## 3 Results
The electronic thermal conductivities in the cross-plane and in-plane direction are comparable,  
Figure 3: Dependence of CM247 LC density on energy density. but the lattice thermal conductivity is higher in the in-plane direction. The speed of sound, \(\
u\), in Equation (2) can be expressed as follows:  
\[v=\sqrt{\frac{E}{\rho}} \tag{3}\]  
The speed of sound of the lattice thermal conductivity shown in Equation (2) is the square root of the ratio of the elastic modulus (GPa), \(E\), and density (kg/m\({}^{3}\)), \(\rho\), as shown in Equation (3). Samples manufactured by SLM with metallic powder have a higher elastic modulus in the in-plane direction compared with the cross-plane direction [11]. In the manufacturing process, thermal stress accumulates as a result of rapid heating and cooling [34], or flat pores are generated because of the low energy density [35; 36] between layers. These defects result in a higher elastic modulus in the in-plane direction than in the cross-plane direction [11; 14]. The anisotropy according to direction varies depending on the porosity, but the in-plane direction has an elastic modulus that is approximately 50% higher than that in the cross-plane direction [11]. Therefore, the thermal conductivity is higher in the in-plane direction because it is proportional to the square root of the elastic modulus. To analyze the change in thermal conductivity caused by the difference in density, the microstructure of the cross-section was observed. Figure 6a-d show cross-plane and in-plane OM images of high- and low-density samples. Figure 6a,b show the cross-plane and in-plane cross-sections from a high-density sample fabricated with a laser power of 150 W, 1200 mm/s scan speed, and 20 um layer thickness. Figure 6c,d show the cross-plane and in-plane cross-sections from a low-density sample fabricated with a laser power of 100 W, 1800 mm/s scan speed, and 30 um layer thickness. It can be seen that the difference in density reflects the influence of defects and pores generated inside the material. Defects and pores can be classified into three groups: pores, melting-related defects, and cracks [37]. In Figure 6, blue circles indicate that unmelted particles are present in large pores. This is because the particles did not melt, as the low laser power could not supply sufficient heat. These pores are formed because of the low energy density [35]. The black dotted line in Figure 6d represents the process of generating irregular-shaped pores. The mechanism of irregular pore generation is shown in a schematic diagram in Figure 6e. Gas is trapped in the pores during manufacturing. Irregular pores are formed between the layers because of the gas contraction force and gravity during rapid heating and cooling [36]. The ellipsoid  
Figure 4: Dependence of cross-plane and in-plane electronic and lattice thermal conductivities on temperature. pores expand because of the high gas temperature. As the temperature decreases, the gas in the pores contracts, leading to the formation of flat pores as a result of gravity. Therefore, the pores have a flat shape in the in-plane direction. Furthermore, the pores marked with red circles in Figure 6 are the result of an incomplete melting process. The pores can reduce the density, but they also interfere with grain growth. As shown in Figure 6d, the grain growth is limited by the presence of pores, and thus the grains are smaller than those shown in Figure 6b. Figure 5: (**a**) Dependence of thermal conductivity in the cross-plane and in-plane directions on density and (**b**) electronic and lattice contributions to cross-plane and in-plane thermal conductivities.