Mid Sweden University

Recent developments in metal Additive Manufacturing (AM) technologies have introduced great capabilities unparalleled by conventional manufacturing, not only in achieving freeform geometries, but also in opening new possibilities to tailor the microstructure/properties of materials by controlling process parameters. Electron Beam Melting (EBM) is one of the most important members of the Powder Bed Fusion(PBF) family; it uses a focused electron beam to melt metal powder in a layer by layer approach. One of the main challenges that EBM faces nowadays is the lack of commercially available materials (most of them are Ti-based or Ni-based alloys). Therefore, there is a strong interest to further develop the process for new materials, including steel-based ones. In this investigation two steel-based powders; stainless steel 316L and a tool steel developed by Uddeholm, were used to manufacture functionally graded materials. A special hardware setup using a single powder dispenser was installed in the EBM system, where powders were placed separately to manufacture 10x10x10 mm cubes. SEM images of the specimens’ polished cross sections show a gradual microstructural transition from characteristic 316L one on the bottom of the specimens to the tool steel towards the top. Nanoindentation experiments confirmed a consequent gradient in hardness and elastic modulus, which gradually increase towards top surface. These results show great possibilities to tailor microstructure and mechanical properties by combining different powders in the EBM technology. Potential applications include the tooling industry, where hard and wear-resistant materials are demanded on the surface whether tougher and more ductile behavior is desirable on the core of the tool.