Feasibility Study of the Electron Beam Powder Bed Fusion of Molybdenum

Molybdenum is a promising refractory metal for many high temperature and high stress applications due to the exceptional thermal resistance, high strength and high creep resistance of Molybdenum. The conventional manufacturing methods for molybdenum are problematic due to the high melting point and brittle nature of the molybdenum metal. Additive manufacturing is a promising technology for producing molybdenum parts due to the fact that the additive manufacturing technologies do not require material removal which can create chipping for molybdenum, and the fact that additive manufacturing technologies can create extreme heat in a very small area which is enough for fusing molybdenum powders together. Powder Bed Fusion - Electron Beam (PBF-EB) method was chosen for feasibility manufacturing molybdenum parts in this study. In this study the main focus was on the feasibility of PBF-EB method and the effects of using different rotation angle of the Electron Beam (EB) between the printing of each layer of the 3D parts. This study systematically investigates the feasibility of PBF-EB and the effects of different rotation angles of 67◦ and 90◦ by conducting powder analysis, top surface investigation, Archimedes density analysis, internal porosity analysis, microstructural analysis, thermomechanical analysis, Vickers hardness test and finally the bending test on the printed molybdenum samples and comparing the results. The results of the aforementioned analyses show that the PBF-EB technology has the potential to produce Mo parts with up to 99.37% relative density with 12.27% higher Vickers hardness with columnar grain structure. The results also show that the effects of different rotation angles between 67◦ and 90◦ rotation was minimal in many analyses. Main difference between the two rotation angles were the morphology of the top surface of the printed samples in which 90◦ rotation angle produced much better top surface finish while the 67◦ rotation angle samples had surface cavities filled with unmelted powders on the top surface.