## 4 Results Analysis and Discussion
### Analysis of Simulation Results for Single-Layer Multi-Channel Deposition  
Simulation calculations of single-layer multi-channel laser deposition with one-way parallel scanning were performed using double-channel overlapping process parameters, i.e., a powder feeding rate of 12.0 g/min, laser power of 500 W, scanning speed of 10 mm/s, and overlapping rate of 30%. Figure 17 depicts the structure of the deposition as a function of time, revealing the formation of an overlapping deposition with favorable surface morphology as the processing continued. Figure 18 depicts the fluctuation of surface temperature field distribution with time. Comparing the four plots of (a), (b), (c), and (d), we can see that the distance between isotherms in the left area of the current overlapping deposition channel, i.e., near the side of the previous overlapping deposition channel, is significantly greater than that on the other side, whereas the temperature gradient is smaller.  
Figure 16: The temperature change on the symmetry line of the first deposition surface.  
To better analyze the temperature characteristics of the single-layer multi-channel and the interaction between the overlapping deposition channels, an observation point is chosen at a distance of 3 mm from the commencement of the scan along the scan path of the first deposition channel on the surface of the substrate., as depicted in Figure 19, and the temperature variation of the grid at this location with time was recorded, as depicted in Figure 20.  
Figure 17: Variation of the shape of deposited layer with time for single layer multi-laser processing. (a) 0.6 s; (b) 1.2 s; (c)1.8 s; (d) 2.4 s.  
Figure 18: Variation of temperature field with time for single-layer multi-laser processing. (a) 0.6 s; (b) 1.2 s; (c)1.8 s; (d) 2.4 s.  
Figure 20 demonstrates that (1) Throughout the first deposition channel scan from 0 s to 0.6 s, the laser head is exactly above the observation point at 0.3 s, when the observation point's temperature reaches its peak, until the completion of the first deposition channel scan at 0.6 s. (2) At the start of the second deposition channel scan, the temperature of the observation point is still falling. However, as the spot approaches, the temperature of the observation point begins to climb, and the amplitude of the temperature recovery is exactly between 200 K and 300 K. (3) In the second scan, there is a slight lag in the moment of temperature extremes at the observation point relative to the moment when the spot position is side-by-side with the observation point, and this feature appears again in the third scan, but the lag is more pronounced than in the second scan because the spot position is further away from the observation point position. (4) During the third scan, the temperature change at the observation point continued to follow a drop-rise-drop pattern, but the temperature return was significantly smaller than it was in the second scan, indicating that the temperature effect on the first deposition layer was significantly smaller in the third scan than in the second. (5) During the last 1.8 s-2.4 s, i.e., the fourth scan, the temperature at the location of the scan point has stopped rising and has been in a cooling state, but has slowed down its cooling. (6) The rewarming process in the first deposition channel maintains the temperature above about 1000 K for a longer length of time, influencing the phase composition of IN718 alloy material after solidification.  
Figure 19: Schematic diagram of the location of the observation point.  
Figure 20: Temperature variation curve with time at the location of the observation point.