Solute redistribution during planar and dendritic growth of directionally solidified Ni-base superalloy CMSX-10

The solute redistribution behavior during directional solidification of the alloy CMSX-10 with planar and dendritic solid/liquid (S/L) interfaces has been investigated by directional solidification and quenching (DSQ) technique. In particular, the elemental partitioning coefficient during the solidification of primary γ and γ/γ′ eutectic was quantitatively estimated by electron probe microanalysis (EPMA) on the sample quenched during planar growth of primary γ and γ/γ′ eutectic, respectively. The EPMA compositional profiles clearly revealed that Scheil solidification occurs during the solidification of primary γ with planar S/L interface. Based on this result, the evolution of γ/γ′ eutectic volume fraction with respect to the solidification rate in dendritic solidification regimes could be rationalized by considering the back-diffusion effect on decreasing the extent of microsegregation. The comparison of the compositional profiles of Cr in the planar grown DSQ sample and the local distribution of Cr in dendritically solidified sample indicated that the solidification of the alloy CMSX-10 completes with the formation of supersaturated γ phase after the γ/γ′ eutectic reaction.