Qualitative analysis of potential pore healing phenomenon in L-PBF using operando high speed X-ray imaging

Abstract

A major source of flaws and defects in Laser Powder Bed Fusion stems from the creation of pores during the build process. In-process mechanisms that produce pores, such as keyholing and lack of fusion, and secondary processes that can reduce porosity, such as hot isostatic pressing, have been extensively studied. Many of these works also suggest that if pores are detectable then it could be possible to develop a schema to “heal” the defects in-situ. However, the effects of a subsequent laser pass on pores generated in prior layers have not been fully studied due to the experimental difficulties. It is therefore important to understand if these interaction mechanisms have the potential to “heal” and enable control methods that select laser parameters to target areas of suspected porosity. This paper identifies and qualitatively analyzes pore healing mechanisms in L-PBF using high speed X-ray imaging. Several key phenomena affecting keyhole and melt pool interactions with existing pores are identified in the X-ray images and the effects of these phenomena are discussed. Finally, several areas for future work are presented, including the need for robust quantitative analysis of these phenomena.