Determining processing behaviour of pure Cu in laser powder bed fusion using direct micro-calorimetry
Determining processing behaviour of pure Cu in laser powder bed fusion using direct micro-calorimetry
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DOI：
10.1016/j.jmatprotec.2021.117130
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发表时间：
2021-03-09
影响因子：
6.3
通讯作者：
Matthews, Manyalibo J.
中科院分区：
文献类型：
--
作者：
Gargalis, Leonidas;Ye, Jianchao;Matthews, Manyalibo J.
由于铜在普通红外激光二极管波长下的高反射率和高热导率，因此通过激光粉末床熔合（LPBF）来加工铜具有挑战性。以可预测和可重复的方式成功沉积铜依赖于了解小孔熔化机制的发展，以及在LPBF环境中与激光束相互作用时的加热、熔化、沸腾和蒸汽形成行为。在这项研究中，原位光学吸收率测量用于澄清激光材料相互作用的复杂物理。激光能量的吸收率使用直接微量热法测量，并与加工参数相关的熔池深度进行比较。对于100 μ m厚度的粉末，测得的吸收率比裸抛光盘的吸收率高约4倍。还表明，高于500 W的高激光功率和高达150 mm/s的扫描速度对于粉末层的有效熔化是合适的，这些参数克服了实现小孔熔化所需的阈值。这可以通过粉末颗粒内的多次反射和与裸盘相比填充粉末的较低导热率来解释。熔池的形成被认为是高度不稳定的，并观察到爆炸行为时，在小孔制度，吸收率值的高波动所造成的。这项工作表明，量热法可用于在加工过程中实时监测熔化行为，从而避免不必要的参数优化。此外，这里揭示的优化处理的参数窗口可以为未来的工作提供信息。
Copper is challenging to process by laser powder bed fusion (LPBF) given its high reflectivity at common infrared laser diode wavelengths and high thermal conductivity. Successful deposition of copper in a predictable and repeatable fashion relies on understanding the development of the keyhole melting regime, as well as heating, melting, boiling and vapour formation behaviour when interacting with a laser beam within an LPBF environment. In this study, in situ optical absorptivity measurements are used to clarify the complex physics of the laser material interaction. Absorptivity of laser energy is measured using direct micro-calorimetry and compared to melt pool depth in correlation to processing parameters. The measured absorptivity for a 100 mu m layer thickness of powder was found to be approximately four times higher than that of the bare polished discs. It was also shown that high laser power above 500 W and scan speed up to 150 mm/s are appropriate for effective melting of the powder layer, with these parameters overcoming the threshold required to achieve keyhole melting. This is explained by multiple reflections withing the powder particles and the lower thermal conductivity of packed powder in comparison to bare discs. Melt pool formation was found to be highly unstable and an explosive behavior was observed when in the keyhole regime, caused by high fluctuations in absorptivity values. This work demonstrates calorimetry can be used to monitor melting behaviour in a real-time fashion during processing for this challenging to proces material, thereby avoiding unnecessary parametric optimisation. In addition, the parametric window for optimum processing revealed here can inform future work.