Solidification process and behavior of alloying elements in Ni-based superalloy INCONEL 718

Abstract

The thermal and metallographic analysis revealed that the solidification of Inconel 718 alloy proceeds in order of primary γ at 1615 K, γ/NbC eutectic at 1561 K, and γ/Ni2Nb eutectic at 1452 K. On the other hand, equilibrium evaluation using Thermo-Calc expresses the following solidification sequences; primary γ at 1633 K, followed by γ/NbC eutectic at 1555 K. The γ/Ni2Nb eutectic phase doesn't appear in the equilibrium calculation, indicating that the γ/Ni2Nb phase crystallizes as non equilibrium eutectic phase. The partition coefficients of alloying elements to primary γ and eutectic phases were also determined experimentally (k(Exp.)) and compared with the values estimated with Thermo-Calc (k(T-C)). The behaviors of alloying elements during solidification were estimated by using k(Exp.) and k(T-C) on the Clyne-Kurz model. It was found that both of them are in a good agreement.