Abstract
In this study, Alloy 247LC samples were built with different laser powder bed fusion (L-PBF) process parameters. The samples were then subjected to solution heat treatment at 1260 °C for 2 h. The grain size of all the samples increased significantly after the heat treatment. The relationship between the process parameters and grain size of the samples was investigated by performing a design of experiment analysis. The results indicated that the laser power was the most significant process parameter that influenced the grain height and aspect ratio. The laser power also significantly influenced the grain width. The as-built and as-built + heat-treated samples with high, medium, and low energy densities were characterized using a field emission gun scanning electron microscope equipped with an electron backscatter diffraction detector. The micrographs revealed that the cells present in the as-built samples disappeared after the heat treatment. Isolated cases of twinning were observed in the grains of the as-built + heat-treated samples. The disappearance of cells, increase in the grain size, and appearance of twins suggested that recrystallization occurred in the alloy after the heat treatment. The occurrence of recrystallization was confirmed by analyzing the grain orientation spread of the alloy, which was lower and more predominantly <1° in the as-built + heat-treated conditions than in the as-built conditions. The microhardness of the as-built + heat-treated samples were high which was plausible because γ’ precipitates were observed in the samples. However, the L-PBF process parameters had a very low correlation with the microhardness of the as-built + heat-treated samples.
Highlights
Alloy 247LC is strengthened by the precipitation of the γ’ precipitate in the γ matrix [1]
The major challenge in printing Alloy 247LC is solidification cracking, which is promoted by their large solidification temperature range and high plastic strains induced by the laser powder bed fusion (L-PBF) process [2]
This paper investigated the influence of the as-built grainsize on the final heat-treated grain size which was not reported in Engeli
Summary
Alloy 247LC is strengthened by the precipitation of the γ’ precipitate in the γ matrix [1]. The super alloy shows adequate fatigue, corrosion, and oxidation resistance at high temperatures. It can be used in the hot section of gas tur bines where the temperature is high (approximately 1200–1370 ◦C) and the environment is highly corrosive [1]. The major challenge in printing Alloy 247LC is solidification cracking, which is promoted by their large solidification temperature range and high plastic strains induced by the L-PBF process [2]. Carter et al [12] investigated the influence of the LPBF process parameters on the crack and void content of CMSX 486. The study revealed that the L-PBF process parameters, for example the laser power and scanning speed, significantly influenced the crack and void contents in the alloy. Thomas et al [13] calculated a normalized volumetric energy density E* for additive manufactured alloys according to Eq (1)
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