Characterization and Microstructure of Recycled Eroded Particles from Die-Sink Electro Discharge Machining of H11 Alloy for Applicability in Additive Manufacturing

다국어 초록 (Multilingual Abstract)

Different waste streams from electro discharge machining (EDM) were investigated for an upcycled usage in processes foradditive manufacturing (AM). These erosion sludges accumulate in filter cartridges and at the bottom of machining basins.
The enclosed particles were extracted, sieved and investigated via laser diffraction, dynamic image analysis, scanning electronmicroscopy, optical emission spectroscopy, elemental analysis and flowability measurements. Additionally, thermal,crystallographic and metallographic investigations as well as X-ray micro-computed tomography (μ-CT) were utilized forthe characterization of particle and material properties. In general, eroded powders fulfill the requirements for AM regardingparticle size and shape very well, which is confirmed in morphological investigations and powder flow characteristicsshowing similar properties as the H11 AM reference material. The chemical composition of the powders is equal to themachined H11 alloy, except for the high carbon content. Carbon is entrapped in the iron lattice originating from pyrolysis ofthe present dielectric fluid and the graphite electrode during rapid solidification, which leads to a transition from martensiteto cementite structures. This change is observed in the microstructure of powders, in which acicular primary cementite andaustenite are present. After remelting with slow heating and cooling rates the microstructure changed to ledeburite II withretained austenite and martensitic phases. The pore size and shape distributions obtained by μ-CT measurements showeda pore formation in the compact sample. These results provide a fundament of major properties as well as handling andrecycling suggestions for eroded particles enclosed in waste sludges.