Abstract
We employ the high-speed synchrotron hard X-ray imaging and diffraction techniques to monitor the laser powder bed fusion (LPBF) process of Ti-6Al-4V in situ and in real time. We demonstrate that many scientifically and technologically significant phenomena in LPBF, including melt pool dynamics, powder ejection, rapid solidification, and phase transformation, can be probed with unprecedented spatial and temporal resolutions. In particular, the keyhole pore formation is experimentally revealed with high spatial and temporal resolutions. The solidification rate is quantitatively measured, and the slowly decrease in solidification rate during the relatively steady state could be a manifestation of the recalescence phenomenon. The high-speed diffraction enables a reasonable estimation of the cooling rate and phase transformation rate, and the diffusionless transformation from β to α’ phase is evident. The data present here will facilitate the understanding of dynamics and kinetics in metal LPBF process, and the experiment platform established will undoubtedly become a new paradigm for future research and development of metal additive manufacturing.
Highlights
Additive manufacturing (AM, a.k.a. 3D printing) of metallic materials has been witnessing tremendous growth over the past three decades[1,2,3,4,5], in the fields of medical, aerospace, automobile, and defense industries[6, 7]
Most of the metal AM systems are of the laser powder bed fusion (LPBF) type owing to its superior capability to make geometrically complex parts[8, 9]
It is demonstrated that quantitative structural information on melt pool size/shape, powder ejection, solidification, and phase transformation can be obtained from the high-resolution time-resolved X-ray images and diffraction patterns
Summary
Additive manufacturing (AM, a.k.a. 3D printing) of metallic materials has been witnessing tremendous growth over the past three decades[1,2,3,4,5], in the fields of medical, aerospace, automobile, and defense industries[6, 7]. In a typical LPBF process, a laser beam scans across a thin layer of metallic powders, and locally melts the powders through to the layer below[10, 11]. It is extremely challenging to experimentally characterize the dynamics of the LPBF process due to the highly localized and very fast interaction of the laser beam with metal powders. We report in situ probing the dynamics of the LPBF process inside as well as above the surface of the powder bed using high-speed hard X-ray imaging and diffraction techniques at the Advanced Photon Source (APS). It is demonstrated that quantitative structural information on melt pool size/shape, powder ejection, solidification, and phase transformation can be obtained from the high-resolution time-resolved X-ray images and diffraction patterns. The experimental and data analysis approaches developed here will provide a compass pointing to the fundamental understanding of the physics in the AM process, and will further accelerate the coming of the AM age
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