Examining the Quality of New and Reused Powder in the Powder Bed Fusion Process via Optical Microscopy

The quality of the powder used in Laser-based Powder Bed Fusion (L-PBF) additive manufacturing processes plays a key role in the properties of the fabricated part. The particle size distribution (PSD) and morphology of the powder particles affects the flowability of the powder and can adversely affect the quality of the final part. Ti6Al4V powder for additive manufacturing processes is relatively expensive, making L-PBF a costly process. One method of reducing the associated costs by making the process more sustainable is to reuse unconsolidated powder from the breakout step of a prior build for subsequent part builds. However, reused powder will have been exposed to the environment of the L-PBF build chamber and spatter particles from the L-PBF melt pool leads to the formation of partially-melted and agglomerated particles. Composition assessment of the powder quality is required between powder re-use cycles to ensure it remains within specification for subsequent part builds, however, the Inert Gas Fusion method used for detecting interstitial elements at these very low composition thresholds is not typically available at the manufacturing premises. Industry, therefore, requires an effective and low-cost proxy method of assessing powder quality. Two different sample preparation techniques are used in this investigation to obtain digital images of Ti6Al4V powder in the virgin state and of the sieve-captured powders after seven reuse cycles. This paper provides an overview of changes in powder properties between virgin powder and the sieve-captured powders after seven reuses. A discussion of the advantages and limitations of both powder preparation and imaging techniques is provided. It is proposed that the development of optical-based image analysis techniques can be used to get a reasonable classification of powder quality for the L-PBF process.