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Investigation of process by-products during the Selective Laser Melting of Ti6AL4V powder
2020-12, Keaveney, Shane, Shmeliov, Aleksey, Nicolosi, Valeria, Dowling, Denis P.
This paper investigates the formation of process by-products during the laser processing of titanium alloy powders by Selective Laser Melting (SLM). The study was carried out during the printing of Ti6AL4V parts using a production scale SLM system (Renishaw RenAM500 M). By-product particles were obtained on the surface of powder removed from the area around where the pulsed laser powder treatments had been carried out. The process by-products examined in this study were damaged Ti6AL4V particles along with condensate. The particles were found to exhibit deshelling, fracture, and collision damage. Based on TEM and SEM examination, the condensate particles were found to have sizes in the nanoscale range and exhibited morphologies, similar to those reported in the literature for welding condensates. Energy-dispersive X-ray spectroscopy (EDX) analysis indicated that the condensate formed from processing Ti6AL4V, exhibited a higher level of aluminum than that obtained for the alloy itself, lower levels of titanium with minimal vanadium levels, were also obtained. This may indicate that the alloy partially decomposes, with the emission of the lower melting point alloying element. The use of an in-situ melt pool monitoring system (called Renishaw InfiniAM Spectral), was evaluated for detecting the presence of these by-product particulates, based on photodiode measurements of the melt pool emissions, along with a camera-based imaging of visual per layer conditions. A reduction in the intensity of infrared emissions was detected, in areas where suspected spatter particles had been redeposited. Thus, demonstrating that process monitoring can be used for the in-situ detection of particulate defects formed during printing.