Investigation of Metallic Ca on Enhancing the Cleanliness of Ni-Based Superalloy

Abstract

Induction melting with a crucible was a commonly employed method for the preparation of Ni-based superalloys. However, it inevitably introduced contamination to the superalloy during the melting process. In this study, the effect of Ca addition was investigated on the interaction between the Al2O3 crucible and the superalloy melts. The variations in impurity elements and inclusion contamination for the alloys were studied. The results revealed that the interaction between the melt and the Al2O3 crucible led to the dissolution of Al2O3, introducing oxygen contamination and promoting the formation of inclusions. After adding Ca, the dissolved oxygen readily reacted with Ca to form CaO, which further reacted with the Al2O3 matrix and inclusions to form CaO-Al2O3 oxides. The total O content in the alloy was reduced from 0.0141 ± 0.0005 wt.% to 0.0030 ± 0.0003 wt.%, and the S content decreased from 1.60 ± 0.17 × 10−4 wt.% to 0.82 ± 0.05 × 10−4 wt.%. Meanwhile, the detected area-to-mass ratio of floated inclusion contamination in the alloys decreased from 0.36 cm2/kg to 0.05 cm2/kg. This process reduced both oxygen-related impurities and inclusion-derived contaminants, thereby providing an effective approach for preparing high-purity alloys.