| Abstract Scope |
Laser powder bed fusion (LPBF) is the most extensively used metal additive manufacturing technology, owing to its unique capabilities for building parts with high geometry complexity and fine features. In a LPBF process, sparks (i.e. spattered particles) can be observed to follow the laser scanning path, indicating the existence of high-velocity vapor arising from the melt pool. Indeed, strong metal vaporization occurs in LBPF, and the resulting recoil pressure can create a deep vapor depression in the melt pool, which is often referred to as keyhole. Keyhole is a critical dynamic structure feature in LPBF. Here, I will present the direct observation of keyhole dynamics using high-speed high-resolution synchrotron x-ray imaging. Based on the morphology and fluctuation mode, keyholes can be categorized as stable and unstable types. Their effects on the effective laser absorption, melt pool morphology development, and generation of various structure defects will be elucidated. |