| Abstract [eng] |
Santrauka anglų kalba / Summary A STUDY OF THE MICROSTRUCTURE OF THE SLS PRINTED PARTS Simonas Mindaugas Jankus The goal of this work was to investigate microstructure of the selective laser sintering (SLS) produced parts. The chemical composition of 316L, GP1, MP1 metal particles and their size distribution were examined usig SEM-EDS technology. EOS EOSINT M280 selective laser sintering 3D printer was used for sample production. 316L, GP1, MP1 metal microparticles were sintered by continuous-wave Yb fiber laser (wavelength 1030 nm), scan speed 7 m/s and 40 μm layer thickness. The sample production required inert nitrogen gas to prevent metal particles from oxidation during 3D manufacturing. The microstructure of cross-section and surface of the produced parts was investigated by using scanning electron microscope (SEM). The surface of the 3D printed samples is measured by an optical prophyllometer. Metallographic analysis of produced parts were applied in pursuance to find out metal crystal structure. Studies have shown that printed samples of 316L and GP1 metal powders had a higher defect content compared printed components from MP1 powder material. From scanning electron microscopy (SEM), it was found that iron-based printed parts melted worse than MP1 components. Varying from 5 to 70 μm microcracks and pairs were observed in sample suface and in cross-section. The poor quality of steel parts was affected by inappropriate production mode. Iron-based 316L and GP1 metal powders did not get enough energy from laser to perform a better microwelding between particles. Steel melting point is higher than Co-Cr alloy. By the way, 316L and GP1 particles have lower thermal conductivity than MP1 material. It is quantitatively characterized by roughness measurements of the surface of the samples. Surface roughness Ra numerical values for samples 316L, GP1, MP1 respectively are Ra= 13,715 μm; 11,412 μm; 3,006 μm. Cross-section of 316L, GP1 and MP1 parts were polished in order to determine crystal structure of the metals. Corrosive hydrochloric acid was used for sample surface etching. The fine-grain martensitic structure has been found in the stainless steel 316L and in the tool steel GP1. Samples from MP1 powder material featured a monolithic structure, i. e. no grain type structure on MP1 parts cross-section has been observed. |
