Effect of Fe Content on the As-Cast Microstructures of Ti–6Al–4V–xFe Alloys

In this work, the evolution of the solidification microstructures of Ti–6Al–4V–xFe (x = 0.1, 0.3, 0.5, 0.7, 0.9) alloys fabricated by levitation melting was studied by combined simulative and experimental methods. The growth of grains as well as the composition distribution mechanisms during the solidification process of the alloy are discussed. The segregation of the Fe element at the grain boundaries promotes the formation of a local composition supercooling zone, thus inhibiting the mobility of the solid–liquid interface and making it easier for the grains to grow into dendrites. With the increase in Fe content, the grain size of the alloy decreased gradually, while the overall decreasing trend was mitigated. The segregation of Fe was more obvious than that of Al and V, and the increase in Fe content had less effect on the segregation of Al and V.

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

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.