OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 4 2023 Metallography and elemental analysis The preparation of specimens for metallographic studies and elemental analysis was carried out by cutting it from various sections of the printed plate and then grinding the surfaces using sandpaper with a consistently decreasing grain size of the abrasive. Final polishing was carried out using diamond paste. The microstructure of the specimens was investigated using an Axio Observer A1m Inverted Microscope (Carl Zeiss, Germany) after chemical etching with Kroll’s reagent consisting of 10 mL HNO3, 3 mL HF, and 87 mL H2O. An Oxford Instruments INCA X-Act Energy dispersive X-ray (EDX) spectroscopy on the scanning electron microscope Zeiss EVO 50 XVP (Germany) was carried out to investigate the fine structure and chemical composition of the structural elements. The EDX analysis was performed in two planes with a scanning step of 0.25 µm. Results and discussion Structure and elemental composition Materials fabricated by selective laser melting (SLM) or wire-feed EBAM are characterized by the heterogeneous and anisotropic structure and properties [28], determined by layer-by-layer fusing by the electron beam. It is well known that cooling rates in the majority of conventional casting techniques can range from several tens to a thousand of kelvin per second, which induces significant changes in the structure and properties of the manufactured material. In additive manufacturing, cooling rates of the melt can range from 103 to 108 K/s. Moreover, temperature gradients reach 106 K/cm [37] in some regions. The structural features and its effects on the properties of titanium alloys were most often evaluated using metallography methods and mechanical tests for hardness and strength, mainly under tension, for specimens obtained by selective laser melting [38, 39]. In wire-feed EBAM, when the layer thickness is considerably higher than in SLM, temperature conditions conform with lower cooling rates, that is proven by the columnar structure, presented in fig. 7, а, and the cross-section of columnar crystals in the form of polygons with diagonals of a b c d Fig. 7. SEM images with EDX analysis in XZ (a) and XY (b) planes; microhardness distribution (c); elemental analysis (d)
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