Qualification of laser powder bed fusion processed 17-4 PH stainless steel as a function of powder condition

Abstract

The metal additive manufacturing process of laser powder-bed fusion (LPBF) presents a challenge to develop qualified processes to match the rapid pace of technology development. An aspect of the LPBF process where this applies is defining the how powder feedstock conditions affect the quality of produced components. This study examines how in-machine powder feedstock supplies evolve and are otherwise affected during the LPBF process, and how these effects impact subsequent builds which use said feedstock. An examination of powder flowability, rheology, and morphology is conducted to characterize the powder conditions. To study the effects, an assessment of produced component tensile, fatigue, and microstructural properties is conducted. Fatigue life is analyzed using a reliability modeling approach in order to provide detailed statistical conclusions often missing in other analyses. Powders are found to evolve their characteristics over exposure to repeated LPBF processes, particularly in the extremes of powder size distribution and measures of bulk flow. No significant effects on microstructural, hardness, tensile, and fatigue properties of the produced components are shown. Fatigue life is discovered to exhibit a dependence on spatial origin of the produced component. Additionally, a detailed characterization of the scatter in fatigue life typical to the process and material is provided.