OBRABOTKAMETALLOV MATERIAL SCIENCE Vol. 25 No. 1 2023 Results and discussion Metallographic studies of the structure of specimens Changing the heat input naturally affected the structure of the as-manufactured specimens. As the heat input increases, the grains grow and its shape changes. With minimal heat input (0.19 kJ/mm), a bimodal structure with small elongated and equiaxed grains is observed (Fig. 2, a). The medium and high heat input levels 0.25 kJ/mm and 0.31 kJ/mm resulted in forming zigzag-shaped (Fig. 2, b) and large columnar grains (Fig. 2, c), respectively. Annealing of the columnar grained specimens resulted in forming large nonequiaxed grains with numerous annealing twins (Fig. 2. d). Annealing of the pre-deformed by compression specimens led to the most serious structural changes with formation of small equiaxed grains with a large number of annealing twins (Fig. 2, e). The change in the structural state of the specimens is due to differences in the temperature gradient during printing. With low heat input, the crystallization rate increases and as a result, a finer-grained microstructure is formed. In turn, annealing, as well as deformation and subsequent annealing, lead to recrystallization of the material [24, 25]. As a result of printing of the C65500 alloy with the addition of 10 wt.% Al, a fine-grained structure with almost equiaxed grains 25–125 μm in size was formed (Fig. 3, a). Annealing twins and secondary phase inclusions are also observed. When printing with the addition of alloys Al-5Si and Al-12Si, the structure of the specimens looks different. In both cases, dendritic structure is formed (Figs. 3, b and c). Dendrites’ first order axes are oriented along the direction of wall building, and in the interdendritic space there are interlayers of the secondary phase with a thickness of 3–15 μm. a b c d e Fig. 2. Typical microstructure of specimens printed from C65500. Printing modes 1 (a), 2 (b) and 3 (c). Specimens after annealing (d), as well as after deformation and subsequent annealing (e)
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