Gas-atomized powders are commonly used in additive manufacturing, specifically laser powder bed fusion, due to their high flowability during recoating. Morphological changes can occur in particles that are irradiated by the laser during additive manufacturing, but are not incorporated into the melt pool. These irradiated particles will affect the rheology of the recycled powder in subsequent builds, potentially leading to failures due to uneven powder flow or spatial distribution. Thus, a better understanding of mechanisms that degrade the sphericity of powder after being laser irradiated is needed. This research examines morphological changes in Al and Al-Cu eutectic powders after laser melting. Two complementary approaches were taken. First, particles found along the edges of line scans following high-power (300 W) laser irradiation were characterized. The collected particles displayed morphological anomalies not observed in the as-received powder. Then, to gain a more quantitative and controlled perspective on morphological evolution, the same base powders were dispersed onto glass substrates and irradiated with a low-power (6.5 W) CW laser diode. This approach, which permits characterization of specific particles before and after laser irradiation, clearly shows laser-induced changes in the surface morphology of particles in the form of dents and rifts. These results suggest that isolated melting and resolidification of particles contained within their respective oxide shells can occur at the relatively low laser energy densities present at the edges of laser melt tracks. Thermal stresses developing in the oxide shell during cooling can account for the observed morphological changes in the context of shell-buckling theory.

中文翻译：

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激光熔化后Al和Al-Cu粉末的形貌变化

气体雾化粉末通常用于增材制造，特别是激光粉末床融合，因为它们在重涂过程中具有高流动性。在增材制造过程中，激光照射的颗粒可能会发生形态变化，但不会并入熔池。这些受辐照的颗粒会影响后续构建中回收粉末的流变性，可能会由于粉末流动或空间分布不均匀而导致故障。因此，需要更好地了解激光照射后降低粉末球形度的机制。本研究考察了激光熔化后 Al 和 Al-Cu 共晶粉末的形态变化。采取了两种互补的方法。第一的，对在高功率 (300 W) 激光照射后沿线扫描边缘发现的颗粒进行了表征。收集的颗粒显示出在原样粉末中未观察到的形态异常。然后，为了获得关于形态演变的更定量和可控的视角，将相同的基础粉末分散到玻璃基板上，并用低功率 (6.5 W) 连续激光二极管进行照射。这种方法允许在激光照射之前和之后表征特定颗粒，清楚地显示了激光诱导的颗粒表面形态的变化，以凹痕和裂缝的形式存在。这些结果表明，在激光熔化轨迹边缘存在的相对较低的激光能量密度下，包含在它们各自的氧化物壳中的颗粒会发生孤立的熔化和再凝固。