An Investigation of the Materials Science of Metal Vapor Condensate Generated During Selective Laser Melting of Ti6Al4V

Abstract

Advancements in metal additive manufacturing (AM) will enable the development of complex components with lower buy to fly ratio, which is highly attractive for aerospace applications. However, one concern in the process of selective laser melting (SLM) of metals is the particulate waste byproducts. The laser-based process produces ejected material (ejecta) and metal vapor condensate (MVC) that must be vented out of the machine. MVC consists of nano-scale particles that are hazardous and require costly disposal methods that are toxic to the environment. Presently, there is limited understanding of MVC produced from SLM and its reactivity. Here, we explored different techniques to collect and characterize the waste ejecta including MVC produced during SLM with an EOS M 290 printer and Ti6Al4V powder. The ejecta was collected within the printing chamber, on the ventilation exhaust baffle using ex-situ and in-situ methods. Scanning electron microscopy (SEM), dynamic light scattering (DLS) and Energy dispersive X-ray spectroscopy (EDS) was used for characterization of the MVC. Results showed that the in-situ approach to collection was superior, and that the MVC formed agglomerated networks of individual 20-40 nm particles with a chemical composition of higher Al content in comparison to the feedstock powder. A preliminary analysis of the MVC combustion behavior was performed using bomb calorimetry and thermogravimetric analysis (TGA) to quantify the reactivity behavior and to compare the effectiveness of selected passivation methods. Lastly, samples of ejecta were treated with proprietary chemicals to dissolve the metal byproduct, which was found to be an effective method for eliminating the MVC. The significance of the findings and important next steps are discussed.