Laser-matter interactions in additive manufacturing of stainless steel SS316L and 13-93 bioactive glass revealed by in situ X-ray imaging

The effect of powder oxidation on defect formation in laser additive manufacturing

“…A denoising algorithm, VBM3D [54], was applied, followed by background subtraction and segmentation. We quantified the spatter size and morphology, melt track geometry (e.g., length and depth), and internal porosity over time (see details in [7,8]). The spatter velocity was quantified using segmented images and an imageJ [55] plugin -TrackMate [56].…”

“…The newly formed molten pool then merges with the melt track. [7,8] The aforementioned track formation mechanisms are summarised as molten pool wetting [7,8] and vapour-driven powder entrainment [7,36].…”

“…It offers great promise in aerospace, nuclear fusion, and energy storage applications [2]; however, the uptake of LAM technologies in these areas has been hindered by inconsistent part performance. Specifically, the mechanical [3,4], thermal and electrical properties [5] of additive manufactured components have been lower than wrought components due to the accumulation of residual stresses [6] and the presence of defects, such as porosity [7,8], balling [9], and cracks [10].…”

“…Although there is a link between powder oxidation and defect formation, there are many hypotheses on the causes and formation of closed pores in AM, including 1) powder contamination [25], 2) coating defects [26,27], 3) the presence of carbon [28], hydrogen [29,30] and oxide inclusion [18] in the molten pool, 4) internal gas porosity from the powder [28,29,31], 5) keyhole collapse [32] and 6) gas entrapment during laser melting [33]. Furthermore, there are a few studies on the formation of irregular [8,18,28,34] and open pores [7,8,31]. Experiments are required to confirm the aforementioned mechanisms and to establish the conditions under which they are active.…”

Large scale selective laser melting : study of the effects and removal of spatter by the inert gas flow

“…A prediction model to detect the changes in melt track morphology was also proposed. In a separate study using in-situ and operando synchotron x-ray real time radiography, Leung et al (2018b) reported that for stainless steel 316L, which has a low viscosity melt, spatter generation was observed to have diameters up to 250 µm and an average velocity of 0.26 m/s. Finally, with regards to spattering, Guo et al (2018) reported on the time-scales of the melting, vapour jet/plume formation and argon gas ow formation to be in the micro, tens of micro and lastly hundreds of microseconds respectively.…”