## 4 Results  
A binarized image of the sample array is shown in Figure 3a along with the parameters chosen for each sample. Figure 3b shows the average porosity for each sample. Porosities between 0.37% and 1.58% have been achieved. The highest porosity yields from the coldest processing conditions are given by the highest scan speed (1400 mm/s) and lowest laser power (285 W). Decreasing the scan speed from the highest porosity decreases porosity to a value of 0.37% at a scan speed of 950 mm/s. However, other combinations, such as (1250 mm/s, 330 W), may lead to a slightly increased porosity of 0.43%.  
The mechanical properties of a component are weakened by defects. In addition to a low porosity, a small pore size is also to be targeted. Characteristic for the pore size distribution is the area median diameter d\({}_{50,2}\) (Figure 4a) as well as the span value (Figure 4b), which indicates the width of the distribution. For the previously discussed conditions that yielded 0.37% and 0.43% porosity, we obtained a \(d_{50,2}\) of 92 and 78 um with a span of 1.18 and 1.27, respectively. The smaller median pore size diameter was related to a wider size distribution in this case. On the other hand, the largest median diameter of 248 um yielded in the narrowest span value of 0.83, while the largest span value of 1.83 related to a small median diameter of 87 um.  
Figure 3: (a) Binarized image of sample array, (b) relative porosity of samples.  
A large pore diameter with a small span value means that the porosity is governed by large pores, which is very critical regarding material properties. In this case, there are many large pores which can act as an initiator for a crack. On the other hand, smaller diameters with a large span value result in a wide distribtion with few large pores.  
It is well known from high cycle fatigue studies that the largest defect in a part will usually initiate its failure. Not only the size, but also the shape of the defect plays a major role. For example, an existing crack will propagate more easily than a new crack will develop from a spherical pore. As a result, cracks should be avoided. Figure 5a shows the maximum pore size for each sample. For the larger pore sizes with low span values, the maximum pore diameter is slightly higher than the median value. The highest scan speed of 1400 mm/s with a maximum laser power of 315 W yields in the lowest maximum pore sizes of 116 \(\upmu\)m.  
The porosity fraction of each defect is shown in Figure 5b. Lack of fusion defects and unmelted particles are the dominant defect types. There is no significant contribution of gas pores for this material and process conditions and cracks make a minor contribution to  
Figure 4: (**a**) Area median diameter pore-size distribution, (**b**) span \(\sigma=(d_{90}-d_{10})/d_{50}\) of distribution.  
Figure 5: (**a**) Maximum pore size, (**b**) porosity fraction of each defect type and absolute porosity caused by cracks (left number) and gas pores (right number) in ppm.  
porosity. While many cracks were found at the condition (1400 mm/s, 285 W) with an area fraction of 415 ppm, their appearance was a magnitude less frequent in all other conditions.  
Finally, we evaluate the shape accuracy of the samples from the ratio sample perimeter from image analysis and the theoretical sample perimeter (Figure 6). Since a larger value represents a higher deviation from the targeted shape due to surface roughness or surface defects, small values are to be aimed at. Cold conditions such as (1400 mm/s, 285 W) lead to a high value of 3.37 due to incomplete melting and powder bonding at the surface, hotter conditions such as (950 mm/s, 330 W) yield in the lowest value 2.34. In this study, we have not used specific contour parameters, so that the shape accuracy will be a result of porosity optimization.