Quantitative analysis and formation mechanisms of non-metallic inclusions in GH4068 alloy prepared by vacuum induction melting

Abstract

An automatic scanning electron microscope (SEM) analysis system and a self-designed superalloy inclusion analysis module were utilized to characterize the inclusions in the GH4068 Ni–Co-based superalloy prepared by vacuum induction melting (VIM). The morphologies, compositions, and distribution of the inclusions as well as the relationship between the contents of oxygen/nitrogen and inclusion were analyzed. The results indicate that the inclusions in the GH4068 alloy mainly include oxides, carbides, nitrides, carbonitrides and complex inclusions. The oxides are mainly concentrated in the top center of the cast ingots, and their content is higher than that at the bottom and edge. Nitrides and complex inclusions are mainly distributed near the bottom and edge of ingots. The analyses of thermodynamics indicate that the homogeneous nucleation of Al2O3 is spontaneous during the solidification although TiN prefers to wrap on the nucleated particles rather than homogeneously precipitate from the melt. The increase of oxygen/nitrogen content results in the increase of oxides, nitrides and complex inclusions. However, when the concentration of nitrogen is in the range of 3–12 ppm, the increase of nitrogen content shows negligible influence on the content of nitride inclusions.