TY - JOUR
T1 - Modelling freckles and spurious grain formation in directionally solidified superalloy castings
AU - Zhang, Haijie
AU - Zhao, Yunxing
AU - Xiong, Wei
AU - Ma, Dexin
AU - Ludwig, Andreas
AU - Kharicha, Abdellah
AU - Wu, Menghuai
N1 - Publisher Copyright:
© The Author(s) 2024.
PY - 2024/10/19
Y1 - 2024/10/19
N2 - Segregation channels with misoriented spurious grains, known as freckles, are an unacceptable casting defect in superalloy turbine blades. A digital-twin method to predict segregation channels was proposed in our previous studies; however, the formation of spurious grains was ignored. Here, we extend the digital twin methodology by incorporating dendrite fragmentation, which is recognized as the predominant mechanism in the formation of spurious grains. The flow-induced fragmentation process has been refined to account for the timing of dendrite pinch-off. A three-phase mixed columnar-equiaxed solidification model was used to track the motion of the crystal fragments. Directional solidification experiments for superalloy casting were conducted in an industrial-scale Bridgman furnace, and the distribution of spurious grains in the freckles was metallographically analysed. Excellent simulation-experiment-agreement was achieved. Based on this study, the formation of spurious grains within the segregation channels is mainly caused by the flow-driven fragmentation mechanism. Experimentally measured freckles can be reproduced only if the timing of the dendrite pinch-off is considered.
AB - Segregation channels with misoriented spurious grains, known as freckles, are an unacceptable casting defect in superalloy turbine blades. A digital-twin method to predict segregation channels was proposed in our previous studies; however, the formation of spurious grains was ignored. Here, we extend the digital twin methodology by incorporating dendrite fragmentation, which is recognized as the predominant mechanism in the formation of spurious grains. The flow-induced fragmentation process has been refined to account for the timing of dendrite pinch-off. A three-phase mixed columnar-equiaxed solidification model was used to track the motion of the crystal fragments. Directional solidification experiments for superalloy casting were conducted in an industrial-scale Bridgman furnace, and the distribution of spurious grains in the freckles was metallographically analysed. Excellent simulation-experiment-agreement was achieved. Based on this study, the formation of spurious grains within the segregation channels is mainly caused by the flow-driven fragmentation mechanism. Experimentally measured freckles can be reproduced only if the timing of the dendrite pinch-off is considered.
UR - http://www.scopus.com/inward/record.url?scp=85207102716&partnerID=8YFLogxK
U2 - 10.1038/s43246-024-00672-4
DO - 10.1038/s43246-024-00672-4
M3 - Article
SN - 2662-4443
VL - 2024
JO - Communications materials
JF - Communications materials
IS - 5
M1 - 232
ER -