Characterization of virgin and recycled 316L powder used in additive manufacturing

Paper in proceeding, 2016

Gas atomized 316L powder used in electron beam melting was investigated in virgin and recycled state to indicate the influence of recycling on the powder properties. A cross sectional investigation of the powder microstructure was performed by means of light optical microscopy and the phase composition was determined by means of X-ray diffraction analysis. The powder surface characterization was done by using X-ray photoelectron spectroscopy and high resolution scanning electron microscopy equipped with an energy dispersive X-ray analyser. Results showed that evenly distributed oxide particles in the submicron range can be observed on the surface of both virgin and recycled powder. The size of these oxide features on the surface of recycled powder is on average around 200 nm which is four times larger in comparison to virgin powder which is around 50 nm. The EDX analysis indicated enrichment of Si, Cr and Mn in the oxides. According to XPS, both powders are covered by homogenous Fe-oxide layer with particulate oxide features rich in Cr and Mn. Significantly higher amount of Cr oxide was detected on the surface of recycled powder compared to the surface of the virgin powder. The recycled powder also had lower Mn content on the surface. The reason for this is proposed to be the sublimation of Mn, which drives the decomposition of Mn-oxide. The powder cross-section showed that the microstructure of the recycled powder had a tendency to change towards cellular structure, while the microstructure of virgin powder is fully dendritic.