13th International Conference on Fracture June 16–21, 2013, Beijing, China -1- Mechanical properties of lattice truss structures made of a selective laser melted superalloy Håkan Brodin1,2 * and Jonas Saarimäki2 1 Siemens Industrial Turbomachinery AB, 612 31 Finspång, Sweden 2 Linköping University, Department of Management and Engineering, Division of Engineering Materials, 581 83 Linköping, Sweden * Corresponding author: hakan.brodin@liu.se Abstract Selective laser melting is a free-form manufacturing process, where components are built up layer by layer using metal powder. Complicated geometries can be manufactured and the exact dimensional tolerances allow direct manufacturing with a minimum of post-processing. Many materials are available in powder form today, e.g. aluminium, titanium, stainless steels, tool steels and superalloys. The current work is performed on a nickel based superalloy, conforming in principle to Hastelloy X. Different lattice truss structures were manufactured with the selective laser melting process. In parallel, solid bars were produced with the same manufacturing process. Hollow rectangular tubes and composites of tubes with an interior of lattice truss structures were also manufactured. Hot rolled material of Hastelloy X was included for reference. Mechanical testing was performed in tension. Mechanical testing shows that the selective laser produced material is highly anisotropic and that the material has many advantages compared to the traditionally manufactured Hastelloy X alloy. Tests also show that fracture is promoted along certain planes in the lattice truss structure Keywords free form fabrication, selective laser melting, superalloys, tensile testing, lattice 1. Introduction Free form fabrication, rapid prototyping and 3D-printing are different designations for processes where material can be built to finished or near-finished shape without machining a block of material or casting material in a mould [1-3]. The processes were initially developed for very simple materials, such as thermoset plastics and plaster. Early-on laser was used to melt materials with a low melting point [4, 5], for instance brass. With some free-form manufacturing processes the material with a low melting point was mixed with a material of a high melting point (for instance brass and steel powders). A laser would be able to melt the brass, but steel would not melt, or only partially melt. This method for manufacturing materials would not be sufficient in cases where high stress or elevated temperature use will come into play. With improved process control and higher laser power, the range of materials was expanded. With a higher heat input, more difficult materials are possible to melt and it will be possible to create a microstructure with low amount of porosity and a material without internal defects such as solidification cracks or poor bonding [6]. Free-form fabrication of superalloys is gaining increased interest from the industry, since the available alloys range is growing. Today alloys for selective laser melting include aluminium, titanium, tool steel, stainless steel and heat resistant materials of cobalt- and nickel base [7-13]. In the case of melting of metal powders, the dominating manufacturing process is laser melting, often denoted selective laser melting (SLM) [6], direct laser metal sintering (DMLS) or LaserCusing. All of these names are trade marks for different companies manufacturing equipment for laser melting. The laser melting manufacturing process can briefly be described as a layer-by layer process, where powder is distributed on a powder bed, Figure 1. After powder distribution, the powder is melted
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