A versatile miniature laser powder bed fusion setup for in situ observations of keyhole and phase transformation dynamics via high-speed synchrotron imaging and diffraction

Laser powder bed fusion (LPBF) additive manufacturing (AM) enables to three-dimensionally print intricate and customized high-end parts with a great promise for rapid manufacturing applications in aerospace, automobile, and medical industries. However, due to the lack of direct observations of defect formation and phase transformation dynamics, it suffers from keyhole pore residuals and heterogeneous phase structure as a result of repeated heating and cooling, which cause safety concerns and hinder wide industrial adoption. Here, we develop a miniature LPBF (mini-LPBF) setup that is flexible for in situ observations of keyhole and phase transformation dynamics through high-speed x-ray imaging and diffraction when implemented at synchrotron beamlines. The experimental validations of this mini-LPBF setup with an exemplary FeCoNiCrMn high-entropy alloy are carried out at BL16U2 and BL12SW beamlines of the Shanghai Synchrotron Radiation Facility. The subsurface transient dynamics of keyhole and phase transformation are characterized down to melt pool scale: keyhole geometry and its fluctuation induced pore formation are captured in high temporospatial resolution by high-speed imaging; phase transition from face-centered cubic, fully liquid and back to crystalline structures is quantified by time-resolved high-energy diffraction. This mini-LPBF setup provides the powerful infrastructure for keyhole fluctuation induced defect formation and phase transformation dynamics studies and experimental inputs for high-fidelity modeling. The knowledge gained by the aid of mini-LPBF setup through in situ monitoring of laser-metal interaction will improve the process stability and phase engineering for metal AM of novel alloys.