PSI - Issue 69

Mohammadjavad Abdollahzadeh et al. / Procedia Structural Integrity 69 (2025) 2–19

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Fig.11: The development of melt pool, fluid flow, and heat transfer for the melting and solidification of the first track at a constant Y-Z cross section. From the figure it can be obtained that there are some porosities which are not filled and stayed at solidified single track. After t = 600 µs, the laser turned off in order to check the solidification process. The solidus temperature of NiTi is around 1555 (K), so the solidification process has been completed.

Figure 12 illustrates the temperature histories of six specific marker locations under laser parameters of 150 W power and a scan speed of 115 cm/s. The temperature trajectories at these points exhibit a consistent pattern, with a sharp initial increase followed by a gradual decrease. This rise in temperature is driven by the increasing energy input and absorption by the powder bed as the laser approaches each marker. The peak temperature significantly increases from approximately 2000 K to 5500 K as the laser progresses from the first to the last marker. Each marker reaches its peak temperature when the laser is directly overhead, marking the point of maximum energy absorption. As the laser moves, energy transfer between powder particles elevates the average temperature over time, leading to higher peak temperatures at subsequent markers. This trend continues until the melt pool achieves its maximum possible temperature, after which the peak temperature stabilizes. However, a slight reduction in peak temperature is observed at the final two markers, potentially due to their position within void cells containing gas phases, which can influence heat retention [60]. Another explanation, as suggested by Hu et al. [49] is that at the microscopic scale, the maximum temperature does not consistently align with liquid flow or convective heat exchange in the melt pool but instead oscillates within a defined range. Further insights are presented in Figure 13, which depicts the temperature histories of the six markers arranged vertically. The data clearly show that peak temperature decreases closer to the substrate, indicating that laser energy penetration diminishes at greater depths. This trend underscores the importance of understanding energy distribution within the melt pool for optimizing process parameters and ensuring consistent heat absorption throughout the material. These fluctuations in peak temperature and the associated thermal gradients can