Metal additive manufacturing using powder sheets (MAPS) melts powder attached in a sheet with a polymer binder, avoiding risks of loose powders in material waste, safety and health during laser additive manufacturing among other for e-mobility applications. However, this concept remains challenging for aluminum alloys due to occurring defects. To address this challenge, the mass transfer and defect formation mechanism during MAPS-AlSi10Mg were investigated using high-speed imaging and metallographic observations. The results showed that the mass transfer is realized via droplets formed first from the powder sheet in front of the melt pool and their incorporations into the melt pool. However, a much laser defocusing significantly inhibits the droplets’ incorporation into the melt pool and promotes the balling. Polymer coatings or it wrapped into the AlSi10Mg droplets, generates the inclusions once the droplets were incorporated into the melt pool. Furthermore, under the laser beam in focus, the large particle-size powder sheet, powder side up or low scanning speed easily induce pores via shielding gas/polymer vapor inclusion. The laser defocusing of +15 mm, average laser intensity of  W/cm2, and binder side up induce defect-free tracks, owing to the complete removal of polymers by their sufficient evaporation and powder agglomeration spatters. This work unveils that the droplets’ incorporation into melt pool leads to the mass transfer of MAPS-AlSi10Mg while the droplets containing polymers and gas/vapor inclusion generate inclusions and pores. Meanwhile, the defect-free production strategy of suitable defocusing and high laser intensity is proposed.

This study presents the results of an investigation on the influence of powder feed rate on the microstructure and composition of laser-deposited cobalt–based alloy (MetcoClad21). Optical emission spectroscopy (OES), metallographic analysis, and energy-dispersive X-ray spectroscopy (EDX) was used to characterize the samples and the process. The OES analysis was used to identify element specific atomic emission lines (peaks) within the captured optical process emissions. The elemental composition of the deposited material was observed and peak intensity ratio of certain elements were calculated in situ. The metallographic and EDX analyses were used to measure the cross–sectional–dimensions of the deposition tracks and to analyse the elemental composition of the deposited material. The results showed that the powder feed rate had a significant influence on the microstructure, the cross–sectional–dimensions and the composition within the deposition tracks. Specifically, the authors found that the Fe/Cr peak intensity ratio decreased with increasing powder feed rate, indicating a decrease in the Fe content and an increase in the Cr content of the deposited material. Hence, the peak intensity ratios could have been correlated with the track compositions and the dilution with the Fe-based substrate material. The results of this study have implications for the optimization of laser deposition processes for cobalt–based alloys by an in situ control by OES.

High-power laser interaction with a metal material can induce melting and even evaporation. However, the origin and content of vapor emissions based on temperature, material alloy elements, and other external conditions are not fully understood yet. Therefore, in this study, the content of laser-induced vapor was systematically examined during directed energy deposition processes. Single tracks of aluminum bronze were deposited with both continuous and periodically modulated laser powers. The duration and laser power of the modulations were set to achieve the same total line energy input. With the aid of those laser power modulations, controlled emissions were temporarily excited and observed. Optical emissions were captured with a spectrometer and a high-speed camera and related to the melt pool temperature signals and surface dynamics. The intensity of the emissions as well as the impact on the local chemical composition depend on the modulation parameters. Tracks deposited with short, high-power peaks in the modulation pattern showed chemical compositions comparable to those tracks that were continuously welded, whereby the intensity of spectral emissions was significantly increased. It can be concluded that the intensity of the measured spectral emissions correlates with the measured melt pool temperature signal and the dynamic movement of the vapor plume.

Phase separation is a well-known effect in liquid-liquid interactions, which can also occur during laser-related processes such as laser melting and laser alloying. However, the mechanism of phase separation between immiscible liquids on a millimeter scale during rapid laser processes has not been fully investigated, in which the extent of buoyancy’s contribution to it has remained unclear. Therefore, this investigation focused on the effect of buoyancy on liquid phase separation during the laser melting of silicon (Si) and iron ore. A simplified 2D numerical model was established to simulate the motion of a single Si liquid droplet in iron ore melt with and without the impact of gravity, respectively. The rise velocity of the droplet was calculated and analyzed under the effect of gravity. In addition, the phenomena of simultaneous laser remelting of Si and iron ore in layers were recorded with a high-speed camera, and the element and phase distributions of the target nugget were analyzed by Scanning Electron Microscopy/Energy Dispersive Spectroscopy (SEM/EDS). By combining the simulation, high-speed imaging, and SEM/EDS analysis, the effect of buoyancy on phase separation has been qualitatively analyzed. This investigation revealed that buoyancy is not the main driving force of liquid-liquid phase separation during rapid laser processing.

