Critical instability at moving keyhole tip generates porosity in laser melting
Critical instability at moving keyhole tip generates porosity in laser melting
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DOI：
10.1126/science.abd1587
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发表时间：
2020-11-27
期刊：
影响因子：
56.9
通讯作者：
Sun, Tao
中科院分区：
文献类型：
--
作者：
Zhao, Cang;Parab, Niranjan D.;Sun, Tao
激光粉末床融合是一种占主导地位的金属3D打印技术。然而，对于疲劳敏感的应用，孔隙缺陷仍然是一个挑战。一些孔隙与深而窄的蒸汽凹陷（称为小孔）相关，其在高功率、低扫描速度的激光熔化条件下发生。利用高速X射线成像技术，可以对小孔尖端临界失稳引起的Ti-6Al-4V中孔隙的详细形成过程进行操作性观察。我们发现，在功率速度空间中的小孔孔隙率制度的边界是尖锐和光滑的，只有轻微的变化之间的裸板和粉末床。临界小孔不稳定性在熔池中产生声波，该声波为小孔尖端附近的孔隙提供额外的但重要的驱动力，以远离小孔移动并被捕获为缺陷。
Laser powder bed fusion is a dominant metal 3D printing technology. However, porosity defects remain a challenge for fatigue-sensitive applications. Some porosity is associated with deep and narrow vapor depressions called keyholes, which occur under high-power, low-scan speed laser melting conditions. High-speed x-ray imaging enables operando observation of the detailed formation process of pores in Ti-6Al-4V caused by a critical instability at the keyhole tip. We found that the boundary of the keyhole porosity regime in power-velocity space is sharp and smooth, varying only slightly between the bare plate and powder bed. The critical keyhole instability generates acoustic waves in the melt pool that provide additional yet vital driving force for the pores near the keyhole tip to move away from the keyhole and become trapped as defects.