MM SCIENCE JOURNAL I 2017 I FEBRUARY 1738 PROCESSING OF NEARLY PURE IRON USING 400W SELECTIVE LASER MELTING – INITIAL STUDY DAVID PALOUSEK, LIBOR PANTELEJEV, TOMAS ZIKMUND, DANIEL KOUTNY Brno University of Technology, Faculty of Mechanical Engineering, NETME Centre, Brno, Czech Republic DOI: 10.17973/MMSJ.2017_02_2016184 e-mail: palousek@fme.vutbr.cz The proposed article deals with development and initial tests of nearly pure iron powder ATOMET Fe AM (Rio Tinto, QMP) using 400W selective laser melting technology. Magnetic properties in conjunction with 3D printing possibilities of metals could be used in many applications. Metal powder was analyzed for verification of distribution and shape of particles. The main laser parameters such as laser power, laser scanning speed and hatch distance were tested to achieve low porosity and sufficient, high building speed. Laser scanning speed was tested in the range from 200 mm/s up to 1400 mm/s and laser power from 100 W to 400 W. The hatch distance was set to the values of 90, 120 and 150 µm. Porosity was evaluated via microscopy image analysis and micro CT. To obtain mechanical properties the tensile testing was performed. KEYWORDS selective laser melting, pure iron, porosity, mechanical properties, pure Fe 1 INTRODUCTION Selective laser melting is an additive powder bed technology of metals which produces parts from fine metal powder using a high-performance laser beam. Metal parts are built layer by layer directly on the base platform. This technology is suitable for production of geometrically complex parts [Contuzzi 2013], [Yan Chunze]. Also, the microstructure is different if compared with standard materials, and material exhibits higher mechanical properties [Casalino 2015]. Processing of pure metal powders using selective laser melting is quite rare except for the area of engineering applications where the interesting metals are e.g. gold or pure titanium. Khan et al. [Khan, 2010] focussed their investigation on the Selective Laser Melting (SLM) of 24 carat gold (Au) powder with a mean particle size of 24 µm. The 50W continuous wave ytterbium-doped infrared fibre laser in the infrared range from 1070 nm to 1090 nm wavelength was used. The best reached porosity was around 10 % for 50 µm of layer thickness. Further research [Khan, 2014] also showed the high porosity to be predominantly between the layers. Sing et al. [Sing 2016] investigated the effect of designs and process parameters on the dimensional accuracy and compressive mechanical behaviour of titanium cellular lattice structures fabricated by SLM. Fabrication of the samples was implemented on a SLM 250HL machine (SLM Solutions Group AG, Germany) equipped with a Gaussian beam fibre laser, power up to 400 W with a focus diameter of 80 μm. Song et al. [Song 2013] showed fully dense iron parts fabricated at the laser power of 100 W using different laser scanning speed. The laser source was YLR-100-SM single mode CW Ytterbium fiber laser (1064–1100 nm). A hydrogen-reduced sponge iron powder, which displays a general multi-prismatic shape, was used. Kruth et al. [Kruth 2004] dealt with selective laser melting of mixture consisting of 50 wt. % Fe, 20 wt.% Ni, 15 wt.% Cu and 15 wt.% Fe3P. He used a Rofin-Sinar Nd:YAG laser source with a wavelength of 1.064 µm and a maximum output power of 300 W in continuous mode. A maximum bending strength of 630 MPa was achieved at a material density of 91%. The main aim of this article is to find mechanical properties for pure iron produced by SLM technigue. 2 MATERIALS AND METHODS 2.1 Standard pure Fe characteristics The general mechanical properties of conventionally processed pure Fe (wrought iron) can be found e.g. in on-line databases and datasheets from producers Goodfellow, Cambridge Ltd., see Tab. 1. Pure Fe Tensile Strength at Break 180-210 MPa Tensile Yield Strength 120-150 MPa Young Modulus 120-150 GPa Boiling point 2750 °C Density 7,87 g/cm 3 Melting point 1535 °C Table 1. Mechanical properties (Goodfellow Cambridge Ltd.) The mechanical properties depend on production process. For example, in the table 2 below, it is possible to find mechanical properties for low-carbon steel. For the exact same alloy AISI 1006 (RioTinto, 0.25-0.40% Mn) the different mechanical properties depending on the process are presented. Table 2. Mechanical properties of different production processes (RioTinto) 2.2 Powder characterisation Powder was used in the virgin state directly from the producer and was not additionally sieved or otherwise processed before its processing. The characterization of water atomized Fe powder (Rio Tinto, Canada) was performed using several procedures. Producer Horiba Median 26.3 µm Mean Size 27.3 µm Std. Dev. 8.8 µm Diameter of Cumulative (%) D10% - 15µm D50% - 28µm D90% - 44 µm D99% - 60 µm D10% - 16.9µm D90% - 38.9 µm Table 3. Particle size distribution Type Carbon (%) Dens. (g/cm³) YS (MPa) UTS (MPa) Elong. (%) Wrought Cold- drawn AISI 1006 Carbon <0.08% 7.87 285 330 20% Wrought Hor- rolled AISI 1006 Carbon <0.08% 7.87 165 295 30%