This paper provides quantitative information about the paths taken by blown powder particles during laser cladding. A proportion of the powder is "wasted" by bouncing off the solid areas surrounding the melt pool. This wastage reduces the productivity and profitability of the process. In this paper, specially developed software was used to analyze high-speed imaging videos of the cladding process, to monitor the directions of powder particle flight toward and away from the melt pool area. This information has been correlated to the geometry and position of the melt pool zone for three different cladding techniques: single track cladding (A tracks), standard overlapping track cladding (AAA cladding), and a recently developed technique called ABA cladding. The results show that the melt pool geometry, and particularly the overlap between the melt pool and the incoming powder stream, has a strong influence on powder catchment efficiency. ABA cladding was found to have considerably better powder catchment efficiency than standard AAA cladding and this improvement can be explained by consideration of the geometries and positions of the melt pools and surrounding solid material in each case. As powder costs are an important factor in industrial laser cladding, the adaption of the ABA technique, and/or control of pool/powder stream overlap (e.g., by making the powder stream not coaxial with the laser beam), could improve the profitability of the process.

The reduction of iron ore powder in a laser-induced thermal cycle using several reducing agents was studied. The laser-assisted reduction process resulted in the formation of iron-rich domains, irregularly embedded in a slag matrix, and transitional phases. The appearance of these various chemical phases was categorized and geometrically evaluated with respect to representative dimensions using scanning electron microscopy. The statistical trends of the morphology are presented, in context with trends of the chemical composition across the domains, to gain a better understanding of the mechanisms behind the reduction process. Iron domains were predominately observed in the vicinity of the Si-rich zones, indicating the occurrence of the reduction reaction as a result of the Fe2O3-Si interaction. Furthermore, different appearances of the Fe-rich domains and other phases in the close proximity to iron were analyzed and discussed based on diffusion and coalescence phenomena. The obtained results show that the reduction occurs, but the process is still uncontrolled and only partially understood. Further analysis and experiments are, therefore, needed to investigate the prospects of the proposed method.

This paper investigates the efficiency of powder catchment in blown powder laser cladding (a directed energy deposition technique). A comparison is made between standard "track by overlapping track"cladding ("AAA"cladding) and "ABA"cladding, where the gaps left between an initial set of widely spaced tracks ("A"tracks), are filled in by subsequent "B"tracks. In both these techniques, the melt pool surface is the collection area for the cladding powder, and the shape of this pool can be affected by several parameters including cladding speed, intertrack spacing, and type of cladding technique. The results presented here are derived from of an analysis of high-speed videos taken during processing and cross sections of the resultant clad tracks. The results show that the first track in AAA cladding has a different melt pool shape to subsequent tracks, and that the asymmetry of the subsequent track melt pools results in a reduction in the powder catchment efficiency. In contrast to this, the geometry of the "B"track melt pools between their adjacent "A"tracks results in an enhanced powder catchment efficiency.

Laser materials processing includes rapid heating to possibly high temperatures and rapid cooling of the illuminated materials. The material reactions can show significant deviations from equilibrium processing. During processing of complex materials and material combinations, it is mainly unknown how the materials react and mix. However, it is important to know which chemical elements or compounds are present in the material to define the alloy. In addition, their distribution after rapid cooling needs to be better understood. Therefore, such alloy changes at rapid heating induced by laser illumination were created as pre-placed and pre-mixed powder nuggets. The energy input and the material ratio between the powder components were varied to identify characteristic responses. For the detection of reaction durations and mixing characteristics, the vapor plume content was assumed to contain the necessary information. Spectral measurements of the plume were used to identify indicators about process behaviors. It was seen that the spectral data give indications about the chemical reactions in the melt pool. The reactions of iron ore components with aluminum seem to require laser illumination to finish completely, although the thermite reaction should maintain the chemical reaction, likely due to the required melt mixing that enables the interaction of the reacting partners at all.

Blown powder directed energy deposition of SS316L powder is carried out on various substrate surface conditions of SS304 such as cleaned, sand blasted, milled, oily, cold galvanised and painted to study their influence on the process. High-speed imaging is used for process observation and the deposited tracks are analysed qualitatively and quantitatively using surface images, cross sectional macrographs and x-ray images. Frames from high-speed imaging reveal the removal of additional material from the substrate surface such as paint and oil. The stages involved in their removal: peeling and evaporation are presented. EDS analysis showed that no additional elements other than powder and substrate material are found in the track volume. The quantitative results for all specimens show that the surface conditions had minor influences on track width, track height, wetting angle, dilution and deposited cross sectional area. Defects such as porosity, inclusions and cracking were not observed related to the surface conditions. These findings could significantly reduce processing time by skipping the cleaning step before directed energy deposition such as laser cladding or repair in industrial applications.