# Mechanical Properties of White Metal on SCM440 Alloy Steel by Laser Cladding Treatment
## 3 Results and Discussion
### SEM Microstructure Analysis and EDS Analysis  
In the case of the white metal produced by the centrifugal casting method, no HAZ was observed at the interface with the substrate, as shown in Figure 5, which was consistent with the hardness data presented above. Table 3 outlines the EDS-analyzed chemical composition of the boundary layer and white metal cladding layer. As shown therein, Sn occupied the highest proportion. Figure 6 presents SEM images of the laser cladding layers with the laser power. As shown in Figure 6a, an uneven HAZ was formed at the interface between the SCM440 alloy steel substrate and the white metal at a laser power of 1.1 kW. Moreover, power particles could not be mounted properly during the cladding because of insufficient melting. In the case of 1.5 kW, a relatively uniform HAZ of about 81.0 \(\upmu\)m formed, presumably owing to the strong adhesion between the substrate and the white metal. However, Figure 6c indicates that more substrate components were mixed into the white metal layer as a result of excessive energy output from the 1.5 kW laser during white metal mounting. As demonstrated in the EDS analysis graphs in Figure 7, representing the components of such a mixed layer, the proportion of Fe in the white metal layer increased from 1.39% at 1.1 kW to 75.06% at 1.5 kW, while Sn, a major component of wh  
Figure 5: SEM image of the centrifugal casting-type white metal. Figure 6: SEM images of the laser cladding at laser powers of (**a**) 1.1 kW, (**b**) 1.3 kW and (**c**) 1.5 kW. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Element** & **a (wt.\%)** & **b (wt.\%)** \\ \hline Si & 0.51 & 0 \\ Fe & 10.96 & 0.81 \\ Cu & 12.31 & 39.95 \\ Sn & 71.44 & 56.53 \\ Sb & 4.77 & 2.7 \\ Total & 100 & 100 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Chemical composition of the centrifugal casting specimen at the (**a**) boundary layer and (**b**) additive manufacturing layer. (spot a. b.). decreased from 95.74% to 19.01%. In the HAZ (Figure 7b), Fe increased from 53.98% to 90.02%, and Sn decreased from 35.14% to 5.71%. These results are consistent with the measurement results plotted in Figure 2, indicating that the hardness of the cladding layer in the 0.1 mm section increased with the laser power because of the dispersion of Fe in the substrate into the cladding layer. As a result of SEM and EDS analysis, according to the laser power, the higher and wider HAZ layer was formed as the laser power increased, and the composition analysis of the cladding layer showed that the Fe (base material) ratio increased and the Sn (white metal) ratio decreased. During the white metal lamination, the amount of heat input was increased, and the inner part of the base material was affected so that a layer in which the base material components were mixed up and the cladding layer was formed. Therefore, it can be seen that it is consistent with the result of increasing the micro Vickers hardness value shown in Figure 2. It is expected that the formation of the mixed layer will increase the wear of the shaft surface in contact with the bearing. Then, at a laser power of 1.3 kW, the microstructure changes with the powder feed rate and laser head speed were analyzed. According to the analysis results, a uniform HAZ with an average thickness of 32.8 \(\upmu\)m formed at a powder feed rate of 2.5 rpm (Figure 8a), whereas the HAZ exhibited an uneven morphology at a powder feed rate of 3.5 rpm (Figure 9b). The comparison of the HAZ morphology, depending on the laser head speed (10 mm/s vs. 20 mm/s), revealed that a uniform HAZ formed at a head speed of 10 mm/s, as shown in Figure 10. The EDS analysis of each condition revealed that the Fe decreased and Sn (major component) increased as the powder feed rate increased or the head speed decreased, as shown by the graphs in Figures 9 and 11, respectively. Figure 7: Comparison of energy-dispersive X-ray spectroscopy (EDS) results with the laser power of the laser cladding at (**a**) the cladding layer and (**b**) the heat-affected zone (HAZ) layer.