Abstract
Laser-powder interaction and meltpool dynamics govern the physics behind the selective laser melting process. Spattering is an unavoidable phenomenon taking place during the process which results in reconstituted particles falling within the powder bed. These are known to influence the interaction between the incident laser beam and the powder. These particles can consequently have a negative effect on final part integrity and quality of recycled powder. Hence, it is crucial to assess the characteristics of spatter particles to avoid the printing of defective parts. This work reports a detailed characterisation of spatter matter generated during the selective laser melting of stainless steel. To better assess the characteristics of the spatter, the spattered material was benchmarked against the virgin powder. The results showed no significant variation between the virgin and spattered particles in terms of the bulk material crystal structure. However, the spatter particles’ morphological, surface chemical, optical and physical properties assessed do differ significantly from those of the virgin powder. The results presented in this work are of significant contribution to the powder bed fusion field of additive manufacturing as they provide a unique insight to the characteristics of spatter matter generated from the processing of 316L stainless steel powder.
Highlights
In additive manufacturing, several types of metal powders are used in the manufacturing of engineered parts
The results presented in this work are of significant contribution to the powder bed fusion field of additive manufacturing as it provides a unique insight to the characteristics of spatter matter generated from the processing of 316L stainless steel powder
The powder bulk and surface chemical composition was investigated using energy dispersive X-ray (EDX) analysis coupled into a Hitachi S5500 Field Emission scanning electron microscope (SEM) and the X-ray photoelectron spectroscopy (XPS) was carried out using a conventional Mg Kα X-ray source in conjunction with a VG Microtech electron energy analyzer operating at a pass energy of 20 eV and at a pressure of 1x10-9 mbar, yielding an overall resolution of 1.2Ev
Summary
Several types of metal powders are used in the manufacturing of engineered parts. The spattering phenomenon is unavoidable and the deposition of the spattered matter in the consecutive layers can lead to the presence of pores, voids and other defects in printed parts [27] This can be explained by the larger, partially welded and satellite powder particles formed during the molten metal ejection. Other studies [33,34,35,36] used mathematical models, such as finite element analysis, simulations and high-speed cameras to validate experimental results These investigations reported that the ejected powder particles are highly affected by the laser power applied, the scanning speed and the amount of metal vapour and plasma formed above the meltpool. The metal powders under study were collected from the as-supplied powder container (virgin powder), around the printed part and near the argon gas outlet (spattered powder) and from the powder overflow container (recycling powder)
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