen.