Influence of laser power and scanning speed on necking growth of SS316L powder in laser melting processes

Necking is a crucial phenomenon that can highly affect the mechanical properties and structural integrity of the material, especially in additive manufacturing. To understand the effect of laser power and scanning speed on necking formation between powder particles for SS316L, a study was conducted on the joining of powder particles under various laser parameters. This knowledge is valuable for fine-tuning laser processing parameters across various industrial applications. For this study, Uniweld Laser 3000 was used for the laser joining process. For the laser parameters, laser speeds ranging from 50 mm/s to 150 mm/s and laser powers of 15 W, 20 W, and 25 W were used in this study. The laser process was concentrated explicitly on observing the powder joining process within a single track. It was observed that the necking size increases as the laser power increases and the scanning speed decreases. At 150 mm/s with 150 W, no particle joining was observed as the powder absorbed insufficient energy to undergo the melting process. At different laser powers, the necking growth rate between scanning speeds varies. When laser power was 15 W and scanning speed was 125 mm/s, the neck size increased to 49 µm. The necking increases further to 62 µm, 93 µm, and 100 µm when the scanning speed is reduced to 100 mm/s, 75 mm/s, and 50 mm/s. The same trend can also be observed under higher laser power, but at a different neck growth rate. Analysis of dislocation density for different laser parameters was also performed. It has been found that the highest energy density corresponds to the highest dislocation density, with a value of 2.03×1014 m-2. It can be concluded that a slower scanning speed allows particles to absorb more heat for the melting process, hence increasing the necking size of the particles.