# Developing Tungsten-Filled Metal Matrix Composite Materials Using Laser Powder Bed Fusion
## 3 Results  
### Process Parameter Development  
For the processing of MMC materials, suitable process parameters need to be developed. In order to investigate the impact of different process parameters, a randomized full factorial DoE (Design of Experiment) experimental plan was created based on the starting parameters. The main factors--laser power and exposure speed--were varied on two levels by ca. \(\pm\) 10% relative to the central point of the experimental plan. The hatching distance as the third common main factor was not adapted [11]. Tungsten content started at 40 vol%. This value is found to be one of the highest particle volume contents investigated in L-PBF studies regarding steel-based MMCs [7]. The central point of the 40 vol% experimental plan presents the starting parameters developed for MS1 by the methodology of [PERSON] et al. [11]. In each experimental plan, three control points were used for the center. Each sample was measured three times by the Archimedean principle. Each plan was executed once. All experimental plans are listed in Table 1. The hatch distance was set as 0.09 mm. However, the final experimental plan (W, 60 vol% 2 nd adaption) was repeated with different hatch distances of 0.07 mm and 0.05 mm to check its influence. As the overall picture regarding density does not change, only the measurements for 0.07 mm are depicted in Figure 1. Slim experimental plans were chosen in order to keep the number of samples within one build cycle low. This can prevent cross-contaminations by side products, faulty recoating or unsuitable positioning in the building volume (e.g., side positions). The theoretical density (\(\rho_{\text{theo}}\)) that can be expected from the corresponding tungsten content (V\({}_{\text{Tungsten}}\)) is calculated by the ideal linear rule of mixtures  
\[\rho_{\text{theo}}=\rho_{\text{Tungsten}}\cdot\text{V}_{\text{Tungsten}}+ \rho_{\text{MS1}}\cdot(1-\text{V}_{\text{Tungsten}}), \tag{2}\]  
with \(\rho_{\text{Tungsten}}=19.25\) g/cm\({}^{3}\) and \(\rho_{\text{MS1}}=8.1\) g/cm\({}^{3}\). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multicolumn{2}{c}{**W, 40 vol\%**} & \multicolumn{2}{c}{**W, 50 vol\%**} & \multicolumn{2}{c}{**W, 60 vol\%**} \\ \hline
**L-Power** & **Ex.-Speed** & **L-Power** & **Ex.-Speed** & **L.-Power** & **Ex.-Speed** \\ \hline
**155 W** & **1200 mm/s** & **155 W** & **1200 mm/s** & **155 W** & **1200 mm/s** \\
170 W & 1320 mm/s & 170 W & 1320 mm/s & 170 W & 1320 mm/s \\
140 W & 1320 mm/s & 140 W & 1320 mm/s & 140 W & 1320 mm/s \\
170 W & 1080 mm/s & 170 W & 1080 mm/s & 170 W & 1080 mm/s \\
140 W & 1080 mm/s & 140 W & 1080 mm/s & 140 W & 1080 mm/s \\ \hline \multicolumn{2}{c}{**W, 60 vol\% + heating**} & \multicolumn{2}{c}{**W, 70 vol\% + heating**} & \multicolumn{2}{c}{**W, 60 vol\% 2 nd**} \\ \multicolumn{2}{c}{**Adaption**} \\ \hline
**L-Power** & **Ex.-Speed** & **L-Power** & **Ex.-Speed** & **L.-Power** & **Ex.-Speed** \\ \hline
**115 W** & **750 mm/s** & **115 W** & **750 mm/s** & **100 W** & **450 mm/s** \\
130 W & 1000 mm/s & 130 W & 1000 mm/s & 110 W & 500 mm/s \\
100 W & 1000 mm/s & 100 W & 1000 mm/s & 90 W & 500 mm/s \\
130 W & 500 mm/s & 130 W & 500 mm/s & 110 W & 400 mm/s \\
100 W & 500 mm/s & 100 W & 500 mm/s & 90 W & 400 mm/s \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Experimental plans for the development of suitable process parameters. Hatching distance is set constant. Central points are fabricated three times and are marked in bold font. Each experimental run is executed fully randomized. Figure 1 presents the measured Archimedean density in comparison to the theoretical value. With an increase in tungsten content from 40 to 50 and 60 vol% (black data points), a descending trend in density was observed. This behavior can be explained by the fact that the tungsten particles had an influence on process-relevant properties such as thermal conductivity or absorptivity of the laser energy. Therefore, the boundary conditions in the powder bed changed.