Abstract
In this study, GH4099 superalloys were produced by directed energy deposition (DED) and then heat treated. The microstructural distribution characteristics of the top, middle, and bottom regions along the deposition direction of the samples have been investigated by various microscopic techniques. The results showed that in the as-DEDed state, the microhardness was observed to be lower in the top and bottom regions, but higher in the middle region. The corresponding microstructure was the MC-type carbides precipitating in the bottom and top regions, while the middle region was replaced by M23C6-type carbides. The middle region also had higher dislocation density and recrystallization fraction than the other regions based on electron backscatter diffraction analysis. After heat treatment, only M23C6-type carbides were observed along the grain boundaries, and fine γ' precipitates approximately 30 nm in diameter were dispersed within the γ matrix. In addition, the recrystallized grains were observed at stress concentration locations attributed to high misorientation. The data acquired revealed that modeling the microstructure evolution in the top, middle, and bottom regions can serve as a theoretical guide for achieving a uniform distribution of mechanical properties.
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