Metal Additive Manufacturing Conference - MAMC 2020

Refractory metals belong to the group of transition metals and they are also called “ultra-high temperature materials”. In addition to the high melting temperatures, they have properties that make them suitable for many applications. Tungsten, Molybdenum, and Tantalum produced by laser powder bed fusion process are the subjects of this study. Production of refractory metals by Additive Manufacturing (AM) gives many advantages. The possibility of recycling the unmelted particles is one of the most important aspects for high expensive powders like Ta. Since their high melting point, the energy required to melt a volume of material is given by the focused energy of the laser beam which locally raises the temperature up to the melting point. In addition, thanks to the low percentage of oxygen present in the chamber during the process (≈0,1 %), because of the continuous argon flux, the metal does not oxidize during the process. AM is the only process that allows the production of complex geometry and lightweight refractory metals components, two important features for these kinds of materials, according to their high density and their possible applications in the aerospace field, and for biomedical or future nuclear fusion devices. However, selective laser melting of Ta, Mo, and W faces some challenges due to their main properties: high melting point, heat conductivity and susceptibility to cracks. The purpose of this study is to optimize the process parameters in order to produce high-density refractory metals part by SLM on an EOS M100 (maximum power of 170 W). Characterization is performed through physical properties measurements, microstructural analysis, and evaluation of mechanical and thermal performances. Single Scan Tracks (SSTs) are produced on the top surfaces of the blocks in order to evaluate the process parameters that give regular shape continuous melt-pool . The integrity of the material as a function of the thickness is studied in order to define the production parameters of components with thin wall or complex geometry as lattice structures. Complex benchmarks are produced in order to optimize beam offset for the productions of precise components of refractory metals studied and the angle at which the part is self-sustaining. Surface roughness and surface treatments methodologies suitable for components produced by AM will be studied. The purpose is to verify the influence on the performances during the exercise of the part in a specific application field, such as high energy physics (working temperature range 2000-2200°C) as well as prosthetic systems for biomedical applications (lattice structures for implants).