Abstract
Powder bed fusion (PBF) of ceramics is often limited because of the low absorptance of ceramic powders and lack of process understanding. These challenges have been addressed through a co-development of customized ceramic powders and laser process capabilities. The starting powder is made of a mix of pure alumina powder and alumina granules, to which a metal oxide dopant is added to increase absorptance. The performance of different granules and process parameters depends on a large number of influencing factors. In this study, two methods for characterizing and analyzing the PBF process are presented and used to assess which dopant is the most suitable for the process. The first method allows one to analyze the absorptance of the laser during the melting of a single track using an integrating sphere. The second one relies on in-situ video imaging using a high-speed camera and an external laser illumination. The absorption behavior of the laser power during the melting of both single tracks and full layers is proven to be a non-linear and extremely dynamic process. While for a single track, the manganese oxide doped powder delivers higher and more stable absorptance. When a full layer is analyzed, iron oxide-doped powder is leading to higher absorptance and a larger melt pool. Both dopants allow the generation of a stable melt-pool, which would be impossible with granules made of pure alumina. In addition, the present study sheds light on several phenomena related to powder and melt-pool dynamics, such as the change of melt-pool shape and dimension over time and powder denudation effects.
Highlights
There is a growing interest for additive manufacturing in several industries, because of the possibility to build complex and personalized three-dimensional shapes with relatively shortInt J Adv Manuf Technol (2021) 117:2105–2116Juste et al, Verga et al; Moniz et al [4, 6, 9], while the use of other oxide ceramics as absorptance-enhancer within granules was first presented in Florio et al; Pfeiffer et al.; Makowska et al [13,14,15].The choice of additives was never justified by specific material properties, and their effect on laser-matter interaction and on the thermodynamics of the melt pool was never investigated thoroughly
Alumina granules with two different nanometric powder dopants were compared: iron oxide (Fe2O3, L2715D, BASF SE, Ludwigshafen, Germany) and manganese oxide (MnO2, US3319, US Research Nanomaterials, Houston, USA)
Two process characterization techniques have been shown as useful tools for the choice of a suitable dopant for ceramics in L-Powder bed fusion (PBF)
Summary
The choice of additives was never justified by specific material properties, and their effect on laser-matter interaction and on the thermodynamics of the melt pool was never investigated thoroughly. Even though different additives and different processes are presented, process understanding and process characterization are still superficial. Temperature during laser melting of alumina was measured by Qian et al [16]. In-line pyrometry and spectrometry enabled high temporal resolution measurements and proved to be useful for in-situ process monitoring. Their physical meaning is not always easy to interpret, since measurements are spatially integrated, and they refer to the average values of temperature profiles around and within the melt pool
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