## 3 Results and Discussion
### Mixing Behavior in Laser-Arc Hybrid Test Welds  
As noted earlier, conventional dilution calculations based on the weld cross-sectional area are not always suitable for thicker weld cross-sections, which motivated more detailed examination of the mixing of the filler metal in the test welds. Mixing in the vertical direction from the weld surface to the root and the uniformity of the mixing, that is, how homogenously the filler metal is distributed across the whole weld cross-section, were of particular interest. EDS mapping and stepwise line characterization were used to reveal possible differences in chromium distribution between the over-alloyed filler metal and base metal. Figure 9 shows EDS mapping results for the laser-arc hybrid test welds. The images show chromium distribution in weight-% for each test weld cross-section. The chromium distribution is visualized using colour contouring. Greenish colours present the chromium weight-% content level of the base metal and dark red shows chromium weight-% content close to that of the filler metal. Yellow and orange colours are chromium weight-% content levels between these extremes. The mixing results from EDS stepwise characterization are presented as transversal filler metal mixing profiles \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Weld** & **Melted Base** & **Melted Filter** & **Weld Metal** & **Base Metal** & **Filler Metal** \\
**Identification** & **Metal Area [mm\({}^{2}\)]** & **Metal [mm\({}^{2}\)]** & **Area [mm\({}^{2}\)]** & **Dilution [\%]** & **Portion [\%]** \\ \hline LAH1 & 19.5 & 5.1 & 24.6 & 79 & 21 \\ LAH2 & 25.8 & 5.4 & 31.2 & 83 & 17 \\ LAH3 & 16.7 & 8.2 & 24.9 & 67 & 33 \\ LAH4 & 19.9 & 8.6 & 28.5 & 70 & 30 \\ LAH5 & 17.1 & 9.3 & 26.4 & 65 & 35 \\ LAH6 & 19.5 & 9.9 & 29.4 & 66 & 34 \\ \hline LCW1 & 14.2 & 3.1 & 17.3 & 82 & 18 \\ LCW2 & 15.1 & 4.1 & 19.2 & 79 & 21 \\ LCW3 & 13.5 & 5.2 & 18.7 & 72 & 28 \\ LCW4 & 12.3 & 5.1 & 17.4 & 71 & 29 \\ LCW5 & 16.2 & 8.2 & 24.4 & 66 & 34 \\ LCW6 & 17.1 & 8.6 & 25.7 & 67 & 33 \\ LCW7 & 8.6 & 11.3 & 19.9 & 43 & 57 \\ LCW8 & 9.0 & 10.2 & 19.2 & 47 & 53 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Summary of cross-sectional areas of laser arc-hybrid (LAH) and laser cold-wire (LCW) test welds. Welding energy input values per weld length [kJ/mm]: LAH1&2 = 0.57; LAH3&4 = 0.77; LAH5&6 = 0.64; LCW1-6 = 0.55; LCW7&8 = 0.46. (measurement lines 1 to 4) calculated according to Equation (1). Figure 10 presents tabular data for average values of filler metal mixing determined at the measurement lines ML1-ML4 of the laser-arc hybrid test welds. The images in Figure 9 show a clear difference in filler metal mixing between the weld surface part (upper half) and the weld root part (lower half) of the weld cross-sections of the I-groove weld with 0.4 mm root gap (Figure 9a,b). The same behaviour can be seen for both leading and trailing filler wire feeding. More reddish colour contouring indicates that more intensive mixing has occurred on the weld surface with leading wire feeding; on the other hand, trailing wire feeding seems to have provided slightly better mixing from the weld midsection towards the weld root. Figure 10 shows that the average filler metal mixing-% values of test welds LAH1 and LAH2 are around 38% and 31-34% for the upper half of weld cross-section and \(\sim\)26% and \(\sim\)25-28% for the lower half, respectively. Figure 9: Energy dispersive spectroscopy (EDS) mapping images (**a–f**) showing the distribution of chromium in laser arc-hybrid test welds. When the root gap is widened from 0.4 mm to 0.8 mm, mixing becomes noticeably better throughout the weld cross-section. The results of both leading and trailing wire feeding with 0.8 mm root gap (Figure 9c,d) show enhanced mixing behaviour across the whole weld cross-section in terms of higher chromium contents and enhanced distribution. The use of trailing wire feeding (Figure 9d) shows slightly better mixing at the weld root portion than leading wire feeding (Figure 9c).