EFFECT OF ELECTROMAGNETIC FIELD ON MICROSTRUCTURE AND MECHANICAL PROPERTY FOR INCONEL 625 SUPERALLOY

Inconel 625 is a Ni-Cr-Mo-Nb alloy which was developed primarily for high turbine applications. The elemental addition of Nb increases the solidification temperature range, which exhibits a strong propensity to form interdendritic segregation. The enrichment of elements Nb and Mo at the terminal stage of solidification leads to the formation of brittle eutectic structure, i.e., gamma+Laves phases, which becomes potential crack origin during the subsequent hot processing and application. The present work has demonstrated that, the introduction of electromagnetic field (EMF) to the solidification process of Inconel 625 alloy has the obvious effect on grain refinement. The EMF can also effectively influence the segregation ratio of Nb and Mo. However, the inappropriate application of electric current intensity and frequency will lead to more severe segregation of elements Nb and Mo, which causes the increment of eutectic structure volume fraction. Further analysis illustrates that both of the grain refinement and eutectic volume fraction control the tensile property at room temperature, increasing the yield strength and decreasing the tensile plasticity for Inconel 625 alloy. It has been proven that a proper selection of input current intensity (100 A) and frequency (8 Hz) can effectively dominate the segregation behavior during solidification process under EMF with more than 30% increase of yield strength and a minute loss of plasticity.