Chonghe Li

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.

This study systematically investigates the synergistic effects of Sr and La-Ce mixed rare earth (RE) additions on the microstructure and mechanical properties of AlSi9Cu3 alloy. The results show that adding 0.02 wt.% Sr and 0.10 wt.% RE together produces the most pronounced refinement, reducing the secondary dendrite arm spacing (SDAS) from 40.12 μm to 26.98 μm and decreasing the aspect ratio of eutectic Si from 12.3 to 7.8. Sr modifies eutectic Si by inducing twin formation and suppressing anisotropic growth, while RE promotes the dispersion distribution of Al₄Ce phases and enhances constitutional undercooling. The synergistic effect leads to a more uniform appearance of dendrites and secondary phases. Consequently, the tensile strength reaches 258.6 MPa, accompanied by a transition in fracture mode from brittle cleavage to ductile dimple fracture. This work provides experimental support for microstructural control and the strengthening–toughening design of AlSi9Cu3 alloys.

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In this study, the metallic Y, CaF₂, and sponge Ti were employed to regulate the composition and achieve the deoxidation of the SHS-TiAl alloy, respectively. The results indicate that the metallic Y could effectively reduce the oxygen concentration of the SHS-TiAl alloys, which could all be controlled below 0.06 wt.%. The alloying control of SHS-TiAl could be further realized by adding sponge Ti with the achievement of a typical α + γ phase microstructure. Additionally, the CaF₂ could adsorb the Y₂O₃ products, which were formed during the deoxidation reaction. However, due to the relatively high initial oxygen content in the SHS-TiAl alloy, the generated Y₂O₃ could not be fully removed, leading to the partial inclusions remaining in the alloy matrix. Also, the residual Y would react with Al in the alloy to form YAl₂ inclusions.

The two-step route combining vacuum induction melting (for alloy homogenization) with electroslag remelting (for inclusion removal) was a well-established technique for the alloy productions. However, because of the extremely high chemical activity of high-entropy alloys containing Ti and Zr, its contamination was uncontrollable during induction melting, which rendered this two-step process impractical for their preparation. Here, we successfully proposed the use of a SrZrO3 crucible with metallic Y to control the oxygen contamination in the alloy, followed by electroslag remelting to eliminate the introduced inclusions during induction melting. The results indicated the oxygen contamination in the alloy was controlled to 0.0445 wt.% during induction melting. A 90 μm dense Y2O3 protection layer was generated on the inner wall of the crucible, which could suppress the further alloy-crucible interaction. Although the generated Y2O3 products could enter into the alloy, leading to the inclusion contamination. Subsequently, the majority of Y2O3 inclusions could be effectively removed by electroslag remelting, and the oxygen concentration was further decreased to 0.018 wt.%. The finally prepared alloy had a compressive strength of 1403 MPa and a compressive strain of 43%, which were comparable to that of the alloy prepared using the vacuum arc melting.

Light alloys, primarily with a aluminum, magnesium, or titanium base, are fundamental to modern engineering due to their advantages of low density and high strength-to-weight ratio