On the Morphology Changes of Al and Al-Cu Powder After Laser Melting
On the Morphology Changes of Al and Al-Cu Powder After Laser Melting
复制标题
DOI：
10.1007/s11663-020-01902-z
复制
发表时间：
2020-07
期刊：
影响因子：
--
通讯作者：
J. Skelton;C. V. Headley;E. Sullivan;J. Fitz-Gerald;J. Floro
中科院分区：
文献类型：
--
作者：
J. Skelton;C. V. Headley;E. Sullivan;J. Fitz-Gerald;J. Floro
气雾化粉末通常用于增材制造，特别是激光粉末床熔融，因为它们在重涂过程中具有高流动性。在增材制造过程中受激光照射但未纳入熔池的颗粒可能会发生形态变化。这些经过辐照的颗粒将影响后续构建中回收粉末的流变性，可能会因粉末流动或空间分布不均匀而导致失败。因此，需要更好地了解激光照射后粉末球形度降低的机制。本研究研究了激光熔化后铝和铝-铜共晶粉末的形态变化。采取了两种互补的方法。首先，对高功率（300 W）激光照射后沿线扫描边缘发现的颗粒进行了表征。收集到的颗粒表现出在收到的粉末中未观察到的形态异常。然后，为了获得对形态演变更加定量和可控的视角，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。这种方法可以在激光照射之前和之后对特定颗粒进行表征，清楚地显示激光引起的颗粒表面形态的变化（以凹痕和裂缝的形式）。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，可以发生包含在各自氧化物壳内的颗粒的孤立熔化和再凝固。冷却过程中氧化物壳中产生的热应力可以解释在壳屈曲理论的背景下观察到的形态变化。
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.