Application of levitation melting to the separation of oxide inclusions from nitrides and carbides in Ni-based superalloy

Abstract

Oxides are usually surrounded by nitrides and carbides in superalloys, which contain high Ti and Nb contents. This makes it difficult to precisely characterize oxide size and composition. Separation of oxides from nitrides and carbides in FGH96 superalloy was carried out by levitation melting to accurately characterize oxides. Manual and automated scanning electron microscopy and energy-dispersive X-ray spectroscopy observations as well as X-ray diffraction were used to characterize inclusions. In the billet, nearly all oxides were surrounded by nitrides and carbides. After levitation melting, however, the majority of oxides were separated, agglomerated and floated to the top surface. The separation efficiency of oxides from nitrides is approximately 85.5%. Oxides were determined as MgO-Al2O3 spinel with the size of 1∼10 µm. Finally, in situ confocal laser scanning microscopy clarified the separation mechanism.