Investigation of segregation and density profiles in the mushy zone of CMSX-4 superalloys solidified during downward and upward directional solidification processes

•Single crystal bars were quenched using downward and upward processes.•The segregation profiles along the mushy zone were examined and compared.•The corresponding density profiles were calculated and compared.•The density increases from dendritic tip to bottom in both quenched mushy zones.•By using...

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Veröffentlicht in:Journal of alloys and compounds 2015-01, Vol.620, p.24-30
Hauptverfasser: Wang, Fu, Ma, Dexin, Zhang, Jun, Bührig-Polaczek, Andreas
Format: Artikel
Sprache:eng
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Zusammenfassung:•Single crystal bars were quenched using downward and upward processes.•The segregation profiles along the mushy zone were examined and compared.•The corresponding density profiles were calculated and compared.•The density increases from dendritic tip to bottom in both quenched mushy zones.•By using downward process (DWDS) the defect of freckles can be essentially avoided. Single-crystal CMSX-4 superalloy bars were casted by using downward (DWDS) and upward (Bridgman) directional solidification processes. The interdendritic segregation along the mushy zone of the quenched samples was measured and the corresponding concentration profiles are comparatively presented. The profiles are translated into liquid density profiles using a numerical model. It was deduced from this observation that, along the mushy zone of DWDS solidified samples, the content of elemental Al increased with increasing distance from the tip of the dendrites, but Re and W gradually decreased. The segregation profiles of these alloying elements in the Bridgman solidified samples demonstrated the same tendency. The results of density calculations suggest that the interdendritic melt becomes lighter with increasing depth in the mushy zone of the Bridgman solidified samples. This indicates that density inversion occurred. The density profiles in the DWDS solidified samples showed an analogous tendency. However, due to the opposite direction of growth, the density inversion did not appear in the DWDSs′ samples. This suggests that the DWDS process can essentially avoid the occurrence of freckles, caused by density inversion, which are serious macro-defects in single-crystal superalloy turbine blade.
ISSN:0925-8388
1873-4669
DOI:10.1016/j.jallcom.2014.09.103