In this work, the mechanism of melt pool oxidation and reduction during the powder bed fusion was studied. To elucidate the mechanism, the effect of process parameters such as laser power, scan speed and shield gas flow speed on the variation on oxygen, nitrogen and carbon content in the printed material was investigated. In 316L stainless steel, melt pool reduction and oxidation occurred simultaneously during the process involving CO and CO₂ gas evaporation at the depression zone. An increment of energy density and shield gas flow speed led to an increase in melt pool reduction rate and a decrease in porosity. It was found that nitrogen and CO gas could be a major constituent of vapor when oxygen and nitrogen content in the powder was high. Uneven solidification texture and melt pool instability were observed when the speed of shield gas flow was similar to the laser scan speed. Porosity, melt pool dimension, and solidification texture also changed under different shield gas flow speeds. Higher oxygen content and porosity was found in bi-directional scanning pattern than in uni-directional scanning pattern. Among uni-directional scanning pattern cases, scanning along the flow direction resulted in higher oxygen content and porosity compared to opposite and perpendicular scanning. Interaction between shield gas flow and laser plume was appreciably engaged in melt pool oxidation and reduction rate.

在这项工作中，研究了粉末床熔融过程中熔池氧化和还原的机理。为了阐明机理，研究了诸如激光功率，扫描速度和保护气体流速等工艺参数对印刷材料中氧，氮和碳含量变化的影响。在316L不锈钢中，涉及CO和CO ₂的过程中熔池还原和氧化同时发生凹陷区的气体蒸发。能量密度和保护气体流速的增加导致熔池还原速率的增加和孔隙率的降低。发现当粉末中的氧气和氮气含量高时，氮气和一氧化碳气体可能是蒸气的主要成分。当保护气体的流动速度与激光扫描速度相似时，观察到不均匀的凝固组织和熔池不稳定性。在不同的保护气体流速下，孔隙率，熔池尺寸和凝固组织也发生了变化。在双向扫描模式中发现比单向扫描模式中更高的氧含量和孔隙率。在单向扫描模式的情况下，与反向和垂直扫描相比，沿流向扫描会导致较高的氧含量和孔隙率。