Effect of electromagnetic melt treatment near liquidus on the formation of non-dendrite microstructure of superalloy

The effects of electromagnetic field and melt treatment near liquidus on the grain refinement of the Ni-20Cr-18W(mass fraction,%) superalloy have been studied. The average grain size of 60 kg ingot can be refined to 127 μm and the grains are both fine and globular. Based on the effect of electromagnetic field on atomic cluster, interface stability and transformation from dendritic grain to globular grain, the mechanism of grain refinement has been studied from the aspect of nucleation thermodynamics by OM, SEM, EBSD. The results show that electromagnetic melt treatment near liquidus results in significant refinement. The grain refinement can be attributed to the mechanism that atomic clusters and globular structures can become the nucleus when the initial undercooling reaches certain level. Electromagnetic field not only improves homogeneity of the macroscopic temperature field, but also plays a positive role in interface stability and dendritic to globular transformation, which increases the nucleation rate.