# Numerical and Experimental Investigations of Laser Metal Deposition (LMD) Using STS 316L
## 4 Results and Discussion
G x R, G, and R tend to decrease as the location moves from bottom to top. Further, the decrease in slope between the middle and the top was smaller than that between the bottom and the middle. This means that during deposition, a significant portion of the heat input supplied by the laser heat source is rapidly transferred to the base material, and the difference between the decreasing slopes of each solidification parameter reflects the effect of heat accumulation for each layer of the deposit due to repeated heat input. As shown in Figure 5b, G x R was in the range of \(1\times 10^{3}\) to \(2.5\times 10^{3}\)\({}^{\circ}\)C/s, which agrees with the results of other studies [15; 27; 28]. As shown in Figure 6, cross sections of the deposit were analyzed using an optical microscope to investigate the relationship between the calculated solidification parameters and the formed microstructure. Figure 6a-c shows the microstructures at the bottom, middle, and top regions of the deposit for 0-s interlayer time. A cellular structure was observed in the three figures; however, a small amount of cellular dendrite was additionally observed in the top region in Figure 6c. This is because G/R decreases from the bottom to the top area, as shown in Figure 5. This phenomenon was also observed in different locations of the deposit, as shown in Figure 6d-f. These results suggest the possibility of quantifying the conditions for morphology change between cellular and cellular dendrite. In addition, Figure 6 clearly shows that the size of the cell gradually increases from the bottom (a, d) to the top (c, f) owing to the effect of the cooling rate described in Figure 5.  
Figure 5: Solidification parameter measurement position and results; (**a**) Schematic diagram of solidification parameter measurement position; (**b**) behavior of solidification parameters and cooling rate at each position. Figure 7 shows the calculated G/R values for the deposit. The G/R value gradually decreases from the bottom to the top of the deposit. This trend was consistent with the trends of G, R, and G \(\times\) R as shown in Figure 4b. G/R has the same order of magnitude of 102 \({}^{\circ}\)C\(\cdot\)s/mm\({}^{2}\) for the bottom, middle, and top positions. However, other researchers reported that the G/R values of STS 316L deposits with cellular appearance in the deposit were of the order of 102 \({}^{\circ}\)C\(\cdot\)s/mm\({}^{2}\)[12] or 102-103 \({}^{\circ}\)C\(\cdot\)s/mm\({}^{2}\)[15]. In addition, the G/R value for planar and equiaxed appearance in STS 316L deposits is \(\sim\)5 \(\times\) 104 \({}^{\circ}\)C\(\cdot\)s/mm\({}^{2}\)[12] or higher and \(\sim\)10 \({}^{\circ}\)C\(\cdot\)s/mm\({}^{2}\)[29] or lower, respectively. In summary, planar and equiaxed formations were not expected to appear in the bottom, middle, or top of the deposits investigated in this study. Therefore, it can be concluded that the microstructure observed in Figure 6 was formed with the G/R values shown in Figure 7. Finally, by combining Figures 5-7, the relationship between G/R and the microstructure characteristics can be derived as follows:  
\[498\ (cellular\ dendrite)\leq G/R\leq 598\ (cellular) \tag{4}\]  
Figure 6: Optical microscope image of microstructure at each position of the deposit: (**a–c**) microstructure at the bottom, middle, and top of the deposit for 0-s interlayer time; (**d–f**) microstructure at the different bottom, middle, and top of the deposit for 0-s interlayer time. Figure 7: Behavior of G/R at each position in deposit